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Author Topic: Charging house battery  (Read 439 times)

Ryderbike

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Charging house battery
« on: March 14, 2019, 08:53:55 PM »
I would like feedback on my house battery charging.

I have a 10 gauge wire running from my starting battery to a battery switch with a 30amp fuse close to the battery. Then I ran from the battery switch to my house battery. When the switch is on of course the batteries are connected and my alternator can charge the house battery. When the vehicle is not running I turn off the battery switch so the starting battery doesnít get used.

I donít have any contact switches ,relays etc, so I wanted to make sure I havenít done anything wrong,

Thanks

Tom_M

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Re: Charging house battery
« Reply #1 on: March 15, 2019, 06:27:47 AM »
There's nothing wrong with your approach unless you forget to disconnect and run your start battery down. It would be fairly easy to replace your switch with a continuous duty solenoid. Also I would suggest going with larger wire.
Tom
2005 Born Free 24 Rear Bath
Towing 2013 Smart Car

ClassyC

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Re: Charging house battery
« Reply #2 on: March 15, 2019, 07:06:54 AM »
You can buy a battery isolator.  I assume you are aware of these since you referred to them, but just in case hereís a video intro
https://m.youtube.com/watch?v=CGD8HAeg5UA
I ran a diode based isolator on a previous truck for over 10 years with no issues.

Henry J Fate

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Re: Charging house battery
« Reply #3 on: March 15, 2019, 07:10:54 AM »
I would size the interconnecting wire large enough to carry the load of the starter. If you leave the switch in the position which connects both batteries and then start your engine, current draw from the house battery could be quite large depending on battery conditions and blow the 30 amp fuse. The fuse protects the wire from burning up and 30 amps would be fine unless the length of wire is excessive. If you want to isolate the house battery from the starting circuit, a relay would be best and wired so that when the ignition is in the starting position, it removes the house batteries from the circuit and draws solely off the starting battery. This would prevent the possibility of blowing the 30amp fuse when starting the engine.

Hope that helps

Henry

Gary RV_Wizard

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Re: Charging house battery
« Reply #4 on: March 15, 2019, 08:27:38 AM »
Your design is fine, but my question is why do you need that?   All coaches are designed with circuitry that performs that function (charging house battery from alternator).  If it's not working, you probably have a bad isolator device or isolation relay.
Gary
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Gary Brinck
Summers: Black Mountain, NC
Home: Ocala National Forest, FL

Ryderbike

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Re: Charging house battery
« Reply #5 on: March 16, 2019, 02:34:58 AM »
Your design is fine, but my question is why do you need that?   All coaches are designed with circuitry that performs that function (charging house battery from alternator).  If it's not working, you probably have a bad isolator device or isolation relay.


My camper is a bus conversion. I built everything myself and installed my own electrical system.
« Last Edit: March 16, 2019, 07:20:59 AM by Back2PA »

kdbgoat

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Re: Charging house battery
« Reply #6 on: March 16, 2019, 06:12:19 AM »
Gotcha  8). Now you have us waiting for pics ;D
I know you believe you understand what you think I said,
But I am not sure you realize what you heard is not what I meant

2012 Redwood 36RL
2016 Leprechaun 319DS

Gary RV_Wizard

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Re: Charging house battery
« Reply #7 on: March 16, 2019, 08:59:35 AM »
It's easy to use a solenoid to avoid the "forgot to disconnect) problem. A simple solenoid that is activated by the ignition 12v will close the circuit whenever the engine is running and leave it open otherwise. A solenoid that can handle 30A should be inexpensive.

There is another potential problem inconvenience here: the 30A wire capacity.   If the house batteries are substantially discharged, say below the 50% level, odds are the amps flowing to them will exceed 30A and blow that fuse (to protect the wiring).  If you want to stay with 10 gauge wiring, I'd use a circuit breaker instead of a fuse so that its easy to reset.
Gary
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Gary Brinck
Summers: Black Mountain, NC
Home: Ocala National Forest, FL

Ryderbike

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Re: Charging house battery
« Reply #8 on: March 16, 2019, 09:03:51 AM »
It's easy to use a solenoid to avoid the "forgot to disconnect) problem. A simple solenoid that is activated by the ignition 12v will close the circuit whenever the engine is running and leave it open otherwise. A solenoid that can handle 30A should be inexpensive.

There is another potential problem inconvenience here: the 30A wire capacity.   If the house batteries are substantially discharged, say below the 50% level, odds are the amps flowing to them will exceed 30A and blow that fuse (to protect the wiring).  If you want to stay with 10 gauge wiring, I'd use a circuit breaker instead of a fuse so that its easy to reset.

I carry lots of fuses but I may take your advice and get a breaker.

I am familiar with all the different solenoids,relays,etc but I just wanted everyoneís opinion on whether they saw any potential problems with my basic manual set up.

Thanks again

Henry J Fate

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Re: Charging house battery
« Reply #9 on: March 17, 2019, 12:49:11 PM »
Just wanted to add additional info....

The possibility of exceeding the 30 amp fuse is fairly certain. This will occur in a least two ways. The house batteries drawing more than 30 amps for charging and the starter (which will draw 100s of amps) drawing over 30 amps when starting the vehicle. There are several conditions that will cause either of the two but it is fairly certain that the circuit will be over drawn and under designed.

Generally when designing a circuit, it should be designed and geared for the amps that it will carry. Continuously placing the circuit in an overloaded condition is not practical and could be considered unsafe. The wire size and design should be geared for what the current will be at its highest level which in this case would be the starter. The charging circuit could also be of issue. Another thing to keep in mind is that if the charging current exceeds the 30 amps and either the breaker trips or the fuse blows, how and when would you expect the current draw to decrease below the 30 amps so that the fuse doesn't blow or the breaker doesn't trip and you are able to charge the battery off the engine alternator? One other note... Placing a solenoid in the ignition circuit to disconnect the house battery would effectively negate the ability to charge the house battery off the alternator which I assumed was your intended result.

I would suggest to spend some additional thought into this before settling on a design. I would not be comfortable leaving it as it currently is. It should be designed so that fuses and breakers do not blow or trip unless of course there is a malfunction that is out of the designers control

Hope this helps and good luck.

Henry







Ryderbike

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Re: Charging house battery
« Reply #10 on: March 17, 2019, 01:25:05 PM »
Just wanted to add additional info....

The possibility of exceeding the 30 amp fuse is fairly certain. This will occur in a least two ways. The house batteries drawing more than 30 amps for charging and the starter (which will draw 100s of amps) drawing over 30 amps when starting the vehicle. There are several conditions that will cause either of the two but it is fairly certain that the circuit will be over drawn and under designed.

Generally when designing a circuit, it should be designed and geared for the amps that it will carry. Continuously placing the circuit in an overloaded condition is not practical and could be considered unsafe. The wire size and design should be geared for what the current will be at its highest level which in this case would be the starter. The charging circuit could also be of issue. Another thing to keep in mind is that if the charging current exceeds the 30 amps and either the breaker trips or the fuse blows, how and when would you expect the current draw to decrease below the 30 amps so that the fuse doesn't blow or the breaker doesn't trip and you are able to charge the battery off the engine alternator? One other note... Placing a solenoid in the ignition circuit to disconnect the house battery would effectively negate the ability to charge the house battery off the alternator which I assumed was your intended result.

I would suggest to spend some additional thought into this before settling on a design. I would not be comfortable leaving it as it currently is. It should be designed so that fuses and breakers do not blow or trip unless of course there is a malfunction that is out of the designers control

Hope this helps and good luck.

Henry

Henry ....you are correct the fuse will blow ONLY if I have it connected to the starting battery when I start the vehicle and then only if the starter batteries are low.
. It will not blow during the charging cycle. If you check out an rv trailer you will find the charge line never exceeds 10 gauge.

I donít intend to use the house battery as a back up starting battery,

Thx for your comment,,,

Henry J Fate

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Re: Charging house battery
« Reply #11 on: March 17, 2019, 05:28:39 PM »
Maybe the diode design that was earlier suggested by Classyc may be the way to go. That would prevent the flow of electricity from the house battery to the starting battery but allow charging from the alternator. One other thought... I would assume the alternator isn't sized for charging house batteries unless you changed it with something else. That could keep your incoming charge amps to the house battery lower than what would be expected of an alternator built for that type of duty. So it could work out the the alternator never exceeds your circuit capacity. Also... Gary's suggestion of adding a solenoid to connect the batteries for charging seems to be a good one. I miss-understood what Gary was suggesting initially. That design is commonly used or was commonly used. The problem with that design in modern moterhomes with auxillary power hook up provisions, your starting battery is eliminated from the circuit thus isolating it from any charging circuit that would be available. My coach was one of those vehicles and it was a problem that needed to be rectified. So in your case assuming you will not be hooking up to auxillary power and would not have a converter charger on board, Gary's design would be perfect as I believe the start position on the ignition switch would not combine the batteries. The solenoid would only close to combine the batteries in the run position. Adding an auxillary switch to that solenoid would provide a way to combine the batteries independent from the ignition switch and eliminate the manual switch.

Food for thought. Hope to see this project. Good luck.

Henry

ClassyC

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Re: Charging house battery
« Reply #12 on: March 17, 2019, 05:30:59 PM »
That is why I brought up the isolator.  For $20-30 its an inexpensive way to insure you donít backfeed when starting.


Gary RV_Wizard

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Re: Charging house battery
« Reply #14 on: March 18, 2019, 09:45:08 AM »
Quote
If you check out an rv trailer you will find the charge line never exceeds 10 gauge.
That doesn't mean it cannot try to draw more and blow the fuse.  I'll grant, though, that single 12v battery in the size 24-31 range is very unlikely to ever draw more than 30A when charging.   Add a second battery to the house bank, though, and all bets are off. Been there & done that!
Gary
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Gary Brinck
Summers: Black Mountain, NC
Home: Ocala National Forest, FL

Ryderbike

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Re: Charging house battery
« Reply #15 on: March 18, 2019, 10:01:12 AM »
That doesn't mean it cannot try to draw more and blow the fuse.  I'll grant, though, that single 12v battery in the size 24-31 range is very unlikely to ever draw more than 30A when charging.   Add a second battery to the house bank, though, and all bets are off. Been there & done that!


I appreciate your advice.

Thnx