DaveInDenver
Rising Sun Ham Guru
I have a couple of fridges at the house so I've been doing some testing with them. Thought it would be an interesting thread to post results.
Portable Fridge Power
- Thread starter DaveInDenver
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DaveInDenver
Rising Sun Ham Guru
Testing inrush on ARB 47L (P/N 10800472) 12V portable fridge/freezer
Current probe is Fluke Y8100
Oscilloscope is Tektronix TDS2014B
Scope setup as follows.
Figure 1 shows the initial power up inrush. The fridge is connected to the 12V source and the inrush occurs when holding the power button down for a few seconds, bringing up the display for the internal temperature. The peak current is 37.4 amps with no appreciable voltage drop on the battery. The inrush lasts 2.5ms and bounced. The compressor started immediately, presumably after the microprocessor stabilized.
Figure 2 shows a relatively long timebase indication of the compressor starting normally as the controller cycles. At 100ms/div the current appears as a step with a peak of 11 amps concurrent with the compressor motor falling into normal operation. Motor looks to take about 60ms to start before falling into regular operation. There’s an initial plateau prior to the motor starting discussed on the next captures.
Figure 3 zooms in to the inrush. You can start to see the peak uncontrolled current. The peak is significant but still obscured in the timebase. There’s a period of 180ms where approximately 3 amps is flowing before the compressor is started. The reason for this is unknown, perhaps capacitor pre-charging.
Figure 4 shows the initial compressor inush. This peaks at 26.2A for approximately 2ms.
Figures 5 and 6 are the compressor during normal run, which averages about 4.5 amps. Vertical scale is 2A/div thus each tick is 400mA. The ripple is therefore about 800mA. Figure 5 trace is using a 4 sample averaging to limit noise while Figure 6 is no averaging, no bandwidth limiting.
Current probe is Fluke Y8100
Oscilloscope is Tektronix TDS2014B
Scope setup as follows.
- Channel 1 is a current probe, range is set to the 20A maximum value. Output is 100mV/A so full 2V signal would represent 20 amps. Scope configured as current probe so display is amps.
- Channel 2 is the voltage at the battery terminals.
Figure 1 shows the initial power up inrush. The fridge is connected to the 12V source and the inrush occurs when holding the power button down for a few seconds, bringing up the display for the internal temperature. The peak current is 37.4 amps with no appreciable voltage drop on the battery. The inrush lasts 2.5ms and bounced. The compressor started immediately, presumably after the microprocessor stabilized.
Figure 2 shows a relatively long timebase indication of the compressor starting normally as the controller cycles. At 100ms/div the current appears as a step with a peak of 11 amps concurrent with the compressor motor falling into normal operation. Motor looks to take about 60ms to start before falling into regular operation. There’s an initial plateau prior to the motor starting discussed on the next captures.
Figure 3 zooms in to the inrush. You can start to see the peak uncontrolled current. The peak is significant but still obscured in the timebase. There’s a period of 180ms where approximately 3 amps is flowing before the compressor is started. The reason for this is unknown, perhaps capacitor pre-charging.
Figure 4 shows the initial compressor inush. This peaks at 26.2A for approximately 2ms.
Figures 5 and 6 are the compressor during normal run, which averages about 4.5 amps. Vertical scale is 2A/div thus each tick is 400mA. The ripple is therefore about 800mA. Figure 5 trace is using a 4 sample averaging to limit noise while Figure 6 is no averaging, no bandwidth limiting.
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DaveInDenver
Rising Sun Ham Guru
Testing inrush on Engel MT45 12V portable fridge/freezer
Current probe is Fluke Y8100
Oscilloscope is Tektronix TDS2014B
Scope setup as follows.
Current measurement location is taken at battery end of cable.
Figure 1 shows voltage and current powering on the fridge. So there's an inrush that's probably a control circuit or inverter capacitors charging. It's 15 minor ticks so 3 divisions at 200mV/division. That 600mV peak represents a 6A initial inrush. It lasts about 3 time divisions at 25 milliseconds per division, so about 75ms before dropping back to nearly zero current drawn.
Figure 2 shows inrush as the compressor starts. That shows a peak of 1.26V and lasts about one division plus a tick or two before settling to the running current. So that's an inrush of 12.6A for, let's say, 35ms.
Figure 3 shows running voltage and current, mean is 273mV indicates 2.73A with a 47Hz ripple. I didn't have min/max measurement on but we can approximate just by sight that the ripple is varying between about 2.5A and 3A to arrive at that mean.
I haven't done anything in depth to understand the ripple. I'm running from a big battery so it's not a power supply artifact. Must be something to do with the fridge. Whether it's the compressor itself, a control circuit or inverter I can't really say. When I measure the sound 47Hz is peak audio frequency (42dB is the SPL at about a foot away, if anyone's interested) so I assume that's the compressor speed.
Looks like there is significant inrush with the Engel fridges. The choice of a 15A fuse doesn't seem off. You could go down one step to a 10A but then you may have to be careful with the time-current game. The time is short enough that a fast acting probably will be fine since the inrushes all seem to be less than 100ms. You'd have to start worrying at about 1 second, at least with an ATC fast type.
Current probe is Fluke Y8100
Oscilloscope is Tektronix TDS2014B
Scope setup as follows.
- Channel 1 is a current probe, range is set to the 20A maximum value. Output is 100mV/A so full 2V signal would represent 20 amps. Scope was configured as voltage probe, so display is in volts.
- Channel 2 is the voltage at the battery terminals.
Current measurement location is taken at battery end of cable.
Figure 1 shows voltage and current powering on the fridge. So there's an inrush that's probably a control circuit or inverter capacitors charging. It's 15 minor ticks so 3 divisions at 200mV/division. That 600mV peak represents a 6A initial inrush. It lasts about 3 time divisions at 25 milliseconds per division, so about 75ms before dropping back to nearly zero current drawn.
Figure 2 shows inrush as the compressor starts. That shows a peak of 1.26V and lasts about one division plus a tick or two before settling to the running current. So that's an inrush of 12.6A for, let's say, 35ms.
Figure 3 shows running voltage and current, mean is 273mV indicates 2.73A with a 47Hz ripple. I didn't have min/max measurement on but we can approximate just by sight that the ripple is varying between about 2.5A and 3A to arrive at that mean.
I haven't done anything in depth to understand the ripple. I'm running from a big battery so it's not a power supply artifact. Must be something to do with the fridge. Whether it's the compressor itself, a control circuit or inverter I can't really say. When I measure the sound 47Hz is peak audio frequency (42dB is the SPL at about a foot away, if anyone's interested) so I assume that's the compressor speed.
Looks like there is significant inrush with the Engel fridges. The choice of a 15A fuse doesn't seem off. You could go down one step to a 10A but then you may have to be careful with the time-current game. The time is short enough that a fast acting probably will be fine since the inrushes all seem to be less than 100ms. You'd have to start worrying at about 1 second, at least with an ATC fast type.
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DaveInDenver
Rising Sun Ham Guru
One take away comparing the ARB to the Engel is inrush profile. A lot of people complain about random shutdown or similar issues with their Danfoss fridges. I've often speculated that inrush would be a concern and this seems to support that assumption.
Why?
Let's say you power your fridge using factory wiring to a back outlet. That's probably rated for 10 A so let's assume Toyota ran a 16 AWG wire for this and it's 20 feet from the fuse block distribution point to the outlet. For the sake of argument assume that the chassis is the return so there's only appreciable resistance in the one hot wire.
A 20 feet length of 16 AWG is 83 mΩ. So if my measurements of inrush is correct, that 26.2 A will yield a 2.17 V drop. Voltage drop is resistance times current, e.g. 0.083 Ω x 26.2 A = 2.17 V.
Let's then say you set you low voltage cut-off to be 11.5 V on the fridge.
So running your alternator is sitting at 13.5 V. But once stopped it's more like 12.5V (or there about). So a 2.17 V drop means the fridge sees 12.5 V - 2.17 V = 10.33 V. That inrush is 2 ms, though, so it's very doubtful the low voltage protection is that fast.
Then the next plateau I saw was about 3 A for 180 ms. That drop is 249 mV. That's not much, 12.5 V - 0.249 V = 12.251 V at the fridge.
The next step was the what looks like the motor actually starting. I saw a 11 A peak for that. On that 16 AWG wire the drop is 911 mV, about 0.91 V, so your 12.5 V battery gets you 11.59 V at the fridge. That lasted for about 60 ms. So whether that's long enough to trip the under voltage protection seems unlikely but not all designers are going to do the same thing. I'd personally window the voltage to stretch out to seconds at least. Ideally you'd want to see some sampling and perhaps a value held across more than one cycle to develop a trend. But that all depends on how much horsepower their microprocessor has. I'd guess it's pretty minimal so holding more than a few samples over time is asking a lot.
Then it settled into running. I saw about 4.5 A for that. On the 16 AWG wire that's 373 mV of drop. On a fresh battery that's no problem, 12.5 V - 0.373 V = 12.13 V. But your low voltage trip is 11.5 V + 0.373 V = 11.87 V is the lowest your battery can reliably go in that case.
Why?
Let's say you power your fridge using factory wiring to a back outlet. That's probably rated for 10 A so let's assume Toyota ran a 16 AWG wire for this and it's 20 feet from the fuse block distribution point to the outlet. For the sake of argument assume that the chassis is the return so there's only appreciable resistance in the one hot wire.
A 20 feet length of 16 AWG is 83 mΩ. So if my measurements of inrush is correct, that 26.2 A will yield a 2.17 V drop. Voltage drop is resistance times current, e.g. 0.083 Ω x 26.2 A = 2.17 V.
Let's then say you set you low voltage cut-off to be 11.5 V on the fridge.
So running your alternator is sitting at 13.5 V. But once stopped it's more like 12.5V (or there about). So a 2.17 V drop means the fridge sees 12.5 V - 2.17 V = 10.33 V. That inrush is 2 ms, though, so it's very doubtful the low voltage protection is that fast.
Then the next plateau I saw was about 3 A for 180 ms. That drop is 249 mV. That's not much, 12.5 V - 0.249 V = 12.251 V at the fridge.
The next step was the what looks like the motor actually starting. I saw a 11 A peak for that. On that 16 AWG wire the drop is 911 mV, about 0.91 V, so your 12.5 V battery gets you 11.59 V at the fridge. That lasted for about 60 ms. So whether that's long enough to trip the under voltage protection seems unlikely but not all designers are going to do the same thing. I'd personally window the voltage to stretch out to seconds at least. Ideally you'd want to see some sampling and perhaps a value held across more than one cycle to develop a trend. But that all depends on how much horsepower their microprocessor has. I'd guess it's pretty minimal so holding more than a few samples over time is asking a lot.
Then it settled into running. I saw about 4.5 A for that. On the 16 AWG wire that's 373 mV of drop. On a fresh battery that's no problem, 12.5 V - 0.373 V = 12.13 V. But your low voltage trip is 11.5 V + 0.373 V = 11.87 V is the lowest your battery can reliably go in that case.
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DaveInDenver
Rising Sun Ham Guru
So to fix it people recommend bumping up and doing a proper run. Now in this case you go to 12 AWG but let's say you do a complete out and back run instead of using the chassis for the return. There's draw backs and benefits but doing the full run is generally more reliable and safer.
Now a 20 feet distance is actually a 40 foot loop, so 65.5 mΩ. Better, but might not solve it completely. If you just do a hot side run and use the chassis it would be closer to 32.75 mΩ. Next, some do a really good run of 8 AWG. That is 12.95 mΩ for the 20 foot run, 25.9 mΩ for a full out-and-back.
Let's say you did 12 AWG and the loop is 40 feet and it's running current that trips the low voltage. At 4.5 A your battery minimum is 11.5 V + (4.5 A x 0.0655 Ω) = 11.79 V. That's a pretty deep discharge that you're unlikely to hit all that often.
As a comparison you can see why you don't hear as many complaints about the Engel for this. The draw is quite a bit lower. Even running on a factory harness it's going to take a fairly deeply discharged battery to hit 11.5 V.
Now a 20 feet distance is actually a 40 foot loop, so 65.5 mΩ. Better, but might not solve it completely. If you just do a hot side run and use the chassis it would be closer to 32.75 mΩ. Next, some do a really good run of 8 AWG. That is 12.95 mΩ for the 20 foot run, 25.9 mΩ for a full out-and-back.
Let's say you did 12 AWG and the loop is 40 feet and it's running current that trips the low voltage. At 4.5 A your battery minimum is 11.5 V + (4.5 A x 0.0655 Ω) = 11.79 V. That's a pretty deep discharge that you're unlikely to hit all that often.
As a comparison you can see why you don't hear as many complaints about the Engel for this. The draw is quite a bit lower. Even running on a factory harness it's going to take a fairly deeply discharged battery to hit 11.5 V.
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Inukshuk
Rising Sun Member
Very nice deep dive.
Often once people go to the prong and screw type ARB plug (or another type that is not cig lighter style with spring loaded tip) the ARB shutoff issue goes away. Can that voltage drop be tested?
Overall, I am shocked by the 37.5 amp ARB 47qt inrush.
Often once people go to the prong and screw type ARB plug (or another type that is not cig lighter style with spring loaded tip) the ARB shutoff issue goes away. Can that voltage drop be tested?
Overall, I am shocked by the 37.5 amp ARB 47qt inrush.
DaveInDenver
Rising Sun Ham Guru
It can. I know Romer and Corbet were just talking about that so it would be an interesting test. I don't know if I've ever seen a spec for what it's supposed to be, though. It would take very sensitive test equipment, a DMM probably would not read it. My current probes would not, although on mA a DMM shunt may get a rough value of it.
For comparison Anderson does give a spec for a standard PowerPole, which for the smallest terminals (15A for 16 to 20 AWG wire) is 875 μΩ. Note the prefix is micro-Ohm so it's 0.875 mΩ. The voltage drop at 15 amps for this would be 13.125 mV (it's small, 0.013125 V)
I wouldn't think a properly functioning cigarette plug is actually going to be all that much worse to be honest. They're rated for 10 amps in most cases and that would imply they'd expect tens of mΩ otherwise they'd be melting all the time.
So if I was to hazard a guess the main problem is one of two.
First is "properly functioning" is a major assumption. Those things are prone to falling out from vibration and the springs losing their flex.
Second is corrosion. Legitimate PowerPoles are silver plated so fairly immune to most things. Cigarette plugs may be chrome, nickel (such as Blue Sea uses) or most anything shiny. Quality is going to vary I imagine.
Don't read too much into that. Inrush is a matter of resistance (and impedance, strictly speaking), current and time.
More important, though, is impedance. Impedance is resistance of a device that operates on alternating current. The total current that flows is a function of both DC and AC.
A motor winding (an inductor) has both resistance and impedance. So do electronic devices like capacitors and transistors. So the inrush on a circuit may have a very low initial DC resistance but once an electric or magnetic field builds up the impedance completely changes the amount of current flowing. Doesn't always mean the current goes down but usually that's the case.
So look at the time for that inrush. It's very short, 2/1000th of second. A fuse reacts in hundreds of milliseconds up to tens or hundreds of seconds, perhaps minutes or hours. For a fuse to trip in 2 millisecond would take probably thousands of amps. This is due to heating and heat is a function of current and time, exponentially.
Just to belabor the point. Think about your laptop power supply. When you plug it in after it's been sitting for a while you may get a small arc on the plug. That's inrush to the big caps in it. That doesn't hurt anything for the most part. That's basically what is happening with that ~37 amps when I turned on the fridge. All the "stuff" inside getting it's first power.
I was a little surprised by the ~26 amps when the compressor was going to turn on. The 11 amp surge when the motor starts I expected.
The Engel did that, too. It was lower but still significant. When you turn it on there's about 6 amps of inrush to the control circuit and each time the compressor starts it's about 12 amps of surge. If I was looking at this from my perspective as a designer I'd just say whomever did the Engel paid more attention to cap charging or perhaps mitigating FET inrush.
I don't want to suggest it's not important, cumulative or immediate damage can occur with any inrush. But it's also not surprising. Anecdotally, you know how some people say their whatever is left running forever while some people who turn them off seem to get less life? This is partially why. Turning on a TV or computer or fridge, or indeed starting your engine, is by far the most damaging time for it.
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DaveInDenver
Rising Sun Ham Guru
Rebuilt the portable battery box I use to power the fridge. The enclosure is just 1/2" plywood. Plywood good, no sparky!
The problem is that I made it fit the old battery perfectly as well as in my truck bed. It wouldn't fit a 100 A-hr standard LiFePO4 by 1/2" and a 50 A-hr was giving up a lot of space. So I custom made a new battery for it.
I have a pair of 25A PowerPole outputs, a dual USB outlet, external solar and DC-DC inputs. There's a spare 25A PowerPole pigtail inside for misc stuff.
It had a group 25 Odyssey that gave up the ghost a couple of months ago. So took the opportunity to dump many pounds and increase capacity. A G25 Odyssey is given as 65 A-hr and I usually got about a day and a half without charging before depth of discharge hit critical. But even when it was still good I was only able to suck out 40ish A-hr before it hit the falling off a cliff point. Routinely doing so probably did the Odyssey no favors, too.
Used some new-old stock LEV60 LiFePO4 cells and an Overkill Solar 120A BMS (current limited to 1C battery capacity). Littelfuse Mega main fuse and 6AWG wire are technically fine for full 120A the BMS can handle, though. The cells are rated 74 A-hr, so ~60 A-hr is the goal for a cycle capacity. Lithium doesn't have a problem doing 100% depth of discharge but still keeping them between 10% and 90% extended their life.
Top balancing the cells, set up temporarily in a parallel bank and using a regulated bench supply. A few days to get to and stabilize at 3.45V and then a couple hours one morning bird dogging to bring them to 3.65V.
The cells are held in a jig I made up. Plates on the side with a gentle squeeze using 10-24 threaded rod. Rubber sheet isolation between and on the sides, some foam to cushion. The battery bus bars are 1" double (tubular) braided and tinned copper that I brazed copper washer onto for mechanical stability. A little kink in the middle to allow expansion and contraction without stressing the lugs.
The box already had the Morningstar Sunsaver MPPT (15A solar charge) and Victron Orion-TR Smart (18A DC-DC charger) that I re-used. The Morningstar is old enough to pre-date widespread use of lithium so it's variables take some creative values to get right.
The problem is that I made it fit the old battery perfectly as well as in my truck bed. It wouldn't fit a 100 A-hr standard LiFePO4 by 1/2" and a 50 A-hr was giving up a lot of space. So I custom made a new battery for it.
I have a pair of 25A PowerPole outputs, a dual USB outlet, external solar and DC-DC inputs. There's a spare 25A PowerPole pigtail inside for misc stuff.
It had a group 25 Odyssey that gave up the ghost a couple of months ago. So took the opportunity to dump many pounds and increase capacity. A G25 Odyssey is given as 65 A-hr and I usually got about a day and a half without charging before depth of discharge hit critical. But even when it was still good I was only able to suck out 40ish A-hr before it hit the falling off a cliff point. Routinely doing so probably did the Odyssey no favors, too.
Used some new-old stock LEV60 LiFePO4 cells and an Overkill Solar 120A BMS (current limited to 1C battery capacity). Littelfuse Mega main fuse and 6AWG wire are technically fine for full 120A the BMS can handle, though. The cells are rated 74 A-hr, so ~60 A-hr is the goal for a cycle capacity. Lithium doesn't have a problem doing 100% depth of discharge but still keeping them between 10% and 90% extended their life.
Top balancing the cells, set up temporarily in a parallel bank and using a regulated bench supply. A few days to get to and stabilize at 3.45V and then a couple hours one morning bird dogging to bring them to 3.65V.
The cells are held in a jig I made up. Plates on the side with a gentle squeeze using 10-24 threaded rod. Rubber sheet isolation between and on the sides, some foam to cushion. The battery bus bars are 1" double (tubular) braided and tinned copper that I brazed copper washer onto for mechanical stability. A little kink in the middle to allow expansion and contraction without stressing the lugs.
The box already had the Morningstar Sunsaver MPPT (15A solar charge) and Victron Orion-TR Smart (18A DC-DC charger) that I re-used. The Morningstar is old enough to pre-date widespread use of lithium so it's variables take some creative values to get right.
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LARGEONE
Rising Sun Member
I should have you challenge my cheap China AlpiCool fridge!
I’ve been running it off of a 100ah LiTime LiFePo4 battery when I’m not driving. Seems to last several days at least which keeps me from running down my main battery.
I’ve been running it off of a 100ah LiTime LiFePo4 battery when I’m not driving. Seems to last several days at least which keeps me from running down my main battery.
DaveInDenver
Rising Sun Ham Guru
First partial cycle was encouraging. Ran two fridges for about 12 hours, recharged a few devices. I usually see about 1.5 A-hr per hour used by these fridges so 2 x 1.5 A-hr/hr x 12 hours should be about 36 A-hr. They're inside so duty cycle is probably low.
Drew down to about 70% and took about an hour to fully recharge with a 30A bench supply into the Victron. Returned 27.25 A-hr back into the battery according to the external power gauge. The BMS thought 23 A-hr was used, so there's some normalizing and balancing still a-doing.
It's also possible since I was tweaking settings that I lost some of the fuel gauge during one of the updates to them. So the next discharge and charge cycle I hope will agree better. I don't have an independent Coulomb meter in the system, so it's the internal BMS or nuthin' for it.
Worst case I saw was 11mV cell-to-cell imbalance. The BMS can balance a little bit but that's going to take a few cycles to happen. The worst difference was during the meat of the bulk, so I'm supposing batch variance. These cells aren't matched or anything, just bulk unused surplus cells.
Drew down to about 70% and took about an hour to fully recharge with a 30A bench supply into the Victron. Returned 27.25 A-hr back into the battery according to the external power gauge. The BMS thought 23 A-hr was used, so there's some normalizing and balancing still a-doing.
It's also possible since I was tweaking settings that I lost some of the fuel gauge during one of the updates to them. So the next discharge and charge cycle I hope will agree better. I don't have an independent Coulomb meter in the system, so it's the internal BMS or nuthin' for it.
Worst case I saw was 11mV cell-to-cell imbalance. The BMS can balance a little bit but that's going to take a few cycles to happen. The worst difference was during the meat of the bulk, so I'm supposing batch variance. These cells aren't matched or anything, just bulk unused surplus cells.
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My switch to Anderson connectors simply cured poorly functioning cig style plugs. The worst being the Hella style which really don’t play well with aftermarket female plugs. Or even many OEM. I recently swapped out the rear OEM receptacle in my wife’s Outback for an Anderson. Her fridge issues have been solved. My Engel’s cig style plug worked great. None of my other fridges had good plugs. They have all be changed out. The Engle is awaiting its new 250-series chariot. I’ll probably swap it then for an Anderson just so everything can move around.
@DaveInDenver
Did you do any testing to determine power needs over time? I’m looking at portable battery options for my 250-series to run my old Engel MT-45. Would like 2 days worth of power then obviously have the truck charge the battery while driving. I could do that with the 110ac inverter or wire it to an ignition hot 12v source. I’ve been looking at these plug and play options. Just need to decide on the size.
Did you do any testing to determine power needs over time? I’m looking at portable battery options for my 250-series to run my old Engel MT-45. Would like 2 days worth of power then obviously have the truck charge the battery while driving. I could do that with the 110ac inverter or wire it to an ignition hot 12v source. I’ve been looking at these plug and play options. Just need to decide on the size.
I have the River Pro with the extra battery. The base unit will run my ARB 63 quart for a couple of days without the extra battery. That is assuming the ambient temp isn't over about 80 degrees and the fridge is pretty full and kept closed mainly. 
The EcoFlow charges much faster than my ancient Jackery 500.
The EcoFlow charges much faster than my ancient Jackery 500.
That’s good to hear. I was hoping to get away with a smaller unit but figured the pro is what I really need. I just recently got one of the larger Delta units to back up our Starlink in the event of power outages. I’m getting ready to completely ditch my land line and need the wifi for our cell phones as we are outside coverage areas.
DaveInDenver
Rising Sun Ham Guru
As it happens I did run a total capacity (to fully dead) test about 3 weeks ago on this new LFP battery box using my circa 2007 MT45. It was controlled conditions in the basement with about a 12 pack of beer in it (lots of air) at 1.5 on the dial. The lid was never opened.
Got at least 59 hours starting from 100%. At 59 hours the BMS read 20%, said I had around 15 A-hr left. I let it go until the point the BMS turned the output off. My battery is rated 74 A-hr.
I unfortunately don't know exactly the run time to complete discharge, though, since my test tool failed me. I just know next time I checked (about 10 hours later) the fridge was off and the BMS at max discharge fault. So it had to be somewhere between 59 hours and 1 minute or roughly 69 hours. My suspicion is probably not much more than a couple more hours since the temperature of the fridge was about 10°F below room temp and had mostly defrosted and puddled. It's normally about 36°F inside and the room (basement) is usually about 65°F.
Using 59 hours works out to 1.25 A-hr/hr or 30 A-hr per day, which is inline with my historical observations (roughly 40 watts running and around 50% duty cycle) and would suggest that my BMS is significantly optimistic and conservative towards protecting the cells. I know this is true on charge. It'll indicate 100% and 74 A-hr available while an external monitor will still read that more energy is returned (around 1% to 2%) before the battery is really 100%. So the BMS in this case is incorrect under 10% and over 90% and not Coulomb counting very accurately (current per time being the reliable way to measure usage with lithium). That jives with showing I still had 20% capacity but it only actually lasting maybe 10% longer before risking cell damage. My assumption in this matter is being capable of 120A that resolution under 1A is too course to really read the current tail. My external test shunt is lab and not field quality, so at least one decimal point more accurate.
So I'm building up a different set of tools to run another test to get exact, repeatable and documented numbers for total consumption, consumption rate and precise charge and run time. TBD.
My goal was being able to ride through two nights and a day without solar or driving. So set up camp on a Friday evening followed by a rainy Saturday then driving again or deploying solar Sunday has been easily doable in all weather. It's what really set this whole LFP conversion in motion. I had a 65 A-hr AGM and it aged so quickly from me skipping daily charges and constantly going deep into discharge.
The main advantage (neglecting size and weight) of lithium over lead-acid is how depth of discharge works. On AGM you should try to stay above 50% DOD and be methodical about getting to 100% on a 3-step profile. Doing this gets you perhaps 500 cycles. While LFP is happiest between 10% and 90% and tolerates fast bulk-only charges. I'm being conservative trying to stay between 20% and 90% and C/4 (or less) discharge rates on mine. Doing this I hope can yield 5,000 cycles.
Got at least 59 hours starting from 100%. At 59 hours the BMS read 20%, said I had around 15 A-hr left. I let it go until the point the BMS turned the output off. My battery is rated 74 A-hr.
I unfortunately don't know exactly the run time to complete discharge, though, since my test tool failed me. I just know next time I checked (about 10 hours later) the fridge was off and the BMS at max discharge fault. So it had to be somewhere between 59 hours and 1 minute or roughly 69 hours. My suspicion is probably not much more than a couple more hours since the temperature of the fridge was about 10°F below room temp and had mostly defrosted and puddled. It's normally about 36°F inside and the room (basement) is usually about 65°F.
Using 59 hours works out to 1.25 A-hr/hr or 30 A-hr per day, which is inline with my historical observations (roughly 40 watts running and around 50% duty cycle) and would suggest that my BMS is significantly optimistic and conservative towards protecting the cells. I know this is true on charge. It'll indicate 100% and 74 A-hr available while an external monitor will still read that more energy is returned (around 1% to 2%) before the battery is really 100%. So the BMS in this case is incorrect under 10% and over 90% and not Coulomb counting very accurately (current per time being the reliable way to measure usage with lithium). That jives with showing I still had 20% capacity but it only actually lasting maybe 10% longer before risking cell damage. My assumption in this matter is being capable of 120A that resolution under 1A is too course to really read the current tail. My external test shunt is lab and not field quality, so at least one decimal point more accurate.
So I'm building up a different set of tools to run another test to get exact, repeatable and documented numbers for total consumption, consumption rate and precise charge and run time. TBD.
My goal was being able to ride through two nights and a day without solar or driving. So set up camp on a Friday evening followed by a rainy Saturday then driving again or deploying solar Sunday has been easily doable in all weather. It's what really set this whole LFP conversion in motion. I had a 65 A-hr AGM and it aged so quickly from me skipping daily charges and constantly going deep into discharge.
The main advantage (neglecting size and weight) of lithium over lead-acid is how depth of discharge works. On AGM you should try to stay above 50% DOD and be methodical about getting to 100% on a 3-step profile. Doing this gets you perhaps 500 cycles. While LFP is happiest between 10% and 90% and tolerates fast bulk-only charges. I'm being conservative trying to stay between 20% and 90% and C/4 (or less) discharge rates on mine. Doing this I hope can yield 5,000 cycles.
tl;dr
Based on this I'd be comfortable that my MT45 and 74 A-hr box will last 36 hours without charging or requiring special handling (e.g. it could be opened and used normally even if it's warm) while preserving the life of the cells. That is giving me perhaps as much as 40% margin but I think certainly ~25% and sizing based only running an Engel would be to take rated capacity (e.g. amp-hours) and divide by 2 to give safe run time. A 100 A-hr lithium would then be a 50 hour battery with margin to run around 1/2 to a full day over your planned charging interval. To convert EcoRiver I'd suggest watt-hour capacity divided by 12.8V, that being 3.2V/cell or 20% state of charge point.
BTW, it took a little more than 3 hours to get from 0% back to 90% using a 30A supply. My DC-DC tops at 220W, so ~18A into the battery and that is the bottleneck.
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I have been tracking power usage on my Engel MT-45 since I installed a 230 ah LiFePO4 in my taco.
I use around 23 ah per day when driving around and camping as measured by my Victron BMV-712 battery monitor.
The Engel is kept full and around 28-30 degrees Fahrenheit and is turned off while I’m sleeping on it and back on as soon as I wake up.
I have a few other minor loads like intermittent phone & tablet charging, but the main load is the fridge.
I consistently use 10% of my 230 ah battery per day. When I’m camped for a few days at the same spot I can reclaim all of the energy used that day by hooking up my 100 w solar panel.
Been running my MT-45 combi off a 30ah lifepo4 for a few years now. It would last roughly 24 hours but would need driving after that. I was charging it on alternator voltage so I don't think it ever fully charged.
Added solar and now its bulletproof. So far haven't come close to losing refrigeration under any condition, constant 2C.
Added solar and now its bulletproof. So far haven't come close to losing refrigeration under any condition, constant 2C.
Screenshots of the power I used on my last six day long trip to Grand Canyon-Parashant National Monument.
Six days usage from 2024-08-29 6:00 AM to 2024-09-03 6:00 PM took me from 100% to 40% of the 230 AH battery. Running the Engel I rarely draw more than 3 amps. The one five amp dip was charging the laptop.
Five days to recharge using my 100 watt solar panel just sitting flat in the back of the truck after I got home. With careful aiming throughout the day I have gotten over 600 watt hours out of the solar panel - way more than enough to run the Engel through the day & night. Laying flat & un-aimed I get around 300 wh per day out of the panel.
Temperature a lot hotter in southern Arizona than up north
Watts for the Engel were averaging 13 & 27 with a few 40s (probably cellphone charging) and one 65 watts when charging the laptop.
230 AH battery usage since January 2024.
Six days usage from 2024-08-29 6:00 AM to 2024-09-03 6:00 PM took me from 100% to 40% of the 230 AH battery. Running the Engel I rarely draw more than 3 amps. The one five amp dip was charging the laptop.
Five days to recharge using my 100 watt solar panel just sitting flat in the back of the truck after I got home. With careful aiming throughout the day I have gotten over 600 watt hours out of the solar panel - way more than enough to run the Engel through the day & night. Laying flat & un-aimed I get around 300 wh per day out of the panel.
Temperature a lot hotter in southern Arizona than up north
Watts for the Engel were averaging 13 & 27 with a few 40s (probably cellphone charging) and one 65 watts when charging the laptop.
230 AH battery usage since January 2024.
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DaveInDenver
Rising Sun Ham Guru
@Stepmurr, are you happy with the Victron monitor? Seems like a good unit. Easy to get calibrated?
One of the first starts this morning of the fridge. Pulled ~45W. The only thing on the battery is the fridge. It was beautifully cool in northern Utah this week! Fridge was inside overnight plugged into the mains so it was already cool inside.
A typical charge after the alternator stabilized, battery starting to warm up.
Then the min/max charge and discharge at the end of the day this afternoon once we got home about 7 hours later.
One of the first starts this morning of the fridge. Pulled ~45W. The only thing on the battery is the fridge. It was beautifully cool in northern Utah this week! Fridge was inside overnight plugged into the mains so it was already cool inside.
A typical charge after the alternator stabilized, battery starting to warm up.
Then the min/max charge and discharge at the end of the day this afternoon once we got home about 7 hours later.
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Yes, I'm an admitted Victron fanboy. The BMV-712 is great and I trust it. The first solar charge of the batteries was invalid as the BMV-712 said they were 100% two days before the battery BMS actually finished charging on solar, but after the first synchronization it has read accurately on subsequent charges. Now it reads 100% just a few hours before the battery BMS stops the solar charge cycle.
The 230 AH battery in my Taco is one half of the system I built for my travel trailer. I put a 275 Amp Anderson Power Pole on the battery so I can move it from trailer to Taco. The moveable battery has the shunt & BMV-712 attached. The trailer is a 24 v system with two 230 AH LiFePO4 batteries, Victron MultiPlus II 24/3000 inverter, Victron 70 amp 24-12 DC to DC converter, and Victron Cerbo GX communications centre.
The Taco has a Victron 30 amp solar charger and Victron 30 amp 12-12 DC-DC charger bolted onto the Engel fridge frame. I have only used the DC-DC charger once when I ran the fridge all day long on a 115 degree day at work prior to heading off for a week long camping trip so I knew the battery was topped off. The other three full charges have all used the solar panels on the trailer or Taco.
I have been so impressed with the new LiFePO4 battery setup that I am considering removing the dual battery setup in the Taco. Having three large batteries in the Taco seems like overkill, and right now the only benefit the dual battery setup has is when winching, and I seldom winch. If my Taco primary battery goes dead I can always re-wire the Victron DC-DC charger to charge it from the LiFePO4 battery.
I also have Victron battey sensors on all my vehivle batteries. This is the screenshot of the Taco batteries the night I returned from my Grand Canyon-Parashant trip. The two engine compartment batteries were attached to my Battery-Minder charger and the 230 AH battery had not seen solar charging yet.
Having all my battery information on one app is extremely handy.
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