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Old 04-12-2016, 12:27 PM   #1
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Low Voltage Disconnect - Where to integrate?

I recently had an experience where I thought my batteries were being charged while I was gone but the breaker from the utility power connection tripped and my batteries completely discharged (well, down to 6-7 volts). I'd like to prevent this happening again and I think integrating a "Low Voltage Disconnect" switch will go a long way toward accomplishing that goal.

I guess my basic question is where I should integrate a low voltage disconnect in my electrical configuration...

Right now, I have the following components attached directly to the positive post of my battery bank:
  1. Inverter/Charger (fuse and disconnect switch between it and the battery bank)
  2. 12v Panel (breaker and disconnect switch between it and the battery bank)
  3. Tow Vehicle Charge Line (breaker and disconnect switch between it and the battery bank)
  4. Victron Battery Monitor (fused between it and the battery bank)
  5. Battery Compartment Exhaust Fan (only on during charging, fuse between it and the battery bank)

Since I have these 5 things attached directly to the positive post of the bank, I guess I'd need ALL of them to go to the Low Voltage Disconnect instead. Or maybe have these all go to a common 12v+ "bus bar" which would be connected to the Low Voltage Disconnect.

Or would you want to leave some of these 5 things attached directly to the battery bank?

Maybe keep the inverter/charger connected directly to the bank so that in the situation I described above if shore power miraculously became available again the charger would turn on and begin re-charging the batteries? (Inverter has its' own built-in low-voltage DC disconnect)

BTW, thinking this low voltage disconnect unit would work:

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Blue Sea Systems 7635 m-LVD Low Voltage Disconnect

Diagram of my electrical setup:

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Old 04-12-2016, 03:10 PM   #2
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I'm a newbie and the subject is very interesting to me. Following your link, the disconnect will reconnect when it senses 13v for 2 minutes or 13.5v for 30 seconds. I read that in the FAQs.

Adjustable disconnect voltage.....nice.
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Old 04-12-2016, 03:21 PM   #3
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Main positive battery cable as a master disconnect.


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Old 04-12-2016, 03:53 PM   #4
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Quote:
Originally Posted by lewster View Post
Main positive battery cable as a master disconnect.
Is there a Main Disconnect Switch that you like/prefer? Or are you saying to actually / physically disconnect the cable from the battery?
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Old 04-12-2016, 04:14 PM   #5
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If you want a real positive disconnect look to something like this.

http://www.summitracing.com/parts/mo...FQckhgodt2QAkQ

I think I would first find out why the breaker tripped in the first place. The convertor should not draw that kind of power. The breaker may be week, it happens
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Old 04-12-2016, 05:28 PM   #6
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Quote:
Originally Posted by HowieE View Post
If you want a real positive disconnect look to something like this.

http://www.summitracing.com/parts/mo...FQckhgodt2QAkQ

I think I would first find out why the breaker tripped in the first place. The convertor should not draw that kind of power. The breaker may be week, it happens

It was the breaker at the utility breaker box, not the breaker inside the airstream. There must've been a power surge or something on the utility side that popped the breaker
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Old 04-12-2016, 05:37 PM   #7
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I noticed your diagram doesn't include a Use/Store switch and battery disconnect relay like the modern trailers. Instead of adding a low-voltage monitor, why not consider a Use/Store switch, so you can be assured that when you leave your trailer, by selecting one switch near the door, nothing will drain down your batteries?
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Old 04-12-2016, 07:10 PM   #8
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Quote:
Originally Posted by MarkR View Post
Is there a Main Disconnect Switch that you like/prefer? Or are you saying to actually / physically disconnect the cable from the battery?
I prefer the manual type like the Blue Sea Systems M-Series: https://www.bluesea.com/products/600...th__Knob_-_Red
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Old 04-13-2016, 08:43 AM   #9
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Before spending money on a switch check the breaker that opened. There had to be a reason for it opening. That is most likely an over draw of current or a weak breaker. What else may be on that circuit? As for a power surges they are an urban myth used to sell useless devices to the RV community. Short of a lighting strike, and the device most likely would not protect against one, a surge is unlikely.
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Old 04-13-2016, 04:34 PM   #10
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I had a 50 Amp. pedistal ground wire come loose. The 230 volt surge caused me to replace all AC and DC units that were on at the time. Fortunately, my insurance company paid the bill. I now own the most elaborate and expensive surge protector money can buy. It is the only device that can automatically take care of or prevent surge damage besides my insurance company. When in doubt, check the source, and either don't connect or disconnect which ever is appropriate.
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Old 04-13-2016, 06:01 PM   #11
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Low Voltage Disconnect - Where to integrate?

Surge protection alone is not sufficient. Power protection also needs to include under volt, over-volt and polarity checks.

It's NOT an 'urban myth'. Better than half my engineering career was designing lab power systems that provided clean power, good grounds, and protected rather pricy hardware from power faults. A decent power protection system is cheap, compared to the hardware it protects. Our AS, before I got it, burned out an air conditioner due to undetected low voltage. Insurance covered the replacement, but believe me,loosing A/C in Texas in the summer was not just simply inconvenient...


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Old 04-14-2016, 08:02 AM   #12
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Quote:
Originally Posted by rmkrum View Post
Surge protection alone is not sufficient. Power protection also needs to include under volt, over-volt and polarity checks.
I agree. I have the Progressive Industries EMS-HW30C installed.
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Old 04-14-2016, 08:22 AM   #13
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Quote:
Originally Posted by alano View Post
I noticed your diagram doesn't include a Use/Store switch and battery disconnect relay like the modern trailers. Instead of adding a low-voltage monitor, why not consider a Use/Store switch, so you can be assured that when you leave your trailer, by selecting one switch near the door, nothing will drain down your batteries?
Thanks for taking a look at the diagram!

That's not a bad idea... My original strategy was to have individual battery disconnect switches for each major system connected to the battery bank (inverter, charger, 12v panel, etc...) and leave some items I wouldn't want to turn off with any of those major systems connected directly (well, via a fuse) to the battery bank.

Help me understand the "use/store" use-case a little better... In my case, I'm in Michigan, so "storing" my Airstream means putting it in an unheated barn for the winter and making sure Shore/Utility Power is connected to the AS to keep the built-in charger charging the batteries all winter. In that case, I would NOT want a "use/store" switch to disconnect the batteries because that would mean no charging and subsequent freezing of the batteries.

Is a "use/store" switch more for short term "storing" where you don't need to have a charger running? In my case, my charger is a combo unit Inverter/Charger/Transfer-Switch, so I don't think it makes sense to have it installed "behind" a "use/store" switch (which would be one method to allow charging even when "use/store" switch is in the "store" position).

Any insight?
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Old 04-14-2016, 08:31 AM   #14
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Quote:
Originally Posted by lewster View Post
Main positive battery cable as a master disconnect.
Lewster, if I'm interpreting your response correctly, instead of an automatic low-voltage disconnect switch you are advocating a "master" battery disconnect switch (complete disconnect of everything from positive post of battery bank). Is that correct?

If my interpretation is correct, I don't understand how that would help my situation... I am looking for a method of automatically disconnecting the batteries when they get too low when I'm not around to monitor the situation myself. My recent experience was one in which I intended to keep the AS 12v system on and operable while I was gone (for the guys working on the trailer), not one in which I accidentally left everything on and the batteries were subsequently drained. I can understand the "master" disconnect strategy if I intended for the AS electrical systems to NOT be used when I was away, but in this case I needed them to be operable when I was away and am looking for a way strategy that would prevent the batteries from being drained if shore/utility power becomes unavailable during that time.

Penny for your thoughts?
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