Low-Voltage Disconnect - Anyone Using One? - Fiberglass RV

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Old 10-04-2007, 09:45 AM   #1
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Name: DK
Trailer: 2006 Escape
Posts: 19
I am considering installing a low-voltage disconnect (LVD) to ensure the battery isn't drawn down below its nominal discharge voltage, usually 11.8 volts for lead-acid batteries. When the battery reaches this predetermined voltage, the LVD disconects the battery from the load(s) until it it recharged. This extends the life of the battery significantly.

We have an LED panel in our Escape that indicates the general level of charge (charged, good, fair, bad) but it's only a general indicator and the actual voltage value is what's important. I'm also kicking around tha idea of installing both an amp meter and a volt meter, likely digital, to more accurately monitor the battery condition but that's going to be a bit more involved <g>.

Is anyone using one of these LVD units? I'd like to hear any comments, pro or con. Although I'd likely build my own, brand names, prices etc. would also be helpful.


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Old 10-04-2007, 01:06 PM   #2
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Name: Brian
Trailer: Boler (B1700RGH) 1979
Posts: 5,000
I have not used one for the trailer, only a small portable unit when running a cooler from my van. That portable unit works poorly, but I like the general idea, and think a properly designed and built trailer-scale unit would be worth considering.

In the design, I would want to avoid two features:
  • a semiconductor design which requires current to pass through a junction (such as a diode or transistor) causing a voltage drop of even a fraction of one volt
  • a solenoid which must be continuously energized to keep the power on
  • triggering logic which would turn off power, turn it back on when the battery recovers to resting voltage, and then cycle between these states
The first two of these would be undesirable to me because they would waste some of the limited available energy.

1979 Boler B1700RGH, pulled by 2004 Toyota Sienna LE 2WD
Information is good. Lack of information is not so good, but misinformation is much worse. Check facts, and apply common sense liberally.
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Old 10-04-2007, 05:22 PM   #3
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Name: Roy
Trailer: 1972 boler American and 1979 Trillium 4500
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Is anyone using one of these LVD units? I'd like to hear any comments, pro or con. Although I'd likely build my own, brand names, prices etc. would also be helpful.

I am considering one. The Coleman solar light kit I just bought comes with a Phocos charge controller that has a LVD built in. Problem is it is designed for a +ve ground system. I should be able to use it on my -ve ground trailer with a "floating ground". (Brian BP tried to explain to me, it made sense at the time, but I can't really explain it to you).

The sales manager for Phocos USA responded to my technical query within a few working hours. His response said it could be used in a -ve ground system if I took certain steps, but they do have a -ve ground controller with LVD that is currently in production and expected to hit the NA market this month (Oct. 2007). It has an optional remote digital display that will work with it. BTW ICP aka ColemanSolar responded within a working day, OTOH Coleman Canada took 6 weeks to reply to a different online query.

IOW, I've put my rewire on hold till it comes out and I can figure out how to fit it into my system. I understand the solar part, but not sure how my Tow Vehicles 12V connection or the separate 120V charger will all fit in. I'm not sure what the cost will be, but if you consider the 3 panel Coleman Solar kit retails for $300 CDN, I don't expect the controller will be very expensive.
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Old 10-05-2007, 03:57 PM   #4
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Name: DK
Trailer: 2006 Escape
Posts: 19
There are circuits out there that use MOSFETS to do the switching which would eliminate the current-eating relay coil. As well, there are circuits that will allow the relay coil, if used, to be actuated and then drop the voltage off to a point that will just barely allow the coil to stay energized thus reducing the current draw as well.

I am definitely interested in exploring these options because it would be a great help to the battery. On the other hand, I also don't want to shoot myself in the foot by using up the very power I'm trying to conserve.

Hopefully we will receive more posts on this topic from some who are more familiar with the concept.
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Old 10-06-2007, 12:30 PM   #5
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Trailer: 2006 17 ft Casita Spirit Deluxe
Posts: 139

I use a battery disconect in my teardrop trailer. Be careful how low you take you battery, though. 12.24 (open circuit) is a 50% charge and if you always recharge it at that point, it will double the life of the battery. 11.89 (open circuit) is 0% charge!!!!!
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Old 10-06-2007, 12:40 PM   #6
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Name: Per
Trailer: 2000 Burro 17 ft Widebody towed by Touareg TDI
Posts: 863
It occurs to me that the Open Circuit readings need another qualifier: time to reach the correct reading. Somehow I recollect that taking a voltage reading immediately after disconnecting everything does not give a true reading. Several hours, maybe even overnight might be needed for the open voltage to be stabilized. It seems that the tables for these things need that added to them. Anyone have good info on this?
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Old 10-06-2007, 05:36 PM   #7
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Trailer: 2006 16 ft Casita Spirit Deluxe
Posts: 24
Hi, all - there was a thread today on Casitaclub.com with a great chart showing both open & loaded battery levels. Don't have the exact link but should be easy to find.

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