Looking for help with a weirder build: trailer w house battery, towed by van with house battery. What do?

[ADDvanced]

So here's the basic layout.... the van will have a small house battery to power the 2kw heater (this is the bedroom). The trailer will have a kitchen/work/bathroom and a big battery bank of 2 6v golf cart batteries, and solar panels. The van will not have solar.

So I'm not sure how to manage the smaller house battery for the heater in the van, maybe just a 'dumb' battery switch and click it to 'both' while driving, and leave it off when stationary?

For the trailer... I think a DC to DC charger makes sense, but I would need to run thick cables to the DC to DC charger, correct? So if I mount that on the van... I'd need to run a lot of heavy, expensive cable to get to it, but it needs to be there because that's where the solar controller would be. I see that there are some combination MPPT/DC to DC chargers... but again... how does this work with a house battery in the van as well?

Lastly... is there a way to pull power from the battery bank in the trailer TO the van at night? Maybe eliminate the house battery in the van entirely and rely on the power from the trailer? How would that work?

I have a decent grasp of electrical layout/theory, but my build is sort of strange/weird/different so it's not as straight forward as a single house battery all in one vehicle.

 

[NatersXJ6]

Thinking outside the box a bit… maybe belt drive an alternator off a trailer wheel so it charges while towing?

 

[ADDvanced]

Using an invertor and AC would allow me to use a regular old extension cable, as AC can travel longer distances without power loss, correct? Just making sure I'm picking up what you're laying down.

I think using the trailer to power the van would be awesome.... so I wan that capability, but GF has a requirement of having heat in the van even without the trailer in case we go snowmobiling (sled trailer) we don't want to wake up to a dead battery. So I think I still need a house battery for the heat. Would a simple mechanical battery isolator like this work for the VAN house battery?


Could have #1 hooked up to start battery, and #2 hooked up to a small house battery. When driving, click to "Both" and the alternator should charge both... from what I understand leaving it in both would be an issue as the batteries would fight/flatten each other. Would that work?

 

[john61ct]

DC-DC charger at the second bank would be more efficient if you are using solar

but for just while-driving alt charging, efficiency hardly matters.

Note that a lead bank must get back to true 100% Full as per trailing amps spec, long CV/Absorb stage

most cycles anyway, for longevity

and that takes well over 7 hours, no matter how many amps available in CC/Bulk stage.

 

[mechengrsteve]

View attachment 690072

So here's the basic layout.... the van will have a small house battery to power the 2kw heater (this is the bedroom). The trailer will have a kitchen/work/bathroom and a big battery bank of 2 6v golf cart batteries, and solar panels. The van will not have solar.

So I'm not sure how to manage the smaller house battery for the heater in the van, maybe just a 'dumb' battery switch and click it to 'both' while driving, and leave it off when stationary?

For the trailer... I think a DC to DC charger makes sense, but I would need to run thick cables to the DC to DC charger, correct? So if I mount that on the van... I'd need to run a lot of heavy, expensive cable to get to it, but it needs to be there because that's where the solar controller would be. I see that there are some combination MPPT/DC to DC chargers... but again... how does this work with a house battery in the van as well?

Lastly... is there a way to pull power from the battery bank in the trailer TO the van at night? Maybe eliminate the house battery in the van entirely and rely on the power from the trailer? How would that work?

I have a decent grasp of electrical layout/theory, but my build is sort of strange/weird/different so it's not as straight forward as a single house battery all in one vehicle.

Remember, that deep cycle batteries have higher internal resistance than starting batteries, even though are both lead acid and just by nature of having two different batteries in the system, you will not get good charging to either of your house batteries. In a perfect world where $ grows on trees, using a B2B charger for each separate battery bank would be best and never conencting the two battery banks would be best. Because they are greatly different in capacity, they are unlikely to be at similar SOC or operating voltage so will not be easy to reconnect if separated and will not behave well together even when they are connected.

I believe here is a better concept. I assume the priorities are 1) there is a preference for your 'camper(s)' to operate as if there were one power system, 2) there is more weight capacity for batteries in the 'trailer' than the 'van', 3) there is no need for the two units to operate separately. If these are true, I would 1) make a single battery system in the 'trailer' with all identical batteries, 2) run a bus cable from behind he driver seat in the van to the battery in the trailer to privide a power distribution bus for a single house battery system. 3) Place an appropriately sized Anderson coupler near the hitch because there will be times where disconneceting is needed. Disable the B2B if you drive without the trailer. 4) place a B2B charger in the van, behind the driver seat, connected to the front end of the bus cable. All house power comes off the bus cable with separate fuse panels in each body.

 

[VanWaLife]

Kind of off topic, but shouldn't the one in back be a Ford?

 

[4000lbsOfGoat]

Any chance you could use propane heat to eliminate the need for battery systems capable of running a heater all night? It would greatly simplify your electrical needs.

 

[john61ct]

Yes, heating from battery stored energy directly is not smart.

I assumed electricity was only used for the control systems & fans

of a parking heater burning the TV propulsion fuel, or as you say propane.

 

[mechengrsteve]

Any chance you could use propane heat to eliminate the need for battery systems capable of running a heater all night? It would greatly simplify your electrical needs.

The idea may seem good but unvented propane combustion creates several hazards. Combustion of 1lb of propane results in the creation of 1.6 lbs of water which is a significant hazard in wetting interior contents, condensation everywhere, etc. There also is the potential for incomplete combustion due to oxygen starvation which creates carbon monoxide. most modern propane devices have Oxygen Depletion Sensors which shut down if low oxygen content is detected but the downside of the CO threat is pretty steep (death) and in such a small space, things that go bad, get serious quickly. I personally think unvented propane combustion in any enclosed space is a bad idea.

 

[john61ct]

Parking heaters are by definition vented, in fact many are located outside the living space completely.

Webasto, Espar dominate the propulsion fuel side

Propex HS2211 is a good propane example.

I agree those that burn into the living space are more complex, less safe and less efficient once you take care of their issues.

 

[mechengrsteve]

Glad you agree. I have seen SO MANY garbage RV blogs that encourage people to 'get a portable propane heater, you'll love it' and many people will just suck up that BS without understanding what they are getting into. In particular, using propane as a fuel consumes a huge amount of space (if stored internally). I measured my 2-30lb cylinders on my old Lance truck camper as consuming 6cuft and weighing 120 + lbs (tanks, compartment and fuel all in the camper space) versus my 14-gallon aux diesel tank that weighs ~90 lbs in 3 cuft under the truck cab, carrying a similar amount of energy and providing vehicle fuel backup (which I use often).

I have both a diesel air heater and diesel coolant heater and I love them. I think your idea for a 'propulsion fuel' heater is the right one but it does take ~8A to start (for ~ 2 min) and 2A to run which is not insignificant if on overnight. I kind of wonder how you'll find them working in your small space with relatively poor insulation (mostly because of lots of single pane glass). Condensation will be a big thing for you and would be a huge issue if you were to use a portable propane. My camper is (inside) 7.5' wide, 7' high and 12' long with a 7'x7'x3'h bunk. I have 2.5" thick walls with 2" of polyiso insulation and 7 double pane windows. The 5kw diesel air heater running on its lowest speed will keep the whole camper warm in 30-degree weather. On much higher speeds, it will cook you out quickly (or warm up a cold camper quickly). Its not ideal to continuously operate at low speed, as soot accumulates. I have heard but not myself investigated that the only difference in the 2kw and 5kw units is the programming for max fuel pump speed. I wonder if this is the same as running the 5kw on the lower 40% of fuel pump speed? I do make sure to ramp up my heaters occasionally (works well to do it at shower time).

Also speaking of 'heating from battery power'....Its always a terrible idea to use a high-quality energy source to provide heat. The one exception may be, to use it to operate a heat pump. I have a big battery and have, on occasion, used my 9kBTU LG heat pump to warm up the camper in the morning (when I transferred all my heating diesel to the truck tank)....still a bad idea but about 4x more energy efficient. As long as I get 'power to burn' from my solar panels, it is not a problem.

 

[mechengrsteve]

Using an invertor and AC would allow me to use a regular old extension cable, as AC can travel longer distances without power loss, correct? Just making sure I'm picking up what you're laying down.

I think using the trailer to power the van would be awesome.... so I wan that capability, but GF has a requirement of having heat in the van even without the trailer in case we go snowmobiling (sled trailer) we don't want to wake up to a dead battery. So I think I still need a house battery for the heat. Would a simple mechanical battery isolator like this work for the VAN house battery?

View attachment 690105
Could have #1 hooked up to start battery, and #2 hooked up to a small house battery. When driving, click to "Both" and the alternator should charge both... from what I understand leaving it in both would be an issue as the batteries would fight/flatten each other. Would that work?

Not a good idea to join battery banks that are not at the same SOC. What you describe is how these switches are intended to be used BUT and there is always a BUT, the more charged battery will immediately begin charging the less charged, even if are not using any electricity. If the charge difference is great, the current could be large. SInce lead acid is only about 90% efficient in charging (9 parts go into the battery, 1 part becomes heat), then its not 'free' to charge one battery with another.

 

[john61ct]

When a powerful enough charge source is active, joining two not-huge banks at disparate SoC is no problem

current flows from the highest voltage source to both banks

not from the fuller bank to the emptier one.

An automatic combiner / VSR /ACR switch is infinitely better than a manual one.

Lead is self-limiting anyway, but if LFP yes could dangerously fast heat up your wiring infrastructure.

DCDC / B2B chargers between banks is better, but yes charging bank to bank from stored power rather than a real charge source is very very wasteful

 

[ADDvanced]

Thanks for the input guys. Still not sure what I'm doing yet. Maybe I'll just put the heater and a few other things on a switch in the actual van, so it could draw power from either the house battery, or the trailer battery.