Protecting your battery with a low voltage disconnect

[motorbreath]

I have been learning the "hard way" about batteries for my TT. After killing the second one because of mistakenly putting a manual disconnect on the positive terminal, I have been reading to avoid more silly mistakes. There are tons of discussions about which batteries are best, 6v series be 12v, solar, generators, you name it...but I cannot find one about low voltage disconnects.

A low voltage disconnect automatically disconnects your battery once a certain minimum voltage is reached, protecting it from being completely discharged. Most battery management systems for solar setups have these built-in...but everyone can use them. I have found them online for around $100 and installation is super simple.

Why aren't people using them, am I missing something? Here is an example of a barebones low voltage disconnect

http://www.digikey.ca/en/product-hig...age-disconnect

[bansai]

Looks like an option for sure. Possibly people are concerned about disconnecting a critical item that they would rather see drain their battery than cause even more problems. I don't have a CPAP machine, but that's one thing that comes to mind. Sometimes it's better to toast a battery than stop breathing

That said, I'm also surprised I haven't seen anyone talk about these cut offs before. I watch my battery like a hawk and haven't gone below 12 volts yet, but I know a lot of people (add you to the list ) that have. I take a minimalist approach myself and don't anticipate installing anything like that. It looks like it also adds a small amount of additional parasitic drain to the system if I'm reading the spec correctly and 150 bucks seems a little high to me? I'm always looking at cost benefit. I guess if I had fried 2 batteries, I'd easily justify it.

I'd prefer something like this at half the price, since my battery is fully disconnected when I'm not camping

http://so-bfd.com/
Basically it's a user configurable low voltage alarm. If I had the resources (money) I would install an auto start generator in combination with low voltage monitoring, but that starts to blow away my 'keep it simple' philosophy.

Edit to add - before installing my battery disconnect, I read up on it and installed it on the negative terminal by default as best practice, but I don't understand how installing it on the positive side would allow your battery to discharge. I thought you put it on the negative side for safety reasons, no other reason.

[eldermike]

I would rather use a low voltage cutoff on a system not on the battery.

[lx22f/c]

I have installed a low voltage disconnect on a car that had a draw on battery.
Vehicle needed a expensive body control module (which would have exceeded car value) we installed a auto disconnect and that solved his problem. It would disconnect when battery voltage hit 11.8 volts. To reset all you had to do was turn on head lights and off and it would give you battery voltage again.



Sent from my iPhone using Tapatalk

[motorbreath]

I can imagine that if you have a CPAP or other mission-critical device you would prefer to sacrifice your batteries...but I cannot imagine people with this need boondocking very often because of the risks.

Price is definitely an issue, but a company called Blue Seas makes a much more affordable and functional one, search Amazon for "Blue Sea Systems m-LVD Low Voltage Disconnect", they are currently on sale for $50 (so I bought one!).

Regarding the negative terminal being so important, I am not exactly sure why but your battery will definitely drain if you leave it connected and disconnect the positive side.

Originally Posted by bansai

Edit to add - before installing my battery disconnect, I read up on it and installed it on the negative terminal by default as best practice, but I don't understand how installing it on the positive side would allow your battery to discharge. I thought you put it on the negative side for safety reasons, no other reason.

[M&A]

Originally Posted by motorbreath

I can imagine that if you have a CPAP or other mission-critical device you would prefer to sacrifice your batteries...but I cannot imagine people with this need boondocking very often because of the risks.

Price is definitely an issue, but a company called Blue Seas makes a much more affordable and functional one, search Amazon for "Blue Sea Systems m-LVD Low Voltage Disconnect", they are currently on sale for $50 (so I bought one!).

Regarding the negative terminal being so important, I am not exactly sure why but your battery will definitely drain if you leave it connected and disconnect the positive side.

Can't see how the battery would drain. Only reason to use the negative terminal is so that the disconnect switch won't have an easy to short to ground if mounted on the frame.

Curious about an automatic disconnect - if the battery gets to a point where LVC will drop, how will the charger (on-board converter) charge it when plugged in?

[motorbreath]

My understanding is that it automatically reconnects, the Blue Seas kit also comes with a manual override switch as well. From their website,

"The m-LVD will will reconnect when voltage is above 13.0V for 2 minutes or 13.5V for 30 seconds."

Originally Posted by M&A

Curious about an automatic disconnect - if the battery gets to a point where LVC will drop, how will the charger (on-board converter) charge it when plugged in?

[troutslayer]

Originally Posted by motorbreath

Most battery management systems for solar setups have these built-in...but everyone can use them. I have found them online for around $100 and installation is super simple.

Did you mean NOT everyone can use them? Because my take would be to add about $200 more and set up a solar charger for the battery. Then you don't have to be concerned about it. Sorta like killing two birds with one stone, so to speak.

[motorbreath]

I found one much cheaper, $50 shipped, see post above. I think a true battery management system would also be a good idea, as you say, but cost is definitely higher and installing it more complicated.

Since you brought it up, how complicated is it to bypass or remove the factory charger and install your own?

Originally Posted by troutslayer

Did you mean NOT everyone can use them? Because my take would be to add about $200 more and set up a solar charger for the battery. Then you don't have to be concerned about it. Sorta like killing two birds with one stone, so to speak.

[motorbreath]

After waaaay too much time spent researching this topic, I do not think having a solar charger is adequate. Initially, my only understanding of solar power systems is for home systems, which all have logic to protect house battery banks which can be $10-20k or even more in value. RV solar power systems seem to be more simple, I was not able to find one that has built-in low voltage protection for the battery.

Correct me if I am wrong, but an RV solar power system is added-on to an existing converter/charger that comes with your RV, or maybe upgraded to an inverter/charger. All of the wiring diagrams I have seen have the battery, solar charge controller, converter/ charge controller, and DC loads (water pump, lights, etc) on the same circuit in parallel. There is no central battery management system like in home solar power systems which manages all of these things using separate circuits.

I think a low voltage disconnect is especially important for RV solar systems since you likely invested some serious $$$ in quality deep cycle batteries. Unless you have an integrated generator which kicks-in when the voltage becomes too low, it is a good $50-100 investment.

Originally Posted by troutslayer

Did you mean NOT everyone can use them? Because my take would be to add about $200 more and set up a solar charger for the battery. Then you don't have to be concerned about it. Sorta like killing two birds with one stone, so to speak.

[RoyBraddy]

Blue Sea products have just what you are looking for like talked about above...

m-LVD Low Voltage Disconnect Smart relay model 7635


Google Image

Check this out on-line and see if it will fit your disconnect requirements. I believe you can set the SMART RELAY to trip off on a wide range DC Voltage setting...

Check with BLUE SEA for the drawings and specs and you can purchase this from AMAZON

Roy Ken

[motorbreath]

Thanks, ordered one last night from Amazon, on sale for $50 delivered!

Originally Posted by RoyBraddy

Blue Sea products have just what you are looking for like talked about above...

m-LVD Low Voltage Disconnect Smart relay model 7635


Google Image

Check this out on-line and see if it will fit your disconnect requirements. I believe you can set the SMART RELAY to trip off on a wide range DC Voltage setting...

Check with BLUE SEA for the drawings and specs and you can purchase this from AMAZON

Roy Ken

[Mustang65]

Just a reminder that the relay uses .09Amps/Hr so it will add up if you are not going to be checking the battery on a regular basis. It adds up to 2.1Ah each day or 15 Ah each week that the relay is activated. It can still run your battery down.

Don

[troutslayer]

Originally Posted by motorbreath

After waaaay too much time spent researching this topic, I do not think having a solar charger is adequate. Initially, my only understanding of solar power systems is for home systems, which all have logic to protect house battery banks which can be $10-20k or even more in value. RV solar power systems seem to be more simple, I was not able to find one that has built-in low voltage protection for the battery.

Correct me if I am wrong, but an RV solar power system is added-on to an existing converter/charger that comes with your RV, or maybe upgraded to an inverter/charger. All of the wiring diagrams I have seen have the battery, solar charge controller, converter/ charge controller, and DC loads (water pump, lights, etc) on the same circuit in parallel. There is no central battery management system like in home solar power systems which manages all of these things using separate circuits.

I think a low voltage disconnect is especially important for RV solar systems since you likely invested some serious $$$ in quality deep cycle batteries. Unless you have an integrated generator which kicks-in when the voltage becomes too low, it is a good $50-100 investment.

I dunno...you may be over thinking this??? For me, I store my RV outdoors and have a solar set up and a true deep cycle AGM battery so I never worry about the battery running below 50%. Now, when I am boondocking and strictly on battery power, I use a battery monitor (very inexpensive) to keep an eye on the battery level. If it gets around the 50% level, I would start shutting stuff down. I say "would start shutting stuff down" because its never happened. I have an inverter generator but have not used it since installing the solar set up. I bought the Renogy system...not saying its the best but it was a simple set up. Is Mustang65 anywhere around? He can give you very good advice on solar systems.
Good luck!

[RoyBraddy]

Originally Posted by motorbreath

Thanks, ordered one last night from Amazon, on sale for $50 delivered!

Will be curious how this is going to work for you... I am interested in doing something similar here. I will have a simple solar hookup to trickle charge things between Battery checks here...

As Mustang65 commented just running the Low Battery Alarm circuits eats up battery power as well... My simple solar hookup here should be enough to overcome that small drain...

After reading up on the Blue Sea Low battery Alarm I still like what it would do for my recent battery bank changes I am working on and will incorporate something like this to work for my setup...

Just about all of my 12V Battery DC Projects use BLUE SEA Marine Products and glad to be able to order those thru AMAZON and get the 2- day delivery on them...

[pop up pilot]

I was considering the low voltage disconnect just to protect my battery. I looked at one rated for 30 amps. So, if I had my heater on at night, and the battery hit my selected safe voltage, the battery would be saved. However, I was wondering if it has a diode that would prevent the internal charger from charging the battery. The LVD has a line and a load side. What happens when voltage from the charger is applied to the load side? If all else fails, I could wire the LVD into the heater circuit, that way it only cuts off the large load of the heater if the battery is at risk. Also, does anyone have any references on why to disconnect the negative terminal? I am OK with that advice, I just like to have a full understanding of my system.

[Mustang65]

Originally Posted by pop up pilot

Also, does anyone have any references on why to disconnect the negative terminal? I am OK with that advice, I just like to have a full understanding of my system.

Looking at how the TT's are wired the primary reason for installing the Battery Cut-Off Switch on the NEGATIVE (Ground) side of the battery system, would be for a VERY easy installation. Most cut off switches are the marine Blue Sea type of switches. They can be mounted directly to the TT's frame right next to the TT's existing frame's grounding point. Usually a bolt that is tapped directly into the frame. The battery cut off switches have cutouts so connecting the cables is effortless.

All you need to buy is the Marine Cut-off Switch and go to an automotive store and purchase a BLACK 6" battery cable with a lug for a bolt on each end.
- Before installing the switch, turn it to the OFF position
- Disconnect the existing GROUND cable (should be white) from the frame ground connection bolt. There may be a few other wires connected to that bolt also.
- Connect the new 6" BLACK battery cable to the Marine cut-off switch.
- Connect the other end of the new 6" battery cable to the frame grounding bolt and tighten the bolt back into the frame (along with any other wires that were originally on that connection).
- Mount the Marine cut-off switch to the frame
- Connect the WHITE cable from the batteries NEGATIVE terminal to the other side of the Marine cut-off switch.

Total installation time is less than a half hour.

This is an easy installation for a regular TT's wiring. If you have an a large inverter then that will require a little different wiring.

Don
-

[bansai]

Other than the safety reasons for disconnecting the negative terminal, which I could get into and provide references for, the actual terminals on the battery are different sizes between - and +. If you were to try to install the cutoff I'm using on the positive post, you're going to damage something.. either the post, or the cutoff switch connector...

This is what I went with, super cheap, works great. Top Post Battery Master Disconnect Switch

[Mustang65]

If you feel ambitious, why not assemble your own automatic cutoff switch for $18. It is a 30Amp switch. Uses 2 mA, has adjustable CUTOFF voltages at 12.1V, 11.4V, 10.7 or 10.0 and an adjustable RECONNECT at 12.8, 12.1, 11.4, 10.7 volts . Needless to say the best cutoff voltage would be 12.1.

The drain of .002Amps * 24hours=.048Ah each day (not bad!!), the operating supply voltage is between 3VDC and 18VDC.

This would be a good project... purchase a small project box, mount the automatic cutoff module in the box, purchase a chassis mounted BLADE fuse assembly and mount it on the outside of the box, use the TT's battery cable that has the inline main 30 amp fuse in it. Seal the project box to protect it from rain/snow. Then mount it to the frame or battery box.

You could be building this a home during the winter months for something to do.

As with any automatic cutoff switch an initial high amp surge may drop the voltage for any automatic cutoff switch below the lower voltage set point. Not sure if there is a timer that allows this for so many seconds without disconnecting.

Just a thought,

My Registry

Don