Blue Sea 7622 relay with AGM truck and LiFepo4 camper battery

[TahoeT]

I am removing the FWC isolator and replacing it with the Blue Sea 7622 ML-ACR. I will have two Blue Sea 187 circuit breakers, one at the truck battery and one at the camper battery area. My truck battery is AGM, my camper battery will be LiFepo4. My system will is set up to charge both my truck and camper batteries and prevent a truck battery drain. When I spoke to a friend who owns a Alternator shop, he was concerned about the system since I will have two different type of batteries. Is there a danger in destroying either battery. I do not believe my RV mechanic will be attaching anything to my truck alternator. Thanks for your help. Tim

 

[rando]

There is no danger of destroying either battery. However, you will quickly find that the ACR rarely disconnects. The resting voltage of the LiFePO4 battery is ~13.2V, which is above the disconnect point of the ACR.

Why do you want the ML-ACR, and why are you replacing the FWC ACR? Depending on your usage you may do better with either a simple relay, or possibly a DC-DC charger. If you have a newer camper with the Bluesea ACR, then there is no real need to replace it.

 

[pvstoy]

Rando he has a older FWC with the older style Surepower battery separator. I believe it is on a new Ford Truck so the alternator should put out at a higher voltage.

Good point about the resting voltage of LiFePO4 battery. I believe Tim is looking at the ACR with the manual switch and that should allow a means of disconnect when the truck alternator is not needed. His solar plan of 160 watt with a Victron MPPT smart charge controller should do most of the work?

I'm not knowing on the LiFePO4 battery setup to have any help in the design.

 

[rando]

The older Surepower may actually be an advantage here, as my understanding is that it is only single sensing - it only activates when the truck battery voltage > 13.2V and does not watch the camper battery, meaning it won't be as easily tricked to stay on because of the resting voltage of the lithium battery.

The ML-ACR will certainly work well in this application, but it may be a little overkill - no need for a 500A rating and the lockout function can be provided using the circuit breakers.

I think TahoeT is planning a DIY LiFePO4 system (maybe that has changed?), so I think the best way forward would be to figure the battery out first and come up with a complete system diagram (Battery Cells, BMS, Solar, ACR or DC-DC) before buying any components piecemeal.

 

[TahoeT]

I have been on CHAT with two China companies the past two nights. Communication with them is difficult to say the least. However, the Country is in chaos with many workers at the Lithium/power companies are not coming to work and their battery orders are falling behind. As I speak, I have decided on a 4-pack 280 ah build. Hopefully I can get it and God only knows how long it will take to get here. The Overland 160 is on its way. Working on the frame now. I haven't installed the Blue Sea 7622 yet, so I can return it if I made a bad choice. Headed to my RV shop on Wednesday and he will install my Isotherm 85 and wire my truck...so I have a couple of days to get it right. Thanks for all your input an suggestions. Tim

 

[Vic Harder]

+1 on what rando said. You may also find you never need the alternator to charge your camper battery. And I would be a little concerned about hooking up your alternator and letting it "see" a fully discharged 280AH battery, as it will try really hard to charge those fully in a short time. That might stress your alternator.

Plus, with 280AH, you will likely be able to go several days without charging. What loads are you putting on it? Your 160W panel may be able to keep up with your daily AH draw.

 

[PaulT]

The older Surepower may actually be an advantage here, as my understanding is that it is only single sensing - it only activates when the truck battery voltage > 13.2V and does not watch the camper battery, meaning it won't be as easily tricked to stay on because of the resting voltage of the lithium battery.

I still have the older Surepower in my 2014 Hawk with Battleborn LiFePO4 in the camper and a yellowtop Optima AGM in the 2010 Tundra. I found that while the Surepower did not engage to power the truck battery, neither did it disconnect after running the truck. I had a constant draw on the LiFePO4 batteries of 2+ amps with the truck off. I assume that .9 amps were keeping the Surepower relay engaged with the remainder keeping the truck battery charged.
After disconnecting the power at the FWC installed 30 amp relay under the hood, the current draw from the camper battery ceased. I found that putting the NOCO charger back on the truck battery to ensure it reached full charge once a month or so was again a good idea. Depending on how much driving I did, the NOCO LEDs would indicate that the truck alternator/regulator was keeping the truck battery somewhere above half full but rarely above 3/4 full. As usual, YMMV.

I had bought one of the 7622 units for use on a boat project and had planned to install it in the camper/truck but higher priority projects interfered. It is hard to get to the Surepower in the camper without destroying my back in the process. I know. Excuses, excuses.

Paul

 

[rando]

I still have the older Surepower in my 2014 Hawk with Battleborn LiFePO4 in the camper and a yellowtop Optima AGM in the 2010 Tundra. I found that while the Surepower did not engage to power the truck battery, neither did it disconnect after running the truck. I had a constant draw on the LiFePO4 batteries of 2+ amps with the truck off. I assume that .9 amps were keeping the Surepower relay engaged with the remainder keeping the truck battery charged.
After disconnecting the power at the FWC installed 30 amp relay under the hood, the current draw from the camper battery ceased. I found that putting the NOCO charger back on the truck battery to ensure it reached full charge once a month or so was again a good idea. Depending on how much driving I did, the NOCO LEDs would indicate that the truck alternator/regulator was keeping the truck battery somewhere above half full but rarely above 3/4 full. As usual, YMMV.

I had bought one of the 7622 units for use on a boat project and had planned to install it in the camper/truck but higher priority projects interfered. It is hard to get to the Surepower in the camper without destroying my back in the process. I know. Excuses, excuses.

Paul

This could be a good argument for the ML-ACR unit - at least when it is on all the time it is not drawing as much power.

If you already have the ML-ACR, then there is no reason not to use it as the only draw back is cost. I would certainly lock down the battery specs/design before going any further.

As Vic points out, you may not want to install an ML-ACR and fat wires from the alternator to a 280 Ah battery pack as this could be hard on your alternator. Thinner wires may be useful to limit the current to the battery, but a carefully chosen BMS could also help with this.

 

[TahoeT]

I bought two 60 amp circuit breakers with the thought of using 6 gauge wire. If you think i should use maybe 8 or 10 gauge, I can make that happen. My appointment with Ed's RV (quality shop) is on Wednesday. thx Tim

 

[ntsqd]

If you location will support it I would seriously consider solar over alternator charging. It is nice to have both, but the single 100W solar panel on our old camper stayed ahead of it's needs 80+% of the time so long as I kept the panel clean. Same is true of the 160W panel on our newer, much more electrically demanding Hallmark.

I wonder if putting a resistor in the ACR's ground reference wire would "pull" the disconnect voltage down, or would it "push" it up?