Low Voltage battery cut off???!!! - Fiberglass RV


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Old 06-15-2012, 03:54 PM   #1
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Low Voltage battery cut off???!!!

I want a device I can put on/near my battery that will cut off the power from the battery when voltage drops too low, thus preventing a complete discharge.

I'd expect to see these available everywhere 12V batteries are sold, yet I can't find them anywhere at all.

The battery I bought last fall seems 100% dead and I'm not sure why. Perhaps the guy who wired my new brakes in left a short somewhere. Or I left a light on, but the only lights that might have been on are LED and I'd expect them to take over a week to drop that battery from over 12V to below the 8v at the low end of my meter's scale. It was around 12V one night, completely dead in the morning. 30 minutes charging from my car @14v and still reading under 8V. So I assume it's dead.

I assume some battery maker has a patent and won't let make anyone make any devices to do this because it would mean millions of less dead batteries, thus millions less battery sales every year???

Heck, every battery should have one of these built in from the factory!!! It couldn't cost more than a few bucks for such a protection circuit if made by the thousands/millions.
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Old 06-15-2012, 04:13 PM   #2
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Originally Posted by dylanear View Post
30 minutes charging from my car @14v and still reading under 8V. So I assume it's dead.
Suspect it will take way longer than 30 min for the car to do much in the way of recharging a dead battery. You may want to put it on a charger overnight before declaring it dead or plugging into 110 for a night & let the converter take care of it.

When running on battery I have a cheap little plug in monitor that has a light that will come on as well as a little alarm if the battery gets to 40% discharge.
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Old 06-15-2012, 04:28 PM   #3
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here is what you are looking for $70
LVD 12, 12V Low Voltage Disconnect
I may get me one of these myself
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Old 06-15-2012, 04:39 PM   #4
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Low voltage disconnect is a common feature in solar controllers, as well. Might be a cheaper route.
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Old 06-15-2012, 04:55 PM   #5
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Low voltage disconnect is a common feature in solar controllers, as well. Might be a cheaper route.
I thought I saw that as a feature on a fairly high end controller, don't recall what brand or anything. Any recommendations down in the budget range?
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Old 06-15-2012, 05:02 PM   #6
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I thought I saw that as a feature on a fairly high end controller, don't recall what brand or anything. Any recommendations down in the budget range?
Maybe this one? Amazon.com: HQRP Solar Power Controller 10Amp 150W with Digital LED Display plus HQRP UV Chain / UV Radiation Health Tester: Patio, Lawn & Garden
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Old 06-15-2012, 06:20 PM   #7
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Umm you mean the one I was just planning to order and reading about??? At the rate my mind is failing today I better hit map quest before pulling the car in the garage.

A cut off at 11.1 volts is essentially a 100% dead battery right? 12.1 makes more sense and that would be below 50 percent. Wonder if it is a typo?
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Old 06-15-2012, 06:42 PM   #8
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My Silverado came with one from the factory - It don't work.
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Old 06-15-2012, 06:47 PM   #9
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Umm you mean the one I was just planning to order and reading about??? At the rate my mind is failing today I better hit map quest before pulling the car in the garage.

A cut off at 11.1 volts is essentially a 100% dead battery right? 12.1 makes more sense and that would be below 50 percent. Wonder if it is a typo?
Dunno. Time to trot out the electronics experts. This Morningstar disconnects at 11.5 volts. I look to Morningstar to be a leader in engineering solar chargers, so maybe disconnect voltage is different than stabilized voltage in inferring state of charge?

Amazon.com: Morningstar SHS-10 Solar Controller 10 Amp 12 Volt 170 Watts: Electronics
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Old 06-15-2012, 07:05 PM   #10
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If you want cheap, these solar controllers have a built in cut off and are only $11. If you can solder, you can even add a second set of mosfets to double the amperage they can handle.
Solar Panel Charger Regulator Controller 10A/12V/24V Safe Protection CE Certify | eBay
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Old 06-15-2012, 07:38 PM   #11
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It's not a good idea to leave a battery sitting without at least a trickle charger for long periods of time. Batteries will be discharged in about 3 to 4 months just sitting by themselves. If your trailer sits in a storage lot, remove the battery when not in use. Take it home and connect it to a Battery Minder or some other similar trickle charger. Make sure the charger has a desulfate mode.
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Old 06-15-2012, 07:38 PM   #12
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I had a co-worker that used to nod off in his car at parties and such with the radio going, only to wake up with a dead battery. He whipped up some radio shack parts and made a low voltage cut off just for the acc. circut.

Was just a little plastic project box under his dash.
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Old 06-15-2012, 09:11 PM   #13
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It's not a good idea to leave a battery sitting without at least a trickle charger for long periods of time. Batteries will be discharged in about 3 to 4 months just sitting by themselves. If your trailer sits in a storage lot, remove the battery when not in use. Take it home and connect it to a Battery Minder or some other similar trickle charger. Make sure the charger has a desulfate mode.
I guess I didn't read thoroughly enough. I didn't see where the battery went dead in one night.
The first thing I would do is charge the battery with a battery charger, then take it to someplace that can do a load test. Many battery shops will charge and do a load test without a fee. Even if there is a small fee it's worth it to tell what shape the batteries in.
If this just happened and the battery has been in the trailer for several months and I couldn't find anything on, I would suspect the battery first.

I strongly suggest you track down the cause before attempting a fix. You might be fixing something doesn't need fixing.
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Old 06-15-2012, 09:17 PM   #14
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One of the problems with low voltage cut circuits (switches) they draw power from the battery. Some of circuits I looked at will continue to draw current even after they've disconnected the battery from everything else.

It's always a good idea to know what caused the battery discharge.
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Old 06-15-2012, 10:38 PM   #15
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For about $35 you can get a VoltMinder (voltminder.com) that will provide an accurate indication of voltage as well as has an alarm that is real noisy when it gets down to the voltage you select.



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Old 06-16-2012, 04:04 AM   #16
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I have gotten in the habit of periodically checking my battery. If you check it when you stop for the night and again in the morning you can easily keep track of how well your system is working. Best to measure right at the battery. Twenty bucks for a multimeter. Raz
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Old 06-17-2012, 04:30 PM   #17
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Thanks for all the suggestions. I have been looking at charge controllers and saw that feature. I'm learning towards a Morningstar 10 amp.

Thing is, all 12V power would need to be wired through the controller?

I'm unclear how the AC to DC charging system would work together with the solar charge controller. And then I'd like a high end AC 12V charger as well, with advanced conditioning/desulfication modes. Ideally there's be one box, or boxes made to work together to do all this. Heck, if it had a 500watt inverter on there too I'd be sold!

Definitely will be looking to find out how it got discharged. I was on AC all winter and thus the battery had at least basic charging/conditioning all the time. It did sit for 3+ days at the shop getting it's new axle and brakes. Perhaps they left lights on. But it had lighting (LED) and I believe a reasonable voltage reading the day I picked it up. And a deeply discharged, if not dead battery the next day.

There's only 20 RV shops within a mile of me this week. So there's help to be had. Hopefully I can find a good one who can help me find some good solar charging and will sort all my electronics issues at the same time.
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Old 06-17-2012, 05:55 PM   #18
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Dylan,

I expect that the Solar 30 solar panel controller I've shown on the following FVR could detecT Battery Voltage and automatically disconnect load when the voltage reaches a preset level. As well the controller allows you to preset the voltage level.

If you don't have solar panels, you would have to trick the controller into believing a panel is attached/

http://www.fiberglassrv.com/forums/f...-48167-14.html
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Old 06-19-2012, 11:18 AM   #19
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I need to tattoo, "K.I.S.S." (Keep it simple stupid!) on my forehead.

I'm not sure what's going on with the meter/the trailer's wiring. But I measured 12.56V at the battery terminals yesterday. (After buying a Battery Tender) So I think the battery is good, I may just have some wiring to debug.

I'll be needing to go over the wiring anyway. I've never been clear on just how the whole thing is wired in front. I've replaced the AC/DC converter/fuse box in back so I know all that wiring OK, but not the wiring around the front. I'll be ripping that area apart in the next few days, so I'll take a look.

Thanks all, I'll still be wanting discharge protection, so all the discussion is still helpful even if I haven't killed the battery.

One more thing. I'd like to add a second battery, hopefully in back by the AC/DC box under the seat. Will this be a pain, using one solar controller on two batteries 8 feet apart? One inside, one outside getting hotter/cooler? Perhaps worth it's own thread, certain a little searching on here. Surely adding a battery has come up before.
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Old 06-19-2012, 11:28 AM   #20
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You may be reading what is called "surface charge". Put a 10 amp load on for 10 minutes and see whats happening when you take the load off.
If the converter is on and charging you should see about 13.2 volts. A charger can only charge if it's voltage is higher than the batteries.



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