Losing my patience with AGM batteries

[RayRay27]

It's important to know the direction of the diode in this trick is critical. You want the forward voltage drop added to the circuit. Backward will trick the alternator into thinking there's no sense voltage and not regulate at all.

I make this point because not every truck's fuse box is identical and if you build a gadget using one of the Tap-A-Fuse blocks using a visual reference from the Interwebz it's possible to have things oriented wrong or not fit. By turning it around like this I was able to leave a nice length loop on the wire for strain relief rather than trying to cut the plastic and re-seal everything.

For example on a 2nd gen Tacoma the Alt-S location required a different arrangement to fit against the side and for the lid to fit back on.

This was also a Schottky I tried in an experiment, which gave less voltage bump (about 0.3V) because in the summer having too high of a voltage is just as damaging as too low. A junk box 1N4001 was pushing up against 15V on my truck and holding that for hours on the Interstate in August can cause venting. That's very bad to do on an AGM since there's no way to put the magic juice back inside unlike traditional flooded types where you can add back water if you boil it. An AGM (or maintenance-free for that matter) will vent if you push them too hard to prevent over pressure and if it does that's a one-way turn down Ruined Street.

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In the end, though, I just ended up using a diode fuse from a Ford truck. The one I got was about 0.5V drop and works for my purposes almost year-round and fits inside the fuse box much cleaner. I just put the hobbled one in during long road trips in the summer now.

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So my question would be where would you plug it in on a 80 series and is the new diode wired in the correct direction. See diagram for 80 series.

 

[bassguyry]

Helpful info! Thanks, Dave! I was hoping you'd chime in here.

Based on the pictures you posted, it looks like my diode is wired reverse from yours. I'd be interested to know if the 80 is wired similar to your 2nd gen Taco.

 

[AimCOTaco]

I'd replace the 7.5A charging fuse with the booster rig. (or whichever fuse is in the line used to sense the battery voltage)
Check voltage response to verify/test the polarity. No (low low) risk.

EDIT: this may not be correct for the 80 schematic above.. we want the booster in the line used to sense the battery voltage.

IG -is the line that turns the charging circuit on.
L -as I understand it, can be thought of like an alarm output of sorts. Some 'yotas feed it to the ECM, others direct to the battery lamp.
S -is the sense line where I have my booster on the 100 series, for the 80 it looks like that line has a 50A large fuse and a fusible link?
B - is the the main charging lead that carries the current.

You guys should definitely second guess me on 80 stuff.

 

[bassguyry]

To be clear, I used @AimCOTaco's instructions from Mud (read: "interwebz") to build the booster, and he is INFALLIBLE. So, there.

 

[nakman]

Awesome tech here... one of these days I want to do this on the GX, as it sits pretty much at 13.1 on the highway all day, would love to bump that up a little more. I just need to get my head into this a little more... should be the same mod as a 100 though, right? I mean, same engine..

 

[Hulk]

My AGM battery has been needing a charge once in a while and it's relatively new. I wonder if I'm having this same issue. I was thinking I had some kind of parasitic battery drain but maybe this is my issue.

 

[DaveInDenver]

My AGM battery has been needing a charge once in a while and it's relatively new. I wonder if I'm having this same issue. I was thinking I had some kind of parasitic battery drain but maybe this is my issue.

What are you using to determine you need to charge it?

 

[Hulk]

What are you using to determine you need to charge it?

When I get a lot of clicking when I start the 80, that's an obvious sign the battery needs to be charged.

 

[RayRay27]

When I get a lot of clicking when I start the 80, that's an obvious sign the battery needs to be charged.

That's what mine is doing. There is a hesitation for a second or two when I turn the key then cranks over.

 

[nakman]

Matt can you measure your voltage? From your ham radio perhaps? Check it before you do anything... then turn the key and check again before you hit the starter. I think normally you should see 12.2-12.4 even when the truck has been sitting for a few days, then at most a .1v drop when you fire up the idiot lights.

 

[DaveInDenver]

When I get a lot of clicking when I start the 80, that's an obvious sign the battery needs to be charged.

That's very low, in fact that battery is in effect completely discharged. Although it might be a side effect of the truck wiring. Small cables or corrosion on terminals in the starter wiring will exacerbate a low battery.

As way of explanation think of a battery as a bucket with a hose going in and a hose going out. You're constantly filling and draining it. For the purposes of lifecycle specification the manufacturer calls one complete fill->empty->fill as a "cycle." That means 100% charged to 0% and back.

Most of the time we don't actually do that. Assuming you do actually full charge (which is not the case, e.g. the voltage bump at hand) you only draw it down with a start say 5%. Then you return it to 100%. Do that 20 times then you have one cycle by equivalency.

The problem here is that if you don't actually get back to 100% each 5% brings the bucket a little lower and next time instead of 100% you start from 97% going to 92%. Next time it's back to only 95% down to 90% and on-and-on until you hit 0% (or whatever is low enough to cause issues anyway).

This creates a more important issue, that being a lead acid battery left at less than 100% charge undergoes a chemical reaction called sulfation. This is where lead crystalizes on the plates and essentially reduces the available lead necessary for the battery to work. Think of it like crud clogging the pores of a sponge, which is more or less exactly what's happening. Build up enough and the battery just stops working but every little bit reduces capacity.

With a regular battery you can reverse sulfation to some extent but with AGM once it starts it's almost impossible to reverse without some damage to the battery. A sulfated AGM can be recovered but there's a trade-off. With a plain battery you hit it with a hard charging that actually knocks the crystals loose and can recombine them partially but this usually boils the electrolyte. Then you can exchange the water and generally only lose some capacity.

Do this with an AGM and it vents, permanently losing electrolyte. So rather than taking a battery with 10% life back to 75% as might be possible with a flooded type you take a 10% life back to 50% because you fix one type of damage by causing another.

That's why is critically important to keep an AGM charged and follow the care and charging profile closely with them. AGMs are temperamental and difficult to keep healthy.

 

[bassguyry]

Hey @RayRay27, just a head's up - @LARGEONE just stopped by my house to pick up a booster I built for him, but it looks like 80s use a larger ATC/ATO fuse size, and my boosters are built for 100s that use the smaller ATM/APM "mini" fuses. Thus, I don't think the booster will fit your 80 correctly.

You're still more than welcome to pick it up, but I figured I'd save you a drive if you want to build your own. Just let me know.

On a related note - it was great to meet you, Paul! I dig that 80, man!

 

[LARGEONE]

Thanks again, Ryland....if nothing else, your contraption (along with Dave's pic above) shows me what to do if I go this route.

I am also going to clean my relay contacts and see if that make any difference. My problem is when my battery is not sitting at 12.7 like it should if fully charged....I turn the key and NOTHING. For some reason there is not enough "juice" to energize the starter relay. If I hold the key for like ten seconds, sometimes it will go ahead and bridge and start. But often, I either have to use my second battery, or put a jump starter on it. As soon as I get full battery power, the truck starts immediately. It does this very hit or miss and is mostly when it is cold and hasn't been driven much. If I drive on the highway for like 20 miles...it never happens after a highway drive. This is what leads me to think my charging voltage is not high enough. But I also suspect something going on with my starter relay...or possibly even the key tumbler ignition switch?

 

[gungriffin]

Thanks again, Ryland....if nothing else, your contraption (along with Dave's pic above) shows me what to do if I go this route.

I am also going to clean my relay contacts and see if that make any difference. My problem is when my battery is not sitting at 12.7 like it should if fully charged....I turn the key and NOTHING. For some reason there is not enough "juice" to energize the starter relay. If I hold the key for like ten seconds, sometimes it will go ahead and bridge and start. But often, I either have to use my second battery, or put a jump starter on it. As soon as I get full battery power, the truck starts immediately. It does this very hit or miss and is mostly when it is cold and hasn't been driven much. If I drive on the highway for like 20 miles...it never happens after a highway drive. This is what leads me to think my charging voltage is not high enough. But I also suspect something going on with my starter relay...or possibly even the key tumbler ignition switch?

Do you have turn the key several times to get it to turn over? If so, you might reach out to Daniel (Inukshuk) and see if he can help explain the problem. He was having a similar issue, but apparently for his truck the issue has to do with the ignition not putting through enough voltage to trigger the starter. The issue was worst when it was cold on the trip we just got back from. For Daniel's issue, the fix is to wire in a relay triggered by the key tumbler.

 

[LARGEONE]

Yep...I have the same problem as Daniel, I believe. I read a thread on MUD about the additional relay...need to read it again and talk to Daniel.

 

[DaveInDenver]

You guys with starter issues, what you describe sounds suspiciously like your contacts and plunger are just worn.

http://www.yotarepair.com/startercontacts.html

https://george4wd.taskled.com/starter.html

 

[LARGEONE]

It’s done it with two different new starters. That was my first guess.

 

[DaveInDenver]

It’s done it with two different new starters. That was my first guess.

Gotcha. Cables and terminals good? Corrosion on the housing causing high resistance? Starters ground through the engine block so it's kind of a convoluted circuit to get current back home to the battery.

It just sounds odd to me. How Toyota built it worked fine for years, right? It shouldn't suddenly develop a design issue after 30 years. Seems like it's a wear and tear issue.

 

[LARGEONE]

Agree Dave on all points. The engine ground strap is on my list to replace as well. I’m just too bad at electrical stuff to truly troubleshoot it.

 

[rover67]

I kinda got fed up with expensive AGM's also. I have switched back to regular flooded lead acid batteries.