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Charging rates

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timtune

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I have a question about my Roadtrek campervan (1998 Dodge 3500 based) and I know this is a clever group so here goes.

I have two lead acid batteries providing "shore power". They don't appear to charge as well on the road as they do when the van is plugged into 120VAC.
At rest they read 12.5V. Plugged in (120vac) I'm getting 13.1 but only about 12.7 with the engine running, revved up a bit got it to 12.9. The Squeeze was working the gas peddle so I'm not sure how hard she was pushing. I'm tempted to run some extra wire so I can get a good "going down the road" reading.

Is it likely there are two separate charging systems depending on being plugged in or engine running?

If so and the the 12v charging system is not performing 100% would there be much to "service" or am I likely replacing?
 
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One is charging through the alternator and the other way is through a converter. If that makes any sense

Alternators can only push so much
 
Two completely different charging systems. One is alternator powered by engine, the other is a battery charger powered by 120V.

How far away from engine are batteries? Are both similar, or one much further? Were you measuring battery closest to engine or furthest? Measure voltage close to engine (battery or fuse box) and see what that is. If that's high and voltage at your remote batteries is low, you either have bad connections or wire too small. If that is the same voltage as distant batteries (or close), wiring to the remote batteries is fine and your alternator may be maxed out. Charging three batteries (two of which may be substantially low) and running the vehicle is a lot. Charging batteries slowly isn't a bad thing. It all depends on the requirements. If you want them full again between sites and drive for a few hours, I suspect you're ok. If you want to idle the big engine to charge the batteries in camp, I suspect you'd save a ton of fuel with a generator and charger.
 
Just dropped the van off for an oil change after which I thought I should do a check on the "engine" battery (One batt for the truck and 2 more for shore power) to compare.
I'm not sure if the the shore power is charged directly from the alternator or if the alternator feeds power to a separate shore power charging system.
 
Original shore power battery is factory located at the rear. I hooked a second battery in paralell close to the first (maybe 3 feet of cable between them).
I'd have to do some looking to figure out where the shore power is fed from the alternator.
 
timtune said:
Original shore power battery is factory located at the rear. I hooked a second battery in paralell close to the first (maybe 3 feet of cable between them).
I'd have to do some looking to figure out where the shore power is fed from the alternator.
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Measure voltage close to engine somewhere and report back. It may just be high draw and long undersized wire. The 120v charger will be located very close to batteries so it can get away with small wire.
 
GreyGhost said:
Charging three batteries (two of which may be substantially low) and running the vehicle is a lot.
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Part of the problem is while on the road "charging" we have the fridge in 12V which is quite a draw I'm told.
 
You may want to check the alternator's output rating and potentially upgrade it to a higher capacity if you have a lot of stuff running while driving.
 
timtune said:
Part of the problem is while on the road "charging" we have the fridge in 12V which is quite a draw I'm told.
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Fridge is probably 10 amps or so. I don't know for sure but alternator output is probably 90 amps or so (roadtrek may have put in a bigger one?). 10 amps for each battery charging is another 30 amps. Something like 10 amps to keep the engine running. 10 amps for headlights. Blower fan for interior HVAC could be up to 30 amps. So that's about 90 amps already.

Here is a decent roadtrek reference (although for slightly newer models).

Checking charging from engine/alternator Roadtrek 210 - Class B Forums

I took a look at the archives and have not found a clear answer to my question which is. Do I have to disconnect the positive and negative lead from the engine to my house batteries in order to check
www.classbforum.com
 
Alternator tries to charge all 3 when driving. There is a isolation solenoid that turns on when the engine is started to charge the house battery. You should have 13.5 v minimum usually over 14 at the alternator and similar at the house battery when running. Those solenoids are notorious for failure. Is it a old 3 way fridge propane/electric those use a ton of power on 12v I would run it on propane when driving. Ours has a newer 12v compressor fridge that uses very little power in comparison.
The way those old fridges cool is adsorbtion and is 15 amp constantly running a heating element to cool the fridge they don't cycle on off.
By comparison the new ones use 21 ah per 24 hrs. The old ones use 360 ah in 24 hrs.

Sent from the future
 
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Scuba Steve said:
Alternator tries to charge all 3 when driving.
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It shouldn't... it SHOULD prioritize the "under hood" battery, at least that's how it was designed. That's one of the reasons it has isolators.

OP: This is something that is too big to try to explain it here... you might have a charging problem, or you might have a load problem. You need to isolate the "under hood" battery, and test the charging system... then remove all load from the "shore batteries" and see if they charge... but there is an isolation circuit between the two that can go wrong.
If that checks out, you have too much load.
Only one alternator?
Your batteries SHOULD be 12.7 MINIMUM at rest... have you tried charging the batteries alone? If you have been running them at less than 12.7 you have damaged the batteries and maybe they won't charge. The batteries need 13.2v, or more, to charge fully
Are your "shore batteries" deep cycle? (They SHOULD be. Deep cycles will take a LOT more abuse... which as you can see, you're abusing those batteries).
How big (how many amp/hours) are the batteries?
... and you local garage will be lost trying to figure this out, and the local RV garage will charge you a small fortune (if it was a 2023 model they'd charge you a LARGE fortune)... I suggest you find an auto electric shop. The only auto electric shop I can recommend is Start Auto Electric, but they're downtown Toronto. RVs can get tricky.
If you want to try to fix this yourself, I'll try to help, but from your post I can tell you're in well over your head.
 
bitzz said:
It shouldn't... it SHOULD prioritize the "under hood" battery, at least that's how it was designed. That's one of the reasons it has isolators.

OP: This is something that is too big to try to explain it here... you might have a charging problem, or you might have a load problem. You need to isolate the "under hood" battery, and test the charging system... then remove all load from the "shore batteries" and see if they charge... but there is an isolation circuit between the two that can go wrong.
If that checks out, you have too much load.
Only one alternator?
Your batteries SHOULD be 12.7 MINIMUM at rest... have you tried charging the batteries alone? If you have been running them at less than 12.7 you have damaged the batteries and maybe they won't charge. The batteries need 13.2v, or more, to charge fully
Are your "shore batteries" deep cycle? (They SHOULD be. Deep cycles will take a LOT more abuse... which as you can see, you're abusing those batteries).
How big (how many amp/hours) are the batteries?
... and you local garage will be lost trying to figure this out, and the local RV garage will charge you a small fortune (if it was a 2023 model they'd charge you a LARGE fortune)... I suggest you find an auto electric shop. The only auto electric shop I can recommend is Start Auto Electric, but they're downtown Toronto. RVs can get tricky.
If you want to try to fix this yourself, I'll try to help, but from your post I can tell you're in well over your head.
Click to expand...
Maybe a road trip?
 
bitzz said:
It shouldn't... it SHOULD prioritize the "under hood" battery, at least that's how it was designed. That's one of the reasons it has isolators.

OP: This is something that is too big to try to explain it here... you might have a charging problem, or you might have a load problem. You need to isolate the "under hood" battery, and test the charging system... then remove all load from the "shore batteries" and see if they charge... but there is an isolation circuit between the two that can go wrong.
If that checks out, you have too much load.
Only one alternator?
Your batteries SHOULD be 12.7 MINIMUM at rest... have you tried charging the batteries alone? If you have been running them at less than 12.7 you have damaged the batteries and maybe they won't charge. The batteries need 13.2v, or more, to charge fully
Are your "shore batteries" deep cycle? (They SHOULD be. Deep cycles will take a LOT more abuse... which as you can see, you're abusing those batteries).
How big (how many amp/hours) are the batteries?
... and you local garage will be lost trying to figure this out, and the local RV garage will charge you a small fortune (if it was a 2023 model they'd charge you a LARGE fortune)... I suggest you find an auto electric shop. The only auto electric shop I can recommend is Start Auto Electric, but they're downtown Toronto. RVs can get tricky.
If you want to try to fix this yourself, I'll try to help, but from your post I can tell you're in well over your head.
Click to expand...
Thanks for the vote of confidence. I'm off to find the isolator.
 
bitzz said:
It shouldn't... it SHOULD prioritize the "under hood" battery, at least that's how it was designed. That's one of the reasons it has isolators.

OP: This is something that is too big to try to explain it here... you might have a charging problem, or you might have a load problem. You need to isolate the "under hood" battery, and test the charging system... then remove all load from the "shore batteries" and see if they charge... but there is an isolation circuit between the two that can go wrong.
If that checks out, you have too much load.
Only one alternator?
Your batteries SHOULD be 12.7 MINIMUM at rest... have you tried charging the batteries alone? If you have been running them at less than 12.7 you have damaged the batteries and maybe they won't charge. The batteries need 13.2v, or more, to charge fully
Are your "shore batteries" deep cycle? (They SHOULD be. Deep cycles will take a LOT more abuse... which as you can see, you're abusing those batteries).
How big (how many amp/hours) are the batteries?
... and you local garage will be lost trying to figure this out, and the local RV garage will charge you a small fortune (if it was a 2023 model they'd charge you a LARGE fortune)... I suggest you find an auto electric shop. The only auto electric shop I can recommend is Start Auto Electric, but they're downtown Toronto. RVs can get tricky.
If you want to try to fix this yourself, I'll try to help, but from your post I can tell you're in well over your head.
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Nope no isolation just a solenoid my 2022 is the same way.

Sent from the future
 
timtune said:
Thanks for the vote of confidence. I'm off to find the isolator.
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99 percent sure you won't have one. I know my 2022 has nothing but a solenoid that connects the banks when the engine is running. Do you have a boost switch it so press it and you should hear the click of the solenoid.

Sent from the future
 
timtune said:
Thanks for the vote of confidence. I'm off to find the isolator.
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Nothing personal
I ran the shop at Dundas Alternator and Starter for years and have seen what many professional techs are capable of: NOT MUCH. I've worked on lots of isolated systems... and they CAN get complicated.
And now you say you're going to start throwing parts at it with no tests... that's a bad omen
You said in your original post that you were considering running new wires to the cabin batteries... without knowing what's wrong... that's a bad omen
 
bitzz said:
And what controls the trigger on the isolator relays/solenoids? Every one I have seen has Zenors that shut off the cabin batteries when the charge gets below 13.2v
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The alternator turns on the solenoid as soon as the alternator is turning at speed it outputs 12v. Once the engine is running it sends 12v to the solenoid to close it. Very simple system the diode isolation hasn't been used for decades. My guess is the heat and voltage drop from the isolator is why they are no longer used. I also have a 60amp 12 to 12 charger in mine for the second lithium bank that runs the air conditioner. But his won't have 12v ac

Sent from the future
 
bitzz said:
And what controls the trigger on the isolator relays/solenoids? Every one I have seen has Zenors that shut off the cabin batteries when the charge gets below 13.2v
Click to expand...
This is the solenoid on mine it is under the van in a box.you can also see the disconnect solenoid for the interior lights etc.
7a32b9dd208b139e2ebafee3a4d81be6.jpg


Sent from the future
4bfca49946b492892edcf5217029ceeb.jpg
 
How 'bout this:
Different manufacturers use different systems, and trying to diagnose and repair said systems require a decent overview of function.
If you can't look over the spaghetti wiring like in the above pictures, identify the components and function of those components and troubleshoot what you're looking at... you're gonna have a bad time
IE: Steve: I'm pretty sure the black box with multiple wires in the foreground of the last pic is a charge controller, that will isolate the cabin batteries if the voltage drops... it might not be, but it sure looks like how I wire charge controllers. You want an "auto" isolator so the cabin batteries don't flatten your underhood battery... so the truck starts after a hard night of partying with the stereo on full blast and the beer fridge being opened every 35 seconds and you were too drunk to start the genny and you wake up, in a stupor, to 5 dead batteries... been there done that, fixed the isolators
 
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