Weird charging issue, E350 Ambulance... House batteries.

[Bikersmurf]

Went out and started the rig this morning without any problem, the two starting batteries started the 7.3 diesel as they should. The stock Voltmeter showed strong batteries which I confirmed with a digital multimeter.

The battery idiot light was on and stayed on for my 15 minute drive. An hour or so later, truck started again, no problems, the idiot light was still on.

When I got to my destination, I had a chance to look into it. I'd had the fridge running off the house batteries for a few days and they were dead <6V. The Battery isolator did its Job and protected the starting batteries. So why wasn't the alternator not charging? The answer, the new alternator wasn't getting enough voltage to excite it. The solution... To jump start the house batteries, thereby exciting the alternator, and giving it the power to charge the batteries.

It's not a big deal... I know how to resolve the issue. But anyone know how to fix it so it doesn't happen again?

Possible solutions:
1) ditch the diode type battery isolator.
2) switch the power source for the Voltage regulator... Not sure how.
3) wire in a momentary switch to trigger a solenoid to bypass the isolator.
4) wire in a manual switch in parallel to the isolator.

Concerns:
1) would connecting two starting batteries to two dead house batteries drain them too much to start the rig before all four batteries are recharged?
2) if the wiring is changed, and and alternator is excited by the starting batteries, could running down the cranking batteries cause the same problem?
3) would ACR battery isolator have other inherent problems? Ie. four batteries without enough juice to crank a 7.3 diesel in cold weather?

 

[flightcancled]

What voltage are your starting batteries showing when you are driving around? The ACR is an elegant solution and will increase performance, but they don't start charging the house batteries until they have had a voltage over 13.5 for 2 minutes. Or at least that is how my Blue Sea one works.


Sent from my iPhone using Tapatalk

 

[DiploStrat]

Two serious suggestions:

-- Remove the diode isolator, and,
-- Get a Moderator to move this to the 12v Forum.

Both will give you much better results.

 

[dwh]

Possible solutions:
1) ditch the diode type battery isolator.
2) switch the power source for the Voltage regulator... Not sure how.
3) wire in a momentary switch to trigger a solenoid to bypass the isolator.
4) wire in a manual switch in parallel to the isolator.

Concerns:
1) would connecting two starting batteries to two dead house batteries drain them too much to start the rig before all four batteries are recharged?
2) if the wiring is changed, and and alternator is excited by the starting batteries, could running down the cranking batteries cause the same problem?
3) would ACR battery isolator have other inherent problems? Ie. four batteries without enough juice to crank a 7.3 diesel in cold weather?

Whack. I've never actually seen that problem before. But, I don't use the diode-type isolators, I've always just used a split-charge relay.

Which is the solution I'd go with - #1. And by the way, if you went with solution #3 - you'd have a split charge relay and wouldn't need the diode-type isolator anyway if you just energized the solenoid from an ignition circuit.

As for the concerns...

1) Very much doubt it. Don't think I've run a house battery down to 6v, but I know I've gone down to 8v and didn't have the problem. It takes a while for current to transfer from the cranking battery to the house battery, so with a dumb solenoid, when you turn the key on, and start the engine immediately, I've never had a problem where a dead house battery prevented it from starting - or even slowed it down.

Even if current were flowing from one to the other at a rate of say...240 amps to make the math easy...

240a per hour
240 / 60 = 4a per minute
4 / 60 = 0.07a per second

Though of course, it won't flow at that rate, because a dead battery has a very high resistance. So in the time it takes to start the truck, damn near nothing is going to move from the engine battery to the house battery.


2) I have left my lights on and run down the cranking battery and had to jump off the house battery. Didn't have the problem - alternator worked fine.

3) Yea, as flightcancled said, an ACR isn't going to tie the batteries for starting. It'll wait till the cranking battery has had a chance to recharge the little bit it took to start the truck. See my math above - if your starter were to draw 240a, then running it for 10 seconds (make a starter sound and count off 10 seconds - that's LONG time for a starter to run) would drain the cranking battery .7 amp*hour.

With a dumb solenoid...the truck I have now (460 engine), with stock battery cables it would not self-jump from the house battery. I had to go with larger cables from each battery to the solenoid (I just went to the welding shop and had them make me some out of 1/0 welding cable) for it to be able to self-jump.


I use a dumb solenoid. I recommend that over a diode-type isolator. But in my opinion, an ACR can be a better solution, depending. For the problem you just described, an ACR would be better since it wouldn't tie in the house battery until the charging system was already up and running and the cranking battery was topped up a bit.

But...some will untie the batteries if voltage falls too low - such as when winching, which is exactly when you don't want the batteries to isolate. So for a truck with a winch, I'd want an ACR with a bypass switch so I could lock it on when winching. And of course, you'd want a bypass switch anyway if you wanted to be able to self-jump.

But really, self-jumping is something that you need to do about as often as you need to jump-start your truck anyway. Like what? Once or twice every 10 years? I rigged my truck so it *can* self-jump, and I've used it a couple of times. In my opinion - it wasn't worth the time, effort and money. I carry jumper cables anyway which would work fine for the extremely rare times I'd need to self-jump.

And if you run your house battery down - you're probably not going to jump off that anyway.


For the way it sounds like you use your truck - I'd go with the ACR to make protecting the engine battery the main priority.

 

[Bikersmurf]

After starting the truck three times and 1/2 an hour driving, the starting batteries were down to 12.3 V.

I know an ACR will be the way to go when budget permits, and for the most part I was wanting to let people know about a weird problem I'd never seen before. I've bump started gassers and never had any trouble getting the alternator to charge... With diesels, the problem could be much worse.

The rig is already set up with a 'Sure Start' circuit to self jump off the house batteries... It was an Ambulance and lives could depend on getting it running on a 30 below morning. It only works, however, when there is enough power in the house batteries to power the solenoids.

It sounds like I'm over thinking it... Sometimes it helps to have an outside perspective... Electronics class was a long time ago.

 

[dwh]

Well if you have a solenoid setup already, you could just power the solenoid from an ignition circuit instead of the house battery and you'd have a regular split-charge relay. Lotta people have used them for a lotta years without problems.

Dunno if that would solve the alternator problem though - like I said, never seen that one before.

Guess if you had to, you could rig the power for the solenoid from the engine battery through a switch and manually tie in the house battery after you're sure the alternator is producing. Hrmmm....I'd still power it off an ignition circuit, just in case I brain farted and forgot to turn off the switch - then the solenoid would be disengaged whenever I turned off the key.

 

[Mwilliamshs]

Your alternator should be excited by the start battery or really, the van fuse panel. If the house batteries are involved something is amiss. The diode isolator is not ideal. A VSR, voltage sensing relay, is better and not expensive but if what you have WAS working, something has changed.

My theory is your isolator has failed shut. The house and start battery are connected and the isolator is constantly burning voltage. This pulled system voltage below what's needed for excitation and then pulled the start battery(ies) down due to no charge whilst the house batteries were drained by the fridge etc.

 

[Bikersmurf]

An interesting theory, but the diode isolator is still working as designed. The OEM voltmeter is wired to read the starting battery voltage, and the idiot light shows alternator output.

In an OEM setup, the alternator is powered by the van panel... But this has been highly modified and then monkied with for 7 years after retirement from ambulance duty. I'm sure it would be easy enough to switch where the alternator is wired to... If I knew enough about the 50+ pounds of extra wiring. For the time being, I'll know if the house batteries are totally dead, I'll need to jump them to excite the alternator. And, I'll save up my pennies for a 200 + amp voltage sensing charge controller... So I don't cook my starting batteries when I'm recharging the deep cycles.