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Old 01-01-2021, 06:25 PM   #1
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THOR #1765
Emergency Start/Battery Booster Switch

For all my electrical savvy friends out there... I have a Class B which is set up so the house batteries are charged by both the engine alternator or shore power/generator/solar panels but the chassis battery is only charged by the engine alternator. However I do have a “Battery Boost” switch which connects the chassis battery to the house batteries. My solar panels keep the house batteries at full charge all the time, but the engine battery degrades slowly.
My question - is there anything negative with taping the Battery Boost switch in the “on” position for half a day to let the solar panels charge up the chassis battery? I obviously do not want to do it permanently and i am not sure I want to do it if I am on shore power, but I cannot see any problem with temporarily taping the switch open using just the solar panels.

Thoughts?
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Old 01-01-2021, 07:35 PM   #2
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I suspect that if you tape the boost switch closed, you will eventually burn out the relay coil. It probably is not designed for continuous use.

David
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Old 01-01-2021, 07:47 PM   #3
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Could you just throw a jumper cable around that switch; for short term usage?
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Old 01-01-2021, 09:06 PM   #4
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Another thought: Leaving the battery boost switch on 24/7 will cause a continuous draw of several amps (power to the relay) that may be more than your solar system can keep up with.

Jumpering as Bob suggests shoud work as a long term storage solution. Go to a boating parts store like West Marine (the Camping World of boating) and buy a 12-18" jumper and hook it up between the two battery systems, ie across the solenoid.

David
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Old 01-01-2021, 09:10 PM   #5
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Originally Posted by DavidEM View Post
I suspect that if you tape the boost switch closed, you will eventually burn out the relay coil. It probably is not designed for continuous use.

David
If I was running 30-55 Amps thru it, I would agree - that’s why I would not do it while running the generator or under shore power. But I am not sure that the amperage from the solar panels is large enough to burn out the coil. But, you are right, unless I am sure, I sprint want to burn it out.
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Old 01-01-2021, 09:17 PM   #6
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Originally Posted by Bob Denman View Post
Could you just throw a jumper cable around that switch; for short term usage?
In my Winnebago Travato, the two AGM batteries are positioned on top of the rear axel and have about 1” of clearance on top. I guess I could run a jumper from the coach battery side of the coil that closes when the alternator charges the house batteries. But I dont think it is worth screwing with that system.

I guess the easiest thing is to continue to run the engine every week or so and charge it up, or hook up a small solar panel to the engine battery.
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Old 01-01-2021, 09:21 PM   #7
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Originally Posted by DavidEM View Post
Another thought: Leaving the battery boost switch on 24/7 will cause a continuous draw of several amps (power to the relay) that may be more than your solar system can keep up with.

Jumpering as Bob suggests shoud work as a long term storage solution. Go to a boating parts store like West Marine (the Camping World of boating) and buy a 12-18" jumper and hook it up between the two battery systems, ie across the solenoid.

David
I don’t intend to leave it in 24/7. It sits in my yard, so I can just leave it on during the day - once a week. The 200 watts of solar panels keeps the two AGM batteries full all the time, so I don’t think they would have any problem topping up the engine battery - during sunny daylight in south Florida.
Thanks for the thoughts.
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Old 01-01-2021, 09:26 PM   #8
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Sounds like you have a timed isolation circuit which allows the engine to charge the house batteries when running. That circuit operates the same relay that the emergency start switch operates. The relay is made to stay energized for long periods. So you will not burn it out as you were told.

Yes you could do what you asked but if coach batteries discharge so will your chassis battery.
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Old 01-01-2021, 09:43 PM   #9
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Sounds like you have a timed isolation circuit which allows the engine to charge the house batteries when running. That circuit operates the same relay that the emergency start switch operates. The relay is made to stay energized for long periods. So you will not burn it out as you were told.

Yes you could do what you asked but if coach batteries discharge so will your chassis battery.
Thanks for the comment. I thought that might be the case - that the “battery boost” and alternator to house batteries might be the same relay. That makes sense - why have two or make it any more complicated. I would not leave the switch taped down for more than half a day (if that long) and I could routinely check it, so I am not worried about discharging the house batteries. I guess I will give Winnebago a call and see what they say. The people there seem pretty knowledgeable.
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Old 01-01-2021, 10:08 PM   #10
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Originally Posted by Oneilkeys View Post
If I was running 30-55 Amps thru it, I would agree - that’s why I would not do it while running the generator or under shore power. But I am not sure that the amperage from the solar panels is large enough to burn out the coil. But, you are right, unless I am sure, I sprint want to burn it out.
It is not the charging current that goes to the battery I am speaking of. That goes through a set of contacts and should be good indefinitely. I am speaking of the current that goes from the switch to the relay coil that pulls those contacts in. That coil may not be designed for continuous use.

Re my second post: That coil can draw 5 amps or so. Your solar panels in direct sun might put out twice that but only for a few hours each day. Before 10:00 and after 2:00 you may be getting less than nothing to the chassis battery.

David
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