Automatic charge controller or battery isolator voltage measurement

[Rosbif06]

I have a FWC fleet with a 1314A battery isolator which I'm looking to change out with a Blue Sea ACR to increase efficiency.

I've been thinking about the operation of any ACR or battery isolator, and perhaps there is an important gap in my understanding of how they measure the voltages of the vehicle and house batteries, can someone please clarify/confirm?

If the engine is running and ACR/isolator is connected and the batteries (house and vehicle) are charging, all is good. When the vehicle is switched off, the voltage at the ACR/isolator will drop and the house and vehicle batteries will be disconnected.

However, if there is a solar charger on the house side, then the voltage as measured at the ACR/isolator will remain high, and the batteries will remain connected until the solar charger also drops its voltage?

My assumption is that when connected, the ACR/isolator cannot differentiate between house and vehicle battery voltages until they are disconnected? Is this correct or is there some clever way they can that I don't understand?

Thanks for the education!

 

[rando]

Your understanding is spot on - when the two batteries are connected starter voltage = camper voltage, so they stay connected until the voltage drops below 12.75V. If you have solar connected to the camper battery, the two will stay connected until the solar charger drops.

I consider this a desirable feature as it keeps both the camper and truck batteries full charged when they are sitting in my driveway. Even after sitting for a couple of months, the truck always roars to life.

If you install the SI-ACR model isolator (or the ML-ACR which is overkill for this application), you can add an override switch, which forces the ACR to isolate the batteries. Alternatively you can just switch the ground lead on the regular ACR, but I am not convinced this is good practice.

 

[nevadamerica]

I have the SI-ACR. Bluesea 7610. I used i think 0 AWG to link the two batteries, and a 175A in line fuse, as my trucks alternator is rated around there.
I LOVE this addition, it has been everything I hoped for.
I do not have the start isolation installed. Maybe this is killing my camper battery, but I think it's fine, and I maintain it otherwise.
Lead acid on both sides, and I just looked last night if you can have mixed chemistry between the two batteries, (ie lithium in the camper) but I'm not sure that you can.
Been going strong for a few years now, no issues. I put a huge quick connector where the camper meets the truck, and can be seen in the link... https://www.amazon.com/Anderson-SB175-Style-Connector-Power/dp/B00RU4LCGU

 

[Vic Harder]

0 AWG... wow. I am using 4 g and see 40-80A regularly, so the alternator is charging the house batteries nicely. And when parked, like rando says, the 265W solar panel is charging both as well.

Question for the OP, what is your concern about the two batteries being connected when solar is active?

 

[nevadamerica]

0 AWG... wow. I am using 4 g and see 40-80A regularly, so the alternator is charging the house batteries nicely. And when parked, like rando says, the 265W solar panel is charging both as well.

Question for the OP, what is your concern about the two batteries being connected when solar is active?

I thought it was a bit much too, but it was recommended by the instructions and a blue sea representative as well. It’s not crazy expensive, and pretty common in car audio installation.

Again it was based off max possible alternator output, which hopefully it doesn’t reach.

 

[crashmaster]

Alternatively you can just switch the ground lead on the regular ACR, but I am not convinced this is good practice.

I was thinking of simply pulling the fuse from the ACR ground on low sun angle or overcast days when I would need all PV going to the house battery. I would prefer that to installing a ML-ACR but seeing that might not be a good practice, what potential problems exist? Could it damage the ACR or something worse?

Thanks.

 

[rando]

I am not sure pulling the ground will cause any issues. In general electrical terms, "loss of ground" can be a problem, particularly with large coils (such as relays) as they need somewhere to dump the power spike generated from field collapse when the relay is de-energized which could damage the ACR.

This is all just "good practice" and 9/10 even when not following "good practice" everything works out just fine.

It may be easiest just to install a manual override circuit breaker (if you don't already have one) to isolate the starter batter.
However if you do want to be able to override the ACR, you can install the SI-ACR, which is about 1/2 the cost of the ML-ACR.

 

[crashmaster]

Thank you rando, that makes prefect sense.

 

[Wildcat]

I installed bluesea acr 7622 with the remote switch which has worked out better than I anticipated. When I bought it I didn't really know if I was going to use the remote, but I subsequent upgraded the camper battery to lithium and then realized the acr was still linking the truck and camper batteries when the ignition was off because the lithium is almost always at a higher voltage than the truck starting battery (optima). So I've gotten use to using the remote switch in the cab to turn on (link) the batteries when I'm driving (if needed) and unlinking the batteries when I'm parked (but sometimes I forget to delink when parked). I have a victron monitor in the cab to watch the lithium battery status while driving. And I don't have a solar setup so the only charging of the lithium is from the truck generator (unless I'm home, in which case I'll top off the lithium with a wall charger). Someday when the optima starting battery dies I will see if it makes sense to replace it with a lithium, in which case the acr can probably stay on the automatic setting instead of me using the remote switch to control the linking. (Side note: a newer lithium in the truck with the older lithium in the camper may still not be the best combination for the acr automatic linking but I'll cross that bridge when I get to it). I'm just a do-it-yourselfer and perhaps my logic and setup are not quite correct, but it's been working for me for the past 3 years.

 

[ntsqd]

Several years ago BEP Marine offered both "Single Sense" and "Dual Sense" versions of the VSR. As you might guess the former could only sense a charging condition on one of it's battery terminals while the latter could sense a charging condition at both of it's battery terminals. Prior to that they only offered a single sense version.

I expect that the Dual Sense logic goes something like:
Contactor Open, monitor each battery terminal independently for voltage above threshold.
If voltage above threshold detected on either terminal: close contactor
When voltage drops below disconnect threshold: Disconnect and resume independent monitoring.

There should be some sort of fuse or breaker at the starter battery anyways. I use a 285 series Blue Sea breaker at both ends. Which allows me to disconnect both battery banks from the wiring between them for whatever reason. If that's not what you're currently using it shouldn't be too big of a project to replace the existing with one or two of them.

Rando, when you said "switch the ground lead on the regular ACR" were you thinking to install a SPST switch in the ground reference wire of a simple ACR? If so, I've pondered that too. I guess I should talk to the guy at work who heads up all of our contactor testing about the downsides of doing this.

 

[pvstoy]

I went with the Blue Seas ACR with remote switching. For me I leave the switch in the off position. I want the camper batteries to be in a closed state and allow the solar to charge the camper batteries. With the Victron battery monitor I can monitor just the camper batteries and not be influenced by having the truck battery involved. I get a accurate reading and monitor health of the camper battery keeping them separated.

I have yet to camp in the winter to see if the 480 watts can keep up with demand. I have the option to use the alternator to charge and solar to charge the truck battery. But for now the solar is doing just fine for the camper.

 

[crashmaster]

I will put a Blue Sea breaker on the starting battery. The breaker FWC has on there is a cheap 30A automatic breaker and I want a switchable breaker anyway.

After reviewing the ACR's. I am starting to feel dumber than normal. I dont quite understand the difference between the BatteryLink and the SI-ACR. I see where the ML-ACR has a switch on the relay itself, and also a remote switch. The only difference I see between the BatteryLink and the SI-ACR is that in the instructions for the SI-ACR it shows and optional switch in the ground wire. So am I correct to understand that it is ok to do that with the SI-ACR but not with the BatteryLink? Could I just use any SPST switch for the ground of the SI-ACR?

After seeing those instructions I am inclined do that with the BatteryLink I already have, and if it gets damaged because of that, I will get the SI-ACR. I'm sure there is something about it I dont understand.