Charge house batteries with DC?

[cinemaphonic]

Wondering if I could charge my house batteries with a power inverter hooked up to the van's DC output, then hooked up to my 3 stage charger and to my house marine batteries? I was thinking of this as an alternative to wiring up one of those continuous duty solenoids to the starting battery.

Thanks.

 

[akrvbob]

No, each extra step you put between the alternator and the house battery wastes a lot of power. It's a very bad bad idea.

The beauty of a solenoid is it uses virtually no power at all and after you install it is as simple and easy as it can possibly be.
Bob

 

[SternWake]

There are times when the inverter on the engine battery, powering a battery charger hooked to the house batteries is acceptable, and ta few circumstances when this is preferable to a solenoid.

One of these is when the house batteries are at a great distance from the alternator. Since there is very little voltage drop on AC lines one can put a higher voltage/ current 3 stage charger on the house batteries powered by an inverter attached to engine battery and actually get increased charging current.

Also, Some vehicle voltage regulators are set too low, and combine this with long thin runs of copper to feed the distant house batteries, this method is a viable option.

However one pretty much needs a dedicated inverter very close to the engine battery, then a quality 12 gauge extension cord to feed the grid powered AC battery charging source. The extra heat under the engine compartment will shorten inverter life, water intrusion might kill it, there are 15% inefficiencies minimum on any inverter, pure sine wave or modified square wave inverter, and another 15% inefficiency in the AC/DC battery charger.

Add up the costs of this vs using 2 awg copper, or thicker the total distance between alternator solenoid and house battery and it is difficult to say which is going to be more effective without knowing all the many variables.

I personally prefer thick copper, but there are times my vehicle's voltage regulator decided 13.7v is plenty and recharging current attenuates to a large degree, compared to if the VR was allowing 14.7+ to continue.

Also if going the inverter route, one must keep in mind hot alternators are limited in their output, especially when asked to exceed their capability at slower, idle speed rpms.

If the inverter is large, and the AC/DC charger is powerful, then it is likely the alternator can not keep up, and the engine starting battery would be depleted to charge the house batteries., and modern starting batteries do not like to live their life less than 95% charged and will degrade quickly if cycled deeper than 20%( 80% charged).

So is it possible, yes, will it be cheaper and more effective? In 99% of rigs not towing a trailer, no. If an equal amount of money was spent running thick copper to distant batteries, the copper would likely be more effective, and possibly much much more effective.

But if one already has an inverter, and a quality AC extension cord, and a charger, then this can certainly work, but I would recommend saving for some good copper with proper terminals professionally attached, a high quality solenoid, as well as taking power directly from alternator to feed solenoid and house battery bank.

Taking power from engine battery leaves the original OEM charging circuit as the weak link, and tricks the voltage regulator into thinking the house batteries are more charged than they are, and cut back voltage, which cuts back charging amps.

There are dozens of ways to charge a battery and isolate house from engine batteries with the engine off. There is no one right way. I like extra copper because less can go wrong, if fused properly. I personally employ manual switches, so I dictate where charging current goes to and from, and where discharging current is taken from. But my system would confuse 99% of people at first glance and explanation of how it functions. Sometimes it is not so convenient to go and turn the switch when I want the alternator to feed the house bank, or turn it off so the house battery does not try and assist the starting battery.

 

[cinemaphonic]

There are dozens of ways to charge a battery and isolate house from engine batteries with the engine off. There is no one right way. I like extra copper because less can go wrong, if fused properly. I personally employ manual switches, so I dictate where charging current goes to and from, and where discharging current is taken from. But my system would confuse 99% of people at first glance and explanation of how it functions. Sometimes it is not so convenient to go and turn the switch when I want the alternator to feed the house bank, or turn it off so the house battery does not try and assist the starting battery.

Thanks Bob and SternWake. I already have my solenoid, but just wanted to see if this was a just as good of an option. So the solenoid gets hooked up to the alternator, not the starting battery? Sorry, no idea what I'm doing (yet).

 

[MikeRuth]

http://www.doityourselfrv.com/bring-van-camper-life-add-batteries-solenoid-stealth-rv/

Take a look at the diagram on that page. If I recall there is a good article here on this site but I haven't bookmarked it yet

 

[SternWake]

The solenoid can take power from starting battery, or alternator directly. Alternator directly is more effective for a few reasons in mentioned in the last post.

Very few diagrams will show power taken directly from alternator(+) but instead show it on the starter battery.

Taking power for solenoid directly from ALT(+) is a shortcut and will increase charging amps into depleted house bank by a good amount.

If one really wants to take it from engine battery, then run an additional cable properly fused, to engine battery (+) from alternator (+). But then one sees that there is less copper length needed to go directly from alternator to solenoid for the same function, but the much shorter circuit allows more amps to flow into a depleted battery.

If the battery is not very depleted then this is not very beneficial. But short trips can certainly accomplish a lot more.

This Cable needs to be fused properly

 

[cinemaphonic]

The solenoid can take power from starting battery, or alternator directly. Alternator directly is more effective for a few reasons in mentioned in the last post.

Very few diagrams will show power taken directly from alternator(+) but instead show it on the starter battery.

Taking power for solenoid directly from ALT(+) is a shortcut and will increase charging amps into depleted house bank by a good amount.

If one really wants to take it from engine battery, then run an additional cable properly fused, to engine battery (+) from alternator (+). But then one sees that there is less copper length needed to go directly from alternator to solenoid for the same function, but the much shorter circuit allows more amps to flow into a depleted battery.

If the battery is not very depleted then this is not very beneficial. But short trips can certainly accomplish a lot more.

This Cable needs to be fused properly

Thank you. So the alternator to house battery connection should be fused? Would a 30a breaker do the job?

 

[SternWake]

Only if you use 10 AWG

Fuse to protect wiring. Make wiring thick enough for minimal voltage drop, I'd say go no thinner than 6 awg with 4 awg preferable and 2 being even better. If alternator recharging is to be the primary and perhaps only charging source, buy more copper now or buy more lead later, when the battery fails way prematurely.

Yes thick copper cable is expensive, but so are lead acid batteries, and the frustration that goes with them failing to meet your needs at the worst possible time due to chronic undercharging caused by being scared of the price of copper in the not too distant past.

Push button circuit breakers, Maxi fuses, ANL fuses, even fusible link can be used to protect wiring.

Beware of cheap circuit breakers, they introduce way too much resistance and voltage drop, and will likely not trip at their rating.

Go for Bussman brand, if going the circuit breaker path

 

[cinemaphonic]

Only if you use 10 AWG

Fuse to protect wiring. Make wiring thick enough for minimal voltage drop, I'd say go no thinner than 6 awg with 4 awg preferable and 2 being even better. If alternator recharging is to be the primary and perhaps only charging source, buy more copper now or buy more lead later, when the battery fails way prematurely.

Yes thick copper cable is expensive, but so are lead acid batteries, and the frustration that goes with them failing to meet your needs at the worst possible time due to chronic undercharging caused by being scared of the price of copper in the not too distant past.

Push button circuit breakers, Maxi fuses, ANL fuses, even fusible link can be used to protect wiring.

Beware of cheap circuit breakers, they introduce way too much resistance and voltage drop, and will likely not trip at their rating.

Go for Bussman brand, if going the circuit breaker path

Oh boy. More and more I'm thinking I just need to hire someone to show me how to do this. Thanks though, this has been helpful.

 

[SternWake]

http://www.expeditionportal.com/for...ke-a-cheap-isolated-dual-battery-setup-for-50

A diagram is worth 3 thousand words.

Wiring a solenoid in is not overly complex, but can certainly appear to be before one does so.

I just like to stress using thicker copper and having these thicker copper cables properly terminated with quality ring terminals, for minimum voltage drop and maximum performance.

Chronic undercharging is the biggest killer of all batteries, that, and the attitude that the all mighty alternator is an instant and totally effective charging source.

The alternator can be very effective bring a depleted battery to 80% charged, but only if thick copper mates alternator to solenoid to house battery. This thicker copper also allows the vehicles voltage regulator to "see" a depleted battery, and allow higher voltages to continue for longer, charging the battery faster, as voltage is electrical pressure. The higher the pressure, the more amps can flow.

The more amps can flow, the faster the battery recharges.
The faster the battery recharges, the closer it returns to full charge
The closer it returns to full charge each drive, the longer the battery will last, and the better it will perform during that lifespan.

On the above link there is a prominent poster. DWH, who knows his stuff, but we disagree on thick copper being necessary.
He is wrong, and obstinately so. You want 4 awg, and you want this 4awg to have good terminations.

properly terminating large cables requires skill and tools. Better the Novice have quality cables professionally made.

Once one figures out the lengths of copper needed:
http://www.genuinedealz.com/custom-cables

These are among the best prices you will find for top quality cabling anywhere. What you spend on these cables, will be saved in terms of buying less batteries in the future.
Finding your battery dead can be stressful, and getting them back to their full remaining capacity is a chore, and rarely occurs, and the battery is replaced shortly after, only to have the next one start suffering the same fate. Batterycide through chronic undercharging.