12v not working

Paul · June 04, 2021, 08:09:10 PM

Hi, I am currently hooked up to power with my 21bhs and I don't have 12v power. When I test with a multimeter at the battery it says 4.86V. I looked at all of the fuse and they seem fine and all the breakers are on. 120v power works fine. The refrigerator lights are on but it doesn't work and the check light is on.

Any ideas?

GrampaKilt · June 04, 2021, 08:38:59 PM

Hi Paul, if 4.86V is the reading, I would conclude your battery has no energy left and probably need replacing. For example, when a lead acid (LA) battery reads 12.1V it is already 50% discharged and should be recharged. I'm told that by about 10V, an LA battery is essentially dead. Yours is 'dead/dead' $:-\$ . Fully charged batteries run voltages in the 13-14V range depending on age.

A suggestion, if you are running a single 12V battery, this is a good time to upgrade to 2 deep cycle 6V batteries hooked up in series. Costco has the best price. When I last checked, they provided 208 amp hours (Ah) of power. (In reality, you would only want to use up half those Ahs before recharging.) Regards, GK

charliem · June 04, 2021, 08:42:49 PM

Paul,
Obviously the battery is dead and probably damaged. With 4+ volts nothing will work. My guess is the onboard converter is not charging at all and not supplying 12V. Check the two 30A battery reversal fuses on the converter. They will blow if the battery is reversed even for an instant. As I recall the reversal fuses will isolate the converter while leaving the rest of the 12V distribution panel connected to the battery. If true the battery will not charge and nothing on the12V system will work after the battery in discharged. There is also the possibility that the converter itself is bad. Not sure what brand you have but the old WFCO units had a pretty bad reliability reputation.

Paul · June 04, 2021, 09:11:41 PM

I looked again at the fuse and there is one 40A labeled as reverse polarity that seem blown. If I change it will the 12v system still work with a damaged battery? Or should I replace the battery first

charliem · June 04, 2021, 09:43:00 PM

Paul,
I would at least charge the battery before reconnecting it. The high inrush current of a totally depleted battery might blow the fuse again. Replacing the battery is your call. My guess is it's damaged but it might work well enough for you while shore power is available. That said you MUST verify the polarity before you reconnect. Do this with a voltmeter and Mark the battery leads so you'll be certain next year. RVs seem to utilize a mix of residential (white negative) and automotive (black negative) color coding. The voltmeter is your savior.

Paul · June 04, 2021, 10:30:43 PM

Quote from: charliem on June 04, 2021, 09:43:00 PM
Paul,
I would at least charge the battery before reconnecting it. The high inrush current of a totally depleted battery might blow the fuse again. Replacing the battery is your call. My guess is it's damaged but it might work well enough for you while shore power is available. That said you MUST verify the polarity before you reconnect. Do this with a voltmeter and Mark the battery leads so you'll be certain next year. RVs seem to utilize a mix of residential (white negative) and automotive (black negative) color coding. The voltmeter is your savior.

Hi Charlie, the color is red and black, currently I have the red on the positive and black on the negative. I can bring the battery home to charge it than reconnect just to get me going while I shop for a new battery.

Thanks!

Pinstriper · June 04, 2021, 11:23:45 PM

If the battery were removed entirely, I would think you would have 12v while on shore power, so if you don't and the breakers and fuses are all straight, your converter is biffed. That would also result in the reading you are getting. There's just nothing left in the battery, and nothing coming from the converter.

If the converter were good, and the battery just bad, you should get charging voltage levels across the terminals (14v+) while connected to shore power.

charliem · June 05, 2021, 12:48:14 PM

Quote from: Pinstriper on June 04, 2021, 11:23:45 PM
If the battery were removed entirely, I would think you would have 12v while on shore power, so if you don't and the breakers and fuses are all straight, your converter is biffed. That would also result in the reading you are getting. There's just nothing left in the battery, and nothing coming from the converter.

If the converter were good, and the battery just bad, you should get charging voltage levels across the terminals (14v+) while connected to shore power.

Maybe and maybe not. As I recall the battery reversal fuses protect the converter by isolating it but leave the rest of the 12V loads connected to the battery. If so, and the reversal fuse was blown, the battery would drain to zilch and no charging voltage would be present anywhere; at the battery or inside the camper.

Paul · June 05, 2021, 01:31:08 PM

Last time I went to the trailer I noticed that the radio wasn't working but there was still enough power to open the lights, probably the reversal fuse was already blown

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GrampaKilt · June 05, 2021, 01:51:27 PM

What a great forum this is. Thanks for managing it, Paul! So many knowledgeable contributors. I grimace remembering a few years when I assumed a red plastic cap on a battery terminal was the +ve...and couldn't figure out why my 12 volt lights quit working and the 2 fuses on the converter kept blowing. GK

Paul · June 05, 2021, 08:50:00 PM

Quote from: GrampaKilt on June 05, 2021, 01:51:27 PM
What a great forum this is. Thanks for managing it, Paul! So many knowledgeable contributors. I grimace remembering a few years when I assumed a red plastic cap on a battery terminal was the +ve...and couldn't figure out why my 12 volt lights quit working and the 2 fuses on the converter kept blowing. GK

Thank you!

Paul · June 08, 2021, 10:55:59 PM

I had a very hard time finding a 40a fuse locally, all I could find was 30a. I could have looked harder though just went to 3 stores. I decided to order a pack on amazon. I went to Canadian Tire and got a AGM group 24 battery. I didn't wanted to go up in size or switch to 6v batteries since I didn't wanted to change the box etc. and a group 24 is enough for my need but I decided to upgrade to AGM.

My radio is not working though I though maybe it was because of the blown fuse or that the old battery wasn't charged enough but it still doesn't work with the new battery, everything else work fine.

GrampaKilt · June 08, 2021, 11:12:09 PM

Hmmm, my converter protection fuses are 30A. I'm not sure if that's because shore power is 30A max or if that fuse rating is just a coincidence. BTW, check the radio's own fuse, 5A??; one has to remove the radio to get at it. Regards, GK

Pinstriper · June 09, 2021, 12:27:02 AM

Quote from: GrampaKilt on June 08, 2021, 11:12:09 PM
Hmmm, my converter protection fuses are 30A. I'm not sure if that's because shore power is 30A max or if that fuse rating is just a coincidence. BTW, check the radio's own fuse, 5A??; one has to remove the radio to get at it. Regards, GK

The fuse will be sized for the gauge of wire and the device it protects. It is possible Paul's fuse was replaced by someone who didn't want the 30 to blow (when in fact it was designed to).

Paul · June 09, 2021, 07:22:33 AM

Quote from: GrampaKilt on June 08, 2021, 11:12:09 PM
Hmmm, my converter protection fuses are 30A. I'm not sure if that's because shore power is 30A max or if that fuse rating is just a coincidence. BTW, check the radio's own fuse, 5A??; one has to remove the radio to get at it. Regards, GK

Thank you I will check that

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