Feathermerchant

tvsjr - I found this a long time ago. Advantages over solenoid.
http://www.hellroaring.com/

tvsjr

Diode isolation also causes voltage drop. I know people who've been happy with the Hellroaring stuff, but I've seen diode isolators fail in weird ways.

The solenoid, especially one that's seriously beefy like the ML-ACR (which is actually a bistable relay with a huge magnet to move the contactor), basically never fails. It also gives you the option (with the ML-ACR, either via the yellow **** on top or via a remote switch) to force the two batteries apart (if something fails) or to force them together (allowing you to jump-start yourself, assuming the battery and the wiring are both capable of handling cranking loads).

stormsearch

Basically everything tvsjr is stating is gtg. I support alot of the local police outfitters, one is using diode isolators with success. But they are mainly used on alot of meter maid type vehicles. What the general consensus is for heavy abusers, the relay isolation is the best option. We are talking vehicles in constant emergency situations, running all kinds of lighting. It is also the only guaranteed way the batteries will seperate when powered off. The dual isolator systems have merits, guess most outfitters stick with something that has been already working. It is pretty common for the outfitter stuff to be connected to the aux battery and there is always seems to be load left on - dvd recorder, cooling fan, etc and would drain both batteries otherwise if not done right.

Overall, don't be overly concerned about the BMS system. The absolute worst that can be caused if disabled or not working right is a DTC to be recorded in the system (no light on dash) and the vehicle operates like it used to before all of this BMS stuff came into existance. This is likely to change someday, actually surprised it hasn't happened yet, due to gov't regulations and EPA (whatever they turn into). BMS disabled could result in draining the main battery while like listening to the radio for hours (the system should default to a standard timer off mode but I haven't checked it) - again just like it could before just a couple generations ago. For a S/S vehicle it would likely be disabled. The load shedding would still be enabled but only for severe operating cases.

If I ever needed to use a secondary battery system often for heavy use, I would just hook them up in parallel directly thru a relay. I would disable BMS to ensure the alternator is putting out voltage based on battery temperature, not state of charge. Unfortunately the temperature would be based off the front main 12v battery but at least would ensure that the system is always in positive charge mode. Isolate the battery while using the aux and reconnect only when the engine is running. Would connect directly from battery to battery with proper fusing. For Hall Sensors, would just bypass it since I've disabled BMS.

For light aux battery use, would use an isolator, keep BMS running and make sure all my wiring was being measured correctly with the Hall Sensor (grounded at body/frame ground or run wiring thru the sensor). Might go as far as setting up a ground distribution block.

Feathermerchant

Thanks for all your help.

Mfitz

I don't want to hijack this thread, but my issue is similar to the OP. You guys are way over my head so I hope somebody can give me a really simple answer. I asked on another thread about wiring a better connection to my travel trailer's 2 6v batteries, to be used for off-grid camping and also supplied by solar panels. My understanding from that other thread was that the stock hot lead in my 7pin trailer connection wasn't going to recharge my batteries very well, so I was planning to run a heavier cable from the truck battery to the trailer batteries, switched by a simple solenoid to prevent me from running down my starting battery. Can I not run the charge system this way? BTW, I have the 2.7 EB with start/stop.

tvsjr

I'd go with a diode isolation system (Hellroaring being the common favorite) in this case. Keep your BMS alive so you don't have any start/stop problems, just make sure the isolator is wired in after the current sensor, so it "sees" the power demand from the isolator. The diode isolation would also prevent power from the solar panels back-feeding the truck. Run that back (through a fuse block or circuit breaker) with proper sized wire (something in the 2/0 range would be my suggestion... keep in mind this cable could see the full force of the alternator and potentially additional current from the starting battery if the camper batteries are deep-discharged) to some sort of disconnect (larger Anderson Powerpoles, like what you commonly find on battery-powered forklifts, would be my go-to).

The 7-pin connector is good for 30A if memory serves... you'll have to decide if that's good enough.

Or, get a 2KW Honda generator and a battery charger and charge them up that way. Probably a simpler and more versatile option.

Feathermerchant

Generator is an idea. I actually sell 12V power supplies that may work to power the emergency equipment you are operating. It is kind of a round about way but gasoline has much more energy stored by volume or weight than any battery.

mjs3350

Wow, if I can get 30A from the trailer plug that changes things for my use. I thought you could only get a trickle from it.

tvsjr

That's what my brain recalls, but do some research and verify. That circuit IS intended as a battery charge circuit for exactly what you're doing. If you're trying to bulk charge a 1000Ah battery bank, it's not gonna fly. But I think what you want to do is entirely possible.

mjs3350

I'll look into it. The plan is for a 150-200Ah house battery that I only plan to drain 50% over a couple days at a time, but there will usually be driving involved during that time.