Battery Disconnect

dave961 · 07-22-2018, 07:03 AM

Years ago I replaced the factory battery with a really good AGM unit. Earlier this year it became apparent that my AGM was showing its age when I couldn't start the generator while boondocking. When parked at my house I left the camper plugged into shore power all the time. I'm now thinking that is the reason my AGM is failing. I want to leave the camper plugged in, but don't want the battery charging all the time. I'm unsure if the factory battery disconnect will accomplish this, so I am going to add a disconnect switch out by the battery.

I have been reading up on several FROG posts about it. I've seen some people state you can put the switch on either side of the battery. I wonder if this is correct, since some items on the trailer ground to the frame, not the battery. Seems to me the positive post is the correct place for the additional switch. Thoughts?

SeaDog · 07-22-2018, 08:27 AM

Myself I would place the disconnect on the positive side of the battery.

Could your actual problem be battery age and not being plugged into shore power? Something I realized about battery disconnect. I have my rig plugged in and the frig on electric with things inside it. I used to disconnect my battery so it wasn't on charge from the converter then I realized if I loose power at my shop the frig will not switch to propane (no 12V) and i will loose the contents in the frig. just something to think about

CHICKDOE · 07-22-2018, 08:49 AM

have you verified the operation of the factory installed battery disconnect? their purpose is to disconnect the batteries, though many still leave some small loads. but almost for sure, it will disconnect the batteries from the converter / charger. if this is what you want to accomplish there should be no need to install your own.

Duckogram · 07-22-2018, 09:18 AM

There is a recent thread on this subject (http://www.forestriverforums.com/for...ml#post1832883) with over 130 posts (opinions) on the subject. The thread is closed because of the hostilities it evoked. Now you want to ask the exact same question! Good luck.

boondocking · 07-22-2018, 12:23 PM

Putting the disconnect on either positive or negative will accomplish the same thing. It will open the closed circuit to the battery so no little electrons can flow either direction.

NMWildcat · 07-22-2018, 12:25 PM

Here we go again

dave961 · 07-22-2018, 05:47 PM

Sorry, did not mean to start a ruckus!

dave961 · 07-22-2018, 05:50 PM

Quote:

Originally Posted by CHICKDOE

have you verified the operation of the factory installed battery disconnect? their purpose is to disconnect the batteries, though many still leave some small loads. but almost for sure, it will disconnect the batteries from the converter / charger. if this is what you want to accomplish there should be no need to install your own.

Yes, that is what I am trying to accomplish. Thanks for the reply, but the 'manuals' I got with the unit were of no help. I don't know how to verify if the battery disconnect inside will or won't stop the battery charging while on shore power. I just bought another $300 battery and don't want to toast it in 3 years.

NMWildcat · 07-22-2018, 06:05 PM

Go to harbor freight and get the cheap (or free) multimeter to check your batteries charge. It will then be evident when the battery is being charged.

ScottBrownstein · 07-22-2018, 06:09 PM

Quote:

Originally Posted by NMWildcat

Go to harbor freight and get the cheap (or free) multimeter to check your batteries charge. It will then be evident when the battery is being charged.

Agree. On most units the converter powers the DC panel and from there it goes through the disconnect to the battery bank. The coach will work when connected to shore power even with the disconnect switch off.

But easy to verify with a meter.

dave961 · 07-22-2018, 06:13 PM

OK, thanks. I'll try that.

CHICKDOE · 07-22-2018, 08:55 PM

very easy to test with a cheap (<$10) multimeter that you can get at any hardware or auto parts store. to do this you have to be plugged into shore power. set the range to DC volts and measure the dc voltage at the battery terminals. write down the number and next to it note the position of the disconnect switch. turn the switch to the other position and remeasure the voltage at the battery terminals. whichever reading is higher is the one that has the batteries connected to the charger. the lower reading has the batteries disconnected from the charger.

do you have a disconnect switch with the red thing that looks like a plastic key? if so, if the red key will come out of the switch that is the disconnect position. if you put the key back in and turn it 90 degrees it will not come out of the switch. this is the batteries connected position. (this of course assumes that it was wired properly at the factory).

get the multimeter. you will use it for many purposes.

TitanMike · 07-22-2018, 09:30 PM

Personally I'd leave the unit plugged in and the battery charging. Check the float voltage when the battery is fully charged and make sure it's not too high and causing battery to gas excessively and loose water.

Lead Acid Batteries (including AGM's) have a finite life both in discharge/charge cycles and age. Nothing will change that. Just make sure you recharge as soon as possible, not letting battery sit in a discharged state for any length of time. Make sure the converter/charger's voltage is correct for Float/Storage.

Then just put a couple bucks in the jar every time you discharge the battery so when it gets weak you'll already have it's replacement paid for.

This is one redeeming factor of Lithium batteries. Their cost is astronomical compared to lead acid but they will have much higher charge cycle lives.

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