Chassis battery charging from shore power w/battery separator?

PhillyGeorge · 04-08-2019, 05:48 PM

Our van has been sitting in our driveway for a few weeks between trips. I checked on it yesterday and found that the chassis battery was dead (I jumped it and it seems fine).

I know this shouldn't be a surprise considering parasitic loads. However, I have had the van plugged into shore power the whole time and thought that my “Blue Sea ML-ACR 7622 Auto Charging Relay” (ACR) would keep not just the HOUSE batteries charged, but also the CHASSIS battery. I now think my assumption about this is probably wrong and would like your comments about how this should work.

FYI, here's my van/electrical setup:
- 2016 Ram Promaster (so the battery is 3 years old)
- Van conversion by Sportsmobile
- House batteries: Four 6V AGM Batteries (approx. 200 AH each for a total of 400 AH wired in series/parallel to provide 12 volts)
- Inverter/ Charger: Magnum MS2000
- Solar panel & charger
BTW, I don’t know very much about electrical systems as you’ll quickly realize.

So here’s my theory about what is happening and why my assumption is probably wrong:

I believed that the ACR would connect the batteries on both sides whenever it sensed a charging source on one side or the other. So, for example, when I’m driving down the road and the alternator is providing power, the ACR will connect the chassis side to the house side so that my house batteries will charge while driving. This is clearly working.

I had also thought that the reverse would occur: With the van parked and plugged into shore power, the ACR would sense the power entering on the house side and close the ACR connection to provide a charge to the chassis battery. My dead chassis battery shows that this is not happening.

Here’s my thinking: Once the shore power charges up the house batteries, the charger shuts off and does not charge the chassis battery as its power is drained due to parasitic loads while there is no matching drop in the house batteries. Does this make sense? If not, why is the chassis battery dead?

(As an aside, I was always suspicious that the chassis battery couldn’t be charged from the charger on the house side anyway, thinking that the charge profile and state of charge of the house vs. chassis batteries could be different. Thoughts?)

OK, so if you’ve made it this far, here is a follow up question:
- Should I use a trickle-charger on the chassis side? Or would this overcharge the house batteries? (I suppose I could override the ACR to force it to disconnect, but it is located under the van in an inaccessible location and I don’t seem to have the remote switch installed – or at least I can’t find it anywhere. Maybe I should get a remote switch installed?)

I know that some of you might recommend just disconnecting the chassis battery between trips. But it is a hassle to get under the floor to do this since the battery is not under the hood. If I could find a trickle-charger that would plug into the cigarette lighter, this would be much easier.

So, any advice you can provide to set me right would be most appreciated.

George

dicktill · 04-08-2019, 07:07 PM

Welcome George!

I have the same Blue Sea 7622 ACR, and it does charge "from either end" as you thought. There is something wrong with yours, or the setup on yours. You shouldn't need to add another trickle charger. And yes the remote switch is a useful accessory.

Your chassis battery may or may not be "done". Try disconnecting it and charging it up with a separate charger. Then disconnect the charger and let it sit for a day or two. Reconnect it to the van and see how it is.

Good luck, Dick

SteveJ · 04-08-2019, 07:59 PM

A battery maintainer would be the way to go vs a trickle charger, if that is the direction you are headed. They are designed to remain connected indefinitely.

Battery Tender by Deltran is a name that comes to mind. Their big ol' factory is near me in Deland, FL. I assume they are still made in the U.S. I use their "mini" for my motorcycles. Good stuff. The plus model even has temperature compensation. Awesome feature set.

gregmchugh · 04-08-2019, 08:24 PM

Since you have solar installed, you might want to consider adding one of these which will automatically charger your chassis battery from the house side solar charging or shore charging. Two models with different charge currents...

LSL Products / LSLProducts.com - Problem-Solving Gear & Gadgets

avanti · 04-08-2019, 08:26 PM

If you are plugged in, there is no point in a separate battery tender. The Trik-L-Start device is specifically intended for this situation, and is install-and-forget.

I don't know about the Blue Sea device.

PhillyGeorge · 04-08-2019, 11:49 PM

Quote:

Originally Posted by dicktill

Welcome George!

I have the same Blue Sea 7622 ACR, and it does charge "from either end" as you thought. There is something wrong with yours, or the setup on yours. You shouldn't need to add another trickle charger. And yes the remote switch is a useful accessory.

Your chassis battery may or may not be "done". Try disconnecting it and charging it up with a separate charger. Then disconnect the charger and let it sit for a day or two. Reconnect it to the van and see how it is.

Good luck, Dick

Thanks very much dicktill. From your response I'm wondering if I should ask Sportsmobile about this (it is a fairly recent build). And maybe they could install the remote switch as well.

George

PhillyGeorge · 04-08-2019, 11:55 PM

And thanks SteveJ, gregmchug and avanti for the info about the Battery Tender and Trik-L-Start.

Avanti, you said, "If you are plugged in, there is no point in a separate battery tender." Does this mean that you think that I should be able to get my existing battery separator (Blue Sea ACR) to charge the chassis battery from shore power?

Thanks again. This is very helpful to hear what others much more knowledgeable than me have to say.

avanti · 04-09-2019, 12:16 AM

Quote:

Originally Posted by PhillyGeorge

Avanti, you said, "If you are plugged in, there is no point in a separate battery tender." Does this mean that you think that I should be able to get my existing battery separator (Blue Sea ACR) to charge the chassis battery from shore power?

No. All I was trying to say is that if you want "battery tender" functionality, and you are leaving your rig plugged in, the Trik-L-Start is a better and more economical alternative than a separate AC battery tender.

As for the Blue Sea ACR: it is an electronically controlled mechanical relay that automatically connects your coach and house batteries if it sees a charge current (13V or more) on either side. If working properly, this will indeed charge your chassis battery whenever you are charging the coach battery. However, it does this by simply shorting them together. IMO, this is kind of a brute-force approach that is not optimal in this situation. It is really meant for boats that have multiple banks of identical batteries. In the case of a B van, the coach and house batteries are likely of different size and age, and quite possibly different chemistry. I wouldn't want my coach charger making decisions on behalf of my chassis starter battery. The Trick-L-Start is essentially a float charger that will gently keep the chassis battery topped off. I think it is a better solution.

PhillyGeorge · 04-09-2019, 12:29 AM

Quote:

Originally Posted by avanti

No. All I was trying to say is that if you want "battery tender" functionality, and you are leaving your rig plugged in, the Trik-L-Start is a better and more economical alternative than a separate AC battery tender.

As for the Blue Sea ACR: it is an electronically controlled mechanical relay that automatically connects your coach and house batteries if it sees a charge current (13V or more) on either side. If working properly, this will indeed charge your chassis battery whenever you are charging the coach battery. However, it does this by simply shorting them together. IMO, this is kind of a brute-force approach that is not optimal in this situation. It is really meant for boats that have multiple banks of identical batteries. In the case of a B van, the coach and house batteries are likely of different size and age, and quite possibly different chemistry. I wouldn't want my coach charger making decisions on behalf of my chassis starter battery. The Trick-L-Start is essentially a float charger that will gently keep the chassis battery topped off. I think it is a better solution.

Got it. I'll have to research the Trik-L-Start to see how it works and how it is installed.

Quick follow up question: You said, "I wouldn't want my coach charger making decisions on behalf of my chassis starter battery." Can I assume that the reverse would be true also. That is, that you wouldn't want the Trik-L-Start (connected to the chassis battery) sending a charge back to the house batteries - meaning that you would want the battery separator to open the circuit so that power is not sent back to the house batteries?

To do this, I would think that I would need to manually disengage the Blue Sea ACR (open the circuit) which means that I would need to have a remote switch installed to do this ??? (I am assuming that the Trik-L-Start puts out more than 13V which would normally trigger the ACR battery separator to close the circuit.)

Thanks again.

George

booster · 04-09-2019, 12:30 AM

The big question would have to be what charger you have and how it is set up. Some chargers have options for charge profile that can be either a "go to float when full" which is normal for lead acid batteries like AGM, or they can be set to "shut off and rebulk when voltage drops" which is more common for lithium batteries.

If yours is set to shut off, you would get exactly what you are seeing, assuming the charger is settable that way.

avanti · 04-09-2019, 12:42 AM

Quote:

Originally Posted by PhillyGeorge

Got it. I'll have to research the Trik-L-Start to see how it works and how it is installed.

Quick follow up question: You said, "I wouldn't want my coach charger making decisions on behalf of my chassis starter battery." Can I assume that the reverse would be true also. That is, that you wouldn't want the Trik-L-Start (connected to the chassis battery) sending a charge back to the house batteries - meaning that you would want the battery separator to open the circuit so that power is not sent back to the house batteries?

To do this, I would think that I would need to manually disengage the Blue Sea ACR (open the circuit) which means that I would need to have a remote switch installed to do this ??? (I am assuming that the Trik-L-Start puts out more than 13V which would normally trigger the ACR battery separator to close the circuit.)

Yes, I don't think that the ACR and Trik-L-Start are mutually compatible. I think your analysis about the Trik-L-Start activating the relay is correct. That wouldn't be good. In fact, a Trick-L-Start is typically wired across the isolation relay, such that when the relay closes, its input and output are shorted and so it is effectively removed from the system. This in turn would cause the ACR to open, which would put the Trik-L-Start back into the system. Rinse and repeat... Looks to me like you would end up with an oscillator. Not good.

So, I think your choice is to leave it as is (after first figuring out why it isn't working), or removing the ACR and replacing it with a dumb isolation relay and adding the Trik-L-Start.

PhillyGeorge · 04-09-2019, 02:06 AM

Makes sense. Thanks for the additional info.

George

hdevera · 04-14-2019, 08:59 PM

My two cents from a similar issue: I bought a new battery, since mine would no longer hold a charge well. Now I use a small solar charger (7.5 Amps max) connected to the cigarette lighter (which is on even after ignition is turned off), and trickle charge the chassis battery. Solar panel is left on the windshield when storing even for a few days. I have a MB sprinter and there is quite a bit of parasitic discharge. Sprinters seem to be designed to be used frequently.

PhillyGeorge · 04-15-2019, 04:41 PM

FYI, my problem appears to be solved. There is a red control wire coming from the Blue Sea ACR that is used to add a separate control switch. However, Sportsmobile had wired this to the chassis power system in a way that defeated the bi-directional sensing for the ACR. I just cut this wire and it looks like it is now working fine and charging the chassis battery from shore power.

Thank you to all who responded to my questions.

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