Charge chassis battery from shore power? (w/ battery separator)

[geo2015]

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

[86Scotty]

Most Blue Sea ACRs are bidirectional, which makes me wonder if you don't have a problem with yours or perhaps a breaker turned off/fuse blown. Scalf should be along any time to go through this with you. I know the 7610 I have used is bidirectional. I would think the 7622, and for that matter anything SMB used on a recent build, would be too.

[geo2015]

Originally Posted by 86Scotty

Most Blue Sea ACRs are bidirectional, which makes me wonder if you don't have a problem with yours or perhaps a breaker turned off/fuse blown. Scalf should be along any time to go through this with you. I know the 7610 I have used is bidirectional. I would think the 7622, and for that matter anything SMB used on a recent build, would be too.

Thanks 86Scotty. Sounds like you think that maybe the chassis battery should get a charge from shore power. I'm very interested to hear what others think as well.

George

[Scalf77]

George,
If hooked up correctly or working correctly the 7622 should work just how you think it should. If show power or solar brings the house battery up above 13.2 volts it should connect and charge the chassis battery.

There appears to be some confusion in how sportsmobile has wired these up, which may be leading to your problem. The first thing to check is how the ACR is wired up. In its simplest form with out the remote switch it should look like this.


The only wire from the control bundle that needs to be wired is the black wire to ground. My diagram shows a 10 amp fuse inline, this could be considered optional, and Sportsmobile probably has not added the fuse. All the other wires should be tied and isolated. Especially the red control wire. In this mode the the 7622 will operate in a bidirectional mode, and connect depending on the voltage. It is possible that sportsmobile wired the control wire to the key switch to simulate start assist. If the wire has a fuse on it try pulling the fuse and see if your ACR will connect when plugged in and charging. For the ACR to work in auto mode the Red wire needs to be floating, 12 volts will connect the batteries, ground or low potential will disconnect the batteries.

I do recommend to wire in the control switch, you can buy it separately. It would look like this



The #2146 is ON-OFF-ON switch, leave it in the middle and it will be off, the control line will float, in the up position it connect to 12 volts forcing the ACR to connect, and last in the down position it connect to ground and forces the ACR to disconnect. The yellow wire is for the LED indicator in the switch, it will light when connected and be off when disconnected. It also will perform some blink codes for error situations

Hope this helps.

-greg

[geo2015]

This is so helpful. Thank you very much !!!

This will take me some time to digest and figure out the wiring, especially since the ACR is installed under the van in a hard to access location. I'll let you know what I find out.

Thanks again.

George

[AndrewInSeattle]

I haven't needed to try this yet, but the owner's manual that Sportsmobile West provided for our 2017 build said somewhere that you can jump-start the chassis battery from the house battery by holding the key in the ignition position for 10 seconds. I got the impression that the rest of the time, it was unidirectional, to avoid draining the chassis battery if you left the refrigerator running.

[Fitz]

Originally Posted by AndrewInSeattle

I haven't needed to try this yet, but the owner's manual that Sportsmobile West provided for our 2017 build said somewhere that you can jump-start the chassis battery from the house battery by holding the key in the ignition position for 10 seconds. I got the impression that the rest of the time, it was unidirectional, to avoid draining the chassis battery if you left the refrigerator running.

There is a pretty good discussion on this topic, including the differences between the approach Austin and Fresno each take, over in my build thread.

http://www.sportsmobileforum.com/for...-16293-62.html Start at Post #617 on page 62, the discussion continues until Post #644. There will be more once I make the changes I have planned, hopefully in the near future!

[geo2015]

Fitz and AndrewInSeattle: Thanks for this info. Wow, it is quite nuanced how SMB installs these systems. I will read the posts you referenced to try to educate myself.

In the meantime, here's what I found in response to the info provided by Scalf77:

I did some digging under the van to find out how the ML-ACR is wired and it is a bit different from the diagram you attached. BTW, the ACR is located underneath the van very close to the chassis battery. This doesn’t seem ideal in terms of weather protection. There does appear to be slight weathering of the main connectors.

Also, I should mention that my built-in volt meter (with the van plugged in to shore power) shows 13.7 volts.

In my installation, as per the diagram, there is a 2/0 red wire going from the left bolt of the ACR to the chassis battery (with a 150A 32V fuse located right next to the ACR). Also, as per the diagram, there is a 2/0 red wire going to the house battery bank in the rear of the van (20 plus feet of wire). I can’t confirm the exact connection in the rear or whether or not there is a fuse back there because the wire goes into the battery box which is a sealed, custom metal box that I can’t open without cutting into some of the woodwork. But my expectation is that there is no problem with this.

However, the black wires are not connected as shown on the diagram. The diagram shows a black wire from the negative terminals of each battery to a common bus bar. Instead, in my installation, the chassis battery negative terminal only has an 8-inch wire bolted to the van frame. On the house battery side, I can’t be certain because I can’t open the battery box, but the black wire coming out of the box goes to the shunt for the Magnum Inverter Control Panel and then it looks like it has a wire a couple of feet long bolted to the frame in the rear.

As for the small control wires: The thin black wire is not connected to a common bus bar, but rather it extends about 8-inches from the ACR and then is screwed to the van sheet metal. The red wire extends upwards to somewhere behind the center of the dashboard. I couldn’t trace it any further so I don’t know where it terminates. The other wires are cleanly cut and left hanging. I suppose the ends could have been protected better, but they don’t appear to be touching each other or anything else. (It wouldn’t be a big deal to cover the ends with electrical tape if you thought that was worthwhile.)

You mentioned that, “It is possible that SportsMobile wired the control wire to the key switch to simulate start assist.” I’m sorry but I don’t know what this means. Maybe you could expand on this.

So, given all this, any other thoughts. Would the differences in the ground wires from what the diagram shows affect the performance of the ACR?

You also said, “If the [red control] wire has a fuse on it try pulling the fuse and see if your ACR will connect ….” I think there may be a small in-line fuse but I’ll have to get back under the van to check. However, I’m not sure how I would tell if the ACR is connecting or not. Is there some kind of indicator?

Another oddity related to the yellow switch on top of the 7622 . It is my understanding that the normal left-facing position is for automatic operation and flipping it to the right disables the device (opens the circuit). However, it is also my understanding that when the switch is in the left-hand position, you should be able to push down the button on the top of the switch to lock the circuit in the closed position, thus connecting the chassis and house batteries. However, when I depress this button, it just snaps right back. It does not lock down. Any thoughts on that.

Again, thank you all so very much. And for taking the time to read my long, wordy (and ignorant) posts.

George

[geo2015]

Fitz, I checked out the discussion you linked on your build pages (posts #617 – 644). Wow, super informative and helpful (Scalf77 has lots of especially insightful comments). It sure makes me think I have almost the same thing happening in my installation. My installation was done in Texas, but I had to push a bit to get them to install the Blue Sea ACR in lieu of the SurePower (I wanted the Blue Sea because of the reduced power draw and concerns about overheating). The fact that the red control wire in my install does not go to a switch but disappears behind the dashboard makes me think that they installed it like a SurePower unit with “Smart Assist” that actually defeats the functionality I am looking for (chassis battery charging from shore power).

To everyone: If it is the case that my Blue Sea was incorrectly wired as if for Smart Assist, could I just cut the red wire behind the dash and use it to add a 2146 remote switch? (Do I need a 12V supply also?)

[Scalf77]

George,
My wire diagrams are pretty generic, So I generally show ground as a BUS-bar, You could substitute the bus-bar as the frame of your van. And it would match your explanation. You have a shunt for the Magnum BMK between the house battery and frame ground. The fusing of the batteries doesn't sound wrong. The black wire again would be "ok", as it is connected to the frame of the van, which is ground so the same as the bus-bar in the picture. I hate when grounds for devices get attached to the frame somewhere,I prefer a centralized location. You need to make sure that the ground for the ACR is tight and making good contact to the frame. When the ACR connects or disconnects it is fairly loud. If you do wire in the switch it has a led indicator.

Are you sure that yellow control knob is all the way to the left? Otherwise it does not sound correct. I admit to so rarely using the knob though.

As far as the start assist wiring, the ACR does not need to have the red control wire hooked to anything for it to operate in automatic mode. So I would be suspect if it is wired to anything other than the approved switch. In general if you provide 12 Volts to the red wire it will connect the ACR; if you provide ground it will disconnect; and if not connected it will be in auto mode.

If your red wire goes to a circuit that is Hot "12 Volts" when running but when it off the wire is ground or a "soft ground" This would not enable the ACR to every go in Automode, but would charge the house when running.

Sorry for the rambling, need another cup of coffee. I will adjust my drawings to not be confusing as to the bus-bar.

-greg