Instead of Connecting House and Startup Battery via Solenoid Can I use a 1.5 amp mai

[BenDwel]

So I am about 90% complete with my Ford Transit Connect Conversion. Hopefully I will put a complete writeup on here about it soon.

I had a quick question about charging the house battery via the startup battery. It seems like the most popular solution is to do the solenoid route. However I don't want to have to manually wire the two batteries together plus I think that my solar panel setup will likely be more than enough to keep my batteries charged.

Thus I figured that a less efficent (but easier route) would be to use an inverter connected to the cigarette 12 volt source and then from that have a 1.5 amp battery charger/ maintainer connected to it. I would set the connection to a fuse that would only be on during run. Two questions.

1) This should work right? It seems the biggest concern would be the amps and the wire guage but if using a 1.5 amp maintainer that shouldn't be an issue.

2) I was thinking that it would be if I could get the inverter out of the solution entirely and just use a 12 volt powered maintainer. However anytime I try and search for a 12 volt powered battery maintainer it gives me an AC powered maintainer that can charge 12 volt batteries. Does anyone know if a 12 powered battery maintainer exists? I am doubtful it does.

 

[SternWake]

If you have solar, dont bother with maintainer unless you park in garage.

 

[Reducto]

A maintainer will do little to keep up with any real usage of the house battery, especially if it's only on when you are driving. Better to just give things a shot with the solar by itself and see if that's enough.

 

[ccbreder]

The outlet is 12 volts +/-. your house is 12 volts +/-. What does the inverter charger do?

 

[Trebor English]

The key to making the starter battery / house battery / solenoid plan work is to have a low resistance connection.  With a substantial resistance the voltage drop limits the current flow to levels that are ineffective.  With a short vehicle like a Transit Connect a short fat wire should be possible.

If you wanted to charge a battery in a trailer the inverter charger plan has some merit.  The long transmission line from the engine compartment to the trailer is 120 volt reducing the losses.  The resistance loss in the cable is a tenth and the charger can adjust over the range of 110 to 120 volts to give consistent charging.  Higher charge currents are more important with AGM batteries.  If you want to maintain 14.8 volts for two hours to a battery in a trailer the inverter / charger plan could work.

A 1.5 Amp maintainer would not do much for charging a house battery.  A 12 or 14 gauge wire from a cigarette lighter socket plug to the house battery would do more charging but still not enough to make up for a substantial use of the battery.

 

[SternWake]

When batteries are depleted below 75% they can accept large currents.

Agm batteries basically like higher charge currents.

An inverter plugged into stock ciggy receptacle can only pull about 120 watts maximum. And only for short periods. Generally without upgrading plug, receptacles. And wiring, anything more than 60 watts is a bad idea.

Now, an inverter wired to engine battery over thick enough cable, powering a 20 amp charger near house batteries can work.

But the inverter should not be in engine compartment. Long thick cables to mount it away from engine heat likely means these same cables can go from alternator to solenoid to house battery and deliver more amperage if the vehicles voltage regulator decides to seek and hold voltage in the 14,s.

The inverter on engine battery powering distant 120 vac charger charging house battery makez most sense when distances are large as there is little voltage drop on AC.

Wiring a solenoid is often viewed as complex. It is not. And it is very effective when thick copper is used and battery below 80%.

Low and slow solar is not great at getting quickly to 80%, and an agm battery will be tickled to premature death in Such usage.