Lipo charging setup for the bed of my truck

[Bingoman]

I run a diesel heater for my camp, and power it off a 100ah lipo battery. I would like to back the battery power up from my alternator, while the heater warms up(this is the most power consumption, like 100w) then when the glow pug is going, turn the truck off and use the battery only.
I'd like a streamlined setup, that I can disconnect when I'm not camping, but not afraid to have some permanent hookups in my truck bed somewhere discreet.
Can anyone with experience with these setups help me dream up a system to do it with? I have a 20a DC to DC charger that I think I can use for the charging, but may not be enough.
Thanks in advance

 

[Bingoman]

Is that typo ?
100 mAh might get you couple min. runtime.

It sure is a typo, thanks

 

[Dave in AZ]

Seems unnecessary. Initial startup is just 110w for like 3 or 4 minutes. So total of like 7 Watt-hrs to start. Then it runs at 12 W to 45W at highest.

If you already have a dc dc, and want a backup, juat hook it up to your other battery. I assume by lipo you actually mean LiFePO4 12v? Lithium iron phosphate?

Anyways, that is plenty of boost, 20A at 13v or so is 260W.

 

[Bingoman]

If you already have a dc dc, and want a backup, juat hook it up to your other battery.

One thing I'd like to achieve from the install, is to charge the battery as I'm driving, but not when the vehicle is off. Would that be achievable from the battery, or better from the alternator?

You are correct, it's a lifepo4 12v battery

 

[burleyman]

Does your truck have a 7 pin connector? I run a 12v fridge and charge a 30ah lifepo4 in the back of my truck while traveling via a 7 pin female connector with only two wires attached to the male connector. The wires go through a gap in the tailgate while closed.

The vehicles I'm familiar with have a 30 amp fuse at the front that feeds that 12v to the rear. There are many camper trailers with batteries being charged while driven with little thought given.

If the 12v at the connector is not turned off and on (switched), you will have to remember to unplug when parked to avoid draining the starter battery, or having the bed battery being drained by the starter battery. I don't start the truck with the batteries connected together.

Your 100 amp hour battery will run that diesel heater for quite a while. After turning off the glow plug, the fan and pump draw about one amp.

 

[SlowCarFast]

One thing I'd like to achieve from the install, is to charge the battery as I'm driving, but not when the vehicle is off. Would that be achievable from the battery, or better from the alternator?

You are correct, it's a lifepo4 12v battery

If you utilize a DC to DC charger, your house battery (the one powering your heater) will not charge from your starter battery when the alternator is not running. The charger identifies when a charging voltage is present (alternator running) and only charges in that case. There would be no concern of a drawdown of your primary battery. There is no difference electrically between wiring your charger to the starter battery terminals vs directly to an alternator (you should connect to your battery terminals, it's more practical). Your current house battery should be capable of providing the required amperage draw at heater startup, so there is no need for it to be connected to the alternator at the specific point in time. You could utilize an Anderson connector, or other quick disconnect between your DC to DC charger and your house battery so that it's easily removable from the truck, and just keep things organized such that you can plug in the battery when you're on the move. You'll want to do some research regarding proper wire gauge and fuses at points throughout your system. Undersizing wire for your expected power draw, or not correctly fusing for your wire size creates a very real fire risk. It is not complicated, and certainly a very feasible DIY, but not something you want to mess up!

 

[Dave in AZ]

@SlowCarFast said what I would have
What you ask for is the exact reason dc to dc alternator chargers exist-- charge a 2nd battery while car runs, without letting starter battery get drawn down.

 

[Dave in AZ]

@burleyman , I'm interested in this using 7 pin tow connector. My understanding is that power there is very minimal, and is just supplied for trailer running lights or brake controller. I have recently added a 3rd brake light to my camper from this 7pin, and the wires there are quite small, they don't even look like 14 AWG to me, more like 16 ga. Which is like 5A max on a 50ft round trip run from battery, which the trailer hitch pretty much is. Even 14awg only has 30ft for 10A, to stay above 10% voltage drop, and for sure those wires are not 12awg on my Tacoma.

Do you have any info on max power limits thru those wires, or where I might find that? Nothing in my Tacoma manual indicates using that to power stuff really, just talks about lights and turn signals, that I can find?

 

[Pacific Northwest yetti]

X2 with SlowCar Fast,


Without doing the math, you will need 4ga or even 6ga would probably do that. I have 4ga from my truck, to a Victron DC/DC, through Anderson plugs and into the Lithium bat bank for my Outfitter. W/ 50amp ( I think its 50) breakers. For what its worth my brother has a business that does this. Zero Declination in Reno. I trusted his judgement when I asked him about mine.


The tiny 7 pin connectors are not designed to provide much power.

 

[Pacific Northwest yetti]

Edit,
A good write up here:

Four Wheel Camper Electrical Basics and Switching to Lithium!

FWC Lithium Manifesto Ok, lately especially, my inbox has exploded with questions about DIY installation of lithium batteries into Four Wheel Campers. We’re talking 5 new inquiries a day. There is a lot of info about it on here already, but I thought maybe it would be helpful if I put it all...

forum.expeditionportal.com

 

[Bingoman]

Thanks for all the great info. I plan to use #8 strand from the battery to the dcdc charger (it's a 20a), about 15'
Per the manual I found online:
30a breaker before the charger
25a breaker after the charger
#10 wiring from the charger to the house battery (about 8')

 

[SlowCarFast]

One note about your fuse or breaker (I used fuses). The intent of the device is to protect the wiring (and your downstream electronics) from overheating or fire in the case of a device overdraw or a short circuit. With that in mind, you'll want your fuse as close to the power source of each cable run as practical to maximize protection.

I didn't check your numbers, but generally your approach looks about right! It should be noted, I have zero qualifications in this sorta thing, but I did install a house battery system in the car and haven't burnt it to the ground yet 😄

 

[Buddha.]

@burleyman , I'm interested in this using 7 pin tow connector. My understanding is that power there is very minimal, and is just supplied for trailer running lights or brake controller. I have recently added a 3rd brake light to my camper from this 7pin, and the wires there are quite small, they don't even look like 14 AWG to me, more like 16 ga. Which is like 5A max on a 50ft round trip run from battery, which the trailer hitch pretty much is. Even 14awg only has 30ft for 10A, to stay above 10% voltage drop, and for sure those wires are not 12awg on my Tacoma.

Do you have any info on max power limits thru those wires, or where I might find that? Nothing in my Tacoma manual indicates using that to power stuff really, just talks about lights and turn signals, that I can find?

If you’ve got a factory seven way trailer plug you should have a power wire in there that is separate from lights and brakes. It’s usually ten gauge and fused at 20 or 30 amps.

 

[Bingoman]

One note about your fuse or breaker (I used fuses). The intent of the device is to protect the wiring (and your downstream electronics) from overheating or fire in the case of a device overdraw or a short circuit. With that in mind, you'll want your fuse as close to the power source of each cable run as practical to maximize protection.

I didn't check your numbers, but generally your approach looks about right! It should be noted, I have zero qualifications in this sorta thing, but I did install a house battery system in the car and haven't burnt it to the ground yet

Cool, I think I'll move the wire size up to #6 to CMA . I found some marine grade breakers that should work at the boat store. They can surface mount.
To your point about mounting the breakers close to the power source, that would mean between the charging battery and the DC charger the first one would want to be closest to the charging battery. Then for the protection in between the charger and the house battery, would the protection want to be closer to the charger, or the house battery?

Also, I've heard this charger (renogy) may not work right if I just run the negative to the chassis. I should plan on two runs all the way back to the starter battery correct?
I think it needs a control wire from the ignition, which I didn't plan for originally.

 

[highwest]

@burleyman , I'm interested in this using 7 pin tow connector. My understanding is that power there is very minimal, and is just supplied for trailer running lights or brake controller. I have recently added a 3rd brake light to my camper from this 7pin, and the wires there are quite small, they don't even look like 14 AWG to me, more like 16 ga. Which is like 5A max on a 50ft round trip run from battery, which the trailer hitch pretty much is. Even 14awg only has 30ft for 10A, to stay above 10% voltage drop, and for sure those wires are not 12awg on my Tacoma.

Do you have any info on max power limits thru those wires, or where I might find that? Nothing in my Tacoma manual indicates using that to power stuff really, just talks about lights and turn signals, that I can find?

My Tacoma (w/ tow package) puts out less than 5A to my trailer through the 7 pin connector. When I added a 30A DCDC charger and house battery to the truck bed, I ran 2AWG wires from the starting battery.