House battery as helper to Truck battery

[Lighthawk]

Friday evening, 5pm: The camper was packed. The dog was on her rear seat platform and my sweetie was seated beside me. I turn the key in the ignition. Nada. Zip. Zero. Dead battery.

My fault, really; I left the dome light on. But, wait! Isn't the solenoid smart enough to flow juice both ways? I had read that in the manual (apologies, I don't have model info with me), that the smart solenoid would assist the truck battery. That thought has given me some peace of mind when we've been in remote locations.

Apparently, there must be a minimum of three volts from the truck battery or it will not work. Worse yet, I'm fairly sure my jumper cables would not reach between the two batteries. And pulling the house battery is a project, even with a screw gun.

I thought I would pass this along, since it was a bit of an eye opener for us. Oh, and we jumped the truck and still made it to our camp spot by sunset. : )

 

[Stalking Light]

I put a small solar controller and SAE plug on my truck battery so I can use my foldable solar panel to charge it albeit not jump start it.

 

[Bosque Bill]

The battery separator the FWC uses (model 1314A) is unidirectional preventing the house battery current flowing to the truck battery if the house battery is at a higher voltage. You can "jump" the two terminals on the side of the separator to connect the house battery to the truck to start it (but I've never tried this, so proceed with caution as the wires are not very thick, i.e., if the truck doesn't start right away, stop before you melt the wires. I would only try this in the most extreme circumstance, or emergency.)

 

[rando]

On my previous builds, I have always taken the time to choose an isolator/solenoid that can handle starting current, run heavy gauge wires between the house batteries and starting battery, and have an over-ride switch on the isolator to force the batteries together. However, this time around I just bought one of these:

https://www.amazon.com/gp/product/B015KFGV52/ref=oh_aui_detailpage_o09_s00?ie=UTF8&psc=1

Starts my Tacoma with no problem! It has the advantage of being fully independent from the vehicle/camper electrical, I can jump anyone else I may run into, and charge my iphone in an emergency. It is also way cheaper than 25' of 2AWG cable.

 

[craig333]

If I ran an isolator (I don't) I'd wire in a switch to do just what Bill said, but instead of starting it immediately let it sit a while and charge the truck battery.

 

[Lighthawk]

On my previous builds, I have always taken the time to choose an isolator/solenoid that can handle starting current, run heavy gauge wires between the house batteries and starting battery, and have an over-ride switch on the isolator to force the batteries together. However, this time around I just bought one of these:

https://www.amazon.com/gp/product/B015KFGV52/ref=oh_aui_detailpage_o09_s00?ie=UTF8&psc=1

Starts my Tacoma with no problem! It has the advantage of being fully independent from the vehicle/camper electrical, I can jump anyone else I may run into, and charge my iphone in an emergency. It is also way cheaper than 25' of 2AWG cable.

Interesting item, but at 1.4 lbs. it's only for the truck, not my backpack.
I initially thought your device would jumper the isolator, which would replace my jumper cables. Well, maybe not peak cranking load, but for charging up the truck from the camper.

Which leads to that idea: Why not jumper the isolator when you've got a dead truck battery (and a hot house battery topped off with
Disclaimer: I'm not an expert in electrical, and barely manage a multimeter.

 

[DrJ]

Lighthawk,

This is one of the reasons why I changed out my battery isolater. I changed it for the bluesea ACR and then added a switch to the system.

Now I can jump the truck batteries from the camper or even charge them with the camper solar system.

I have a diesel and they require a lot of power to warm the glow plugs and start the engine. I don't like being stranded so I really like the back up safety feature this added.

Here's the link:

http://www.wanderthewest.com/forum/topic/11861-automatic-charge-relay-how-to-improve-your-battery-isolator/?fromsearch=1

I have used that jumper before. It's ok but struggles with a larger battery and starter system.

 

[ntsqd]

I would say that if your back-up plan is to jump from the camper battery with it still in the camper that both the power and the ground wires between the batteries need to be at least 6 gauge with 4 gauge being much better. Sometimes all that's needed is to keep the voltage up while cranking. Smaller wires can work for this. Other times you'll need to draw large amps and smaller wires will not work for this.

A 25+ year Repair Tech friend of mine carries one of those LiON jumper batteries in his back pocket as part of his normal routine at work. This is the one that he recommended to me: https://www.amazon.com/dp/B00MQ5Z5F2/ref=wl_it_dp_o_pC_nS_ttl?_encoding=UTF8&colid=39ZOO8M7P7W1T&coliid=I2GXBYQGLWYAF8&psc=1

 

[Happyjax]

I would be very cautious about trying to start a vehicle with true deep cycle batteries as they are not rated very high in CCA. The solar panel charging of the truck battery may take a day but is safe and should work as long as the battery cells are all okay I also have one of the portable jumping systems and used it once. Worked well

 

[rando]

You certainly could just jumper around the isolator with a 6" cable made just for this purpose - or even more simply, just move the two wires on the isolator to the same terminal. The drawback to this is that everything in the chain between your camper battery and starting battery needs to be burly enough to handle the craning current - which can easily be over 100A. As someone else mentioned, this means 6 or preferably 4AWG wire, 100A+ circuit breakers/fuses at both ends of that wire etc. This gets to be both heavy and expensive. I feel that the jump pack is a better option both in terms of $$$, weight and redundancy.

Just to add, I am currently installing the truck side wiring for my new Fleet Flatbed that is arriving next month - and I did end up going with 6 AWG cable and a blue sea ACR because that is what I already had on the shelf. In my case I am using a lithium battery in the camper, which I have purposely limited to a max of 30A charge/discharge rate, so I can't use it to jump the truck. However, if I were to run the truck batteries down out in the boonies, I can still use the solar system in the camper to charge the truck batteries, although it could take a full day to recharge the battery. Having the solar and the jump pack seems like a belt and suspenders type approach.

Interesting item, but at 1.4 lbs. it's only for the truck, not my backpack.
I initially thought your device would jumper the isolator, which would replace my jumper cables. Well, maybe not peak cranking load, but for charging up the truck from the camper.

Which leads to that idea: Why not jumper the isolator when you've got a dead truck battery (and a hot house battery topped off with
Disclaimer: I'm not an expert in electrical, and barely manage a multimeter.

 

[wuck]

The 1314a is normally unidirectional, however you can add a low current switch in order to close the contacts for bidirectional use. I would recommend adding an indicator light also to prevent two dead batteries, as the contact closure uses about 3/4 amp. As mentioned already, with the long small gauge interconnect wire use this mode primarily to charge the truck battery. Any cranking would have to be done very quickly to prevent damage to the wire.

Surepower 1314a install manual

View attachment Sure_Power_ 1314A_Battery_Separator.pdf

And, if anyone hasn't heard about it:

Surepower 1314/1315 recall notice.