Alternator not charging house batteries?

scout63

New member
Just purchased a 2013 Roadtrek RS on the 3500 chassis. It has 2 6 volt agm batteries wired in series under the hood for the house batteries. These batteries are constantly drained and will not start the generator. When I plug into shore power, the batteries charge and the generator will start, but the batteries don't seem to be charging while the vehicle is being driven.

The parasitic draw with the battery switch off is 0.5 amps. When I hook shore power up, I am getting about 14.6 volts across the two batteries. When I remove shore power, and start the engine, I am only getting 12.6 volts, which is also the resting voltage of the battery bank. Hence I am not getting any charge from the alternator (correct?).

I'm guessing the Eaton battery separator is at fault. Do I just replace it, or is there a way to actually test the separator? Is 0.5 amps enough to drain these batteries over 24 hours such that they won't start the Onan generator? Any other suggestions?

Thanks!
 

autostaretx

Erratic Member
Enough people are finding their RV-supplied isolation relays to have failed that it's almost a given to replace it (with a Cole Hersee 200 amp unit).

You can certainly test the separator with a voltmeter ... look at both each big stud's voltage above the frame AND measure between the two studs when it's supposed to be joining the batteries. In the "join" state, you want the voltage between the studs to be as low as possible. If you see a volt or more between them, the relay isn't doing its job. Even a half volt is kind'a excessive.

When the isolator is NOT operating the voltage between the studs should match the voltage difference between the two banks and the frame.

So, with "engine off, key out", if the house batt tests at 12.7, and the starting batt tests at 12.4, the stud-to-stud voltage should be 0.3v
With "eingine on, batts joined", the stud-to-stud would be optimally 0v , and the starting and house batteries both being at alternator (i.e. starting batt) voltage ... something along the line of 13.6 to 14.2

Is your 0.5 amps parasitic on the starting side, or the house side?
It's very excessive for the starting side. (which should be 0.05 amps)

--dick
 
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scout63

New member
So, upon further inspection, it looks like they had the 2 wires installed backward- main lug on the separator wired to house, and aux lug wired to starting battery. Not sure that should actually matter, but I switched the leads.

When I started the RV, I was getting about 14.3 volts to the starting battery and 12.6 to the house batteries (same voltage as when the RV wasn't running). I then wrapped on the separator with a wrench and the voltage jumped to 14.3 on the house (same as the starter). I guess I have a bad separator, or at least a dirty contact.

Which Cole Hersee unit do you recommend?

Thanks for the help on this
Greg
 

autostaretx

Erratic Member
I was thinking along the lines of this: $43 Cole Hersee 24213 12V 200A Continuous Solenoid
Such as here: https://www.amazon.com/Cole-Hersee-24213-Continuous-Solenoid/dp/B005K2429I/?tag=sprintersou02-20

No, it's not their "smart" $108 solenoid .. this one doesn't try to out-smart you, it just listens to the "please connect" signal.

Many people like the BlueSea ACR (automatic charging relay) ... it senses both sides for charging voltages and joins if it sees them. The problem with that is you'll be charging your starter battery from your house system, as well as vice-versa.
If your batteries are different chemistries (say AGM and flooded lead acid) one side will be slightly unhappy.

--dick
p.s. the above amazon link includes the "help the sprinter forum" associate tag.
 
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scout63

New member
Ok- looks like a great, simple solution. So I control this off of a positive signal from the ignition key. Would you recommend running it through a rocker switch, such that I can manually disconnect the batteries while the van is running? I don't have a schematic of my RV electrical system and I'm a newbie to all of this- would this manual approach interfere with charging from shore power or with the Onan genset?
 

BobLLL

Member
Here is an excellent description of how to replace the battery separator with a Blue Sea unit:
http://roadtreklife.blogspot.com/2015/12/battery-isolator-upgrade-to-blue-sea-ml.html
More comments here:
https://sprinter-source.com/forum/showpost.php?p=462168&postcount=32

I replaced my battery separator with a Blue Sea relay a couple of years ago and am pleased with it. I had a Cole Hersee relay in an earlier rv. It worked, but I would not use one again. The two way automatic operation of the Blue Sea is much better. There is no problem with charging the starter battery with the shore power. In fact it is an advantage: Plugging in shore power at least once a week between trips will keep all the batteries well-charged. The Blue Sea is more expensive, but well worth it in the long run.

If you want to learn more about the RT charging system, and diagnose your separator further before taking action, there is a lot more info available. You will see at least one other endorsement of the Blue Sea by someone who actually have one installed in a Roadtrek like yours.
https://sprinter-source.com/forum/showthread.php?t=47659
 

autostaretx

Erratic Member
Ok- looks like a great, simple solution. So I control this off of a positive signal from the ignition key. Would you recommend running it through a rocker switch, such that I can manually disconnect the batteries while the van is running? I don't have a schematic of my RV electrical system and I'm a newbie to all of this- would this manual approach interfere with charging from shore power or with the Onan genset?
Run your VIN through https://www.datamb.com/ to fetch your "datacard" (things MB built into your Sprinter)

See if you have the EK1 option.

If you do, look for this under the driver's seat:



which is item (4) in this diagram:



(just behind the rear of the fuse panel).

The "D+" (smallest) post is *specifically* to operate the coils of isolation relays. It goes to +12v when the alternator is running. You'll also need to run a small wire from the Cole Hesee's 2nd small post to the Sprinter's frame (proving the negative for the coil).

If you don't have the EK1 option, you could use whatever the RV was already using to drive its separator relay.

By using the "D+ switched relay" you don't interfere at all with any shore-based charging system. (unless you're running the Sprinter's engine at the same time)

A BlueSea ACR *would* join the two if it saw the shore-powered charging voltage on the house side (but you can buy a version that has a separate wire to tell it to NOT join).

--dick
p.s. i'm not really against the BlueSea answer, as BobLL is an example, many members are very happy with their BlueSea ACR. It's just that sometimes i prefer to have systems that don't unexpectedly do things.... for example: if you switched to Lithium house batteries, their "resting" voltage can be high enough to trigger the ACR. If you didn't recall that, you'd wonder why things were acting weird.
 
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BobLLL

Member
The blue sea unit fits in the same place as the original, uses the same wiring, and works better than the original. The job will be done in a fraction of the time.
 

Mein Sprinter

2010 Roadtrek SS Agile
The blue sea unit fits in the same place as the original, uses the same wiring, and works better than the original. The job will be done in a fraction of the time.
Hi BobLLL...I don't need the higher cost BlueSea, just the basic 120amp one. Again a awkward question for my poor electronics mind.. The 120a one is hooked up the same way as the current Sure Power ACR my 2010 Roadtrek has.

BlueSEA-(A)House----(B)Start..... then the ground (spade) on the BlueSea ACR? What's the the "start isolation" and "LED" for?

cheers...
 

autostaretx

Erratic Member
The "start isolation" is to command the BlueSea to *not* join the batteries during the crank-to-start period.

It avoids trying to draw too much current through the BlueSea.

--dick
 

BobLLL

Member
I am camping now, with limited internet. If you have any further questions, I should be able to reply on Saturday.
 

Mein Sprinter

2010 Roadtrek SS Agile
I am camping now, with limited internet. If you have any further questions, I should be able to reply on Saturday.
Thank you BobLLL..some of your friends have answered my questions for you. Enjoy your camping. :thumbup::cheers:

Just for fun: have you ever tried this Sky Roam Solis-Super fast portable WiFi extender?

cheers...
 

BobLLL

Member
Mein,

I had never heard of the Sky Roam Solis unit before. I do have a ZTE Z288L Hotspot, with service via Straight Talk prepaid cellular. It works wherever there is a Verizon signal, but the speed of data transmission varies greatly depending on location. I think the same would be true of any portable unit:none of them can be any faster than the speed the nearest cell tower is able to able to handle. Which seems to depend on the number of users who are trying to access that tower. For example, reception in campgrounds near busy highways or in busy resort areas has often been slower than the speed in fairly remote camps with few people around and a fairly weak cell signal.
 

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