Voltage drop

[MDH33]

I've had an ongoing problem with voltage drop in my '85 FJ60. Voltage is fine while running and idling, except when I turn on the headlights, or use the blinkers at idle, I drop below 12V. I have a newish alternator and regulator, upgraded IPF headlights and relayed ARB headlight harness connected to the battery and I have tried the fused direct connection from alternator to battery. Any ideas what to look for? Or is the alternator just not up to the task?

This causes an issue with my National Luna dual battery setup. When the voltage drops, it turns off the solenoid to the second battery, so it's not getting a charge and gets really low after a few days. Ive disconnected the second battery from the system for the time being.

Any tips appreciated.

 

[DaveInDenver]

When you say fine, how fine is it? In other words, what's the voltage right after you start and after driving for a while?

My first suspicion would be alternator or voltage regulator is kaput or if it's an adjustable type it's set way too low.

Could be something simple, too, broken wire, corroded terminals, bad grounds causing the output to be low on the alternator.

You need the battery voltage to be around 14 V with the engine running to charge the battery and below about 13.5 V you're never going to fully charge the battery. With the headlights and running lights on the charging system even in an old Cruiser should be at least sufficient for the battery not to run down. It's not going to run LED bars and big stereos, though, so you may have to turn down the double dime boom box when roll in your hoopty.

 

[SteveH]

What's your idle speed? Sometimes just bumping up the idle a small amount will cause much better alternator output. 650 is too low, IMO, when you start turning on the headlights and heater fan.

 

[MDH33]

Thanks for the responses, Dave and Steve.

I did some quick measurements:

Battery cold before starting: 12.35V
Cold Start & Idle ~500rpm: 13.75V
W/ lights on: 12V

1 click on choke, still cold ~700rpm: 14.34V

Slight increase in RPM seemed to help, so I warmed it up, reset idle to ~750: 14.34V

stayed consistent at various RPM's.

With lights on at ~750 rpm: 14.04
Lights and heater at~750rpm: 13.34

So, it seems like increased idle helped a lot! Still a little low with everything on, but high enough to keep my solenoid open, which is great. Wondering if there's anything else to do? all grounds and connections look good. Carlton upgraded a lot of battery and ground connections with giant guage wires prior to my purchase.

Is there any reason I couldn't connect the headlight harness to second battery? I don't have much on that battery now, just compressor, fridge and radio (Ham, not a giant sub-pumping double dime boom box )

 

[DaveInDenver]

Just some random thoughts.

That 12.35V is very low, indicates a battery that is only charged to about 75% or could indicate a battery that is failing. If your battery is in bad condition it could be dragging the charging system down giving a low reading.

The other running voltages aren't terrible. That 14.34V is what you want to see at idle and a little higher than that wouldn't hurt anything.

Dropping below 14V with the headlights isn't unusual but 13.34V is low enough that you won't be charging. Probably not draining the battery much either, but it's close. You need about 13.6V or higher to charge even a little and that will be a very slight trickle/float.

I wouldn't connect the headlights to your aux battery. If your voltage does drop enough for the solenoid to open you'll just be drawing down your back up. From the sound of it that's actually in better condition and I would keep it protected as back up in case your main or charging system goes bad. You can then start a few times and run long enough to get off a trail or back to town, for example.

If Carlton did the upgrades then I wouldn't expect a cable or ground issue. FWIW Imelda also got some upgraded battery cables.

Things you can do are, like Steve says, make sure your cold and hot idles are set high enough. I'd also consider looking for a smaller alternator pulley to get the RPM of it up. You'll probably never get the engine RPM up high enough on a 2F to worry about spinning an alternator too fast...

 

[MDH33]

I think the low battery could be related to my 3 mile commute in stop and go traffic and that I have been starting it a lot while fiddling with it but not driving long enough to charge properly. I have it on a trickle charge now, so I'll do measurements again tomorrow night. I'll make sure to drive it longer than 3 miles too. The battery is a 2 year old red top, so hopefully still good. I had it inside all winter on a battery maintainer while the 60 was in hibernation.

Thanks Dave, and Imelda starts and runs flawlessly, every time!

 

[DaveInDenver]

Since it's a Red Top that 12.35 is even worse. Even a properly functioning stock charging system needs to get a periodic assist to keep AGM batteries healthy.

Let it sit on a charger for a couple of days, then let it sit for an hour or two and see what the voltage is. Ideally you'll see about 12.7 or 12.8 volts, which is good for an AGM.