Auto Battery Load Disconnect

[dustinp]

Thx dustin! I just realized I need to do this as well.

Hey grasshopper.
I used a multi-meter to find a fuse that was powered only when the ignition was on, but since there wasn't an empty fuse position with that characteristic, I used an adapter https://www.amazon.com/gp/product/B013JXVG2U/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 to add a second fused circuit to one that was already there. It allows you to put the original fuse in the adapter, and add a second one for powering the relay https://www.amazon.com/gp/product/B00C0SATHE/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
In the attached pic you can see the red wire coming out of the adapter in the fuse block to the right and going to power the relay. In the lower left corner you can see where I pulled the hitch power from the lug at the front of the fuse block with a red fused #8 wire that wraps around the back of the fuse block and attaches to the yellow input wire of the replay, and exits the relay as the heavy blue wire that is routed back to the hitch. That's now a 6 yr old installation, so things are a little dusty compared to when installed. The wires are all usually pretty much invisible when tucked in behind the fuse block with it's cover on, with the relay tucked along the back side, but I pulled them all up to take the pic.View attachment upload_2022-9-9_9-37-46.png

 

[dustinp]

Thanks Dustin! This is what I needed!

Your welcome! Always like to help a fellow camper...God knows I've received more than my share of help from this forum.

 

[dustinp]

Мы все здесь, чтобы помочь нашему ближнему

I said no such thing, but then I think you've been hacked

 

[Sweeney]

Oddly, a polite and friendly spammer

 

[dustinp]

I added a switch to the wiring harness this afternoon, which allows me to turn off the onboard battery charger if I want to plug the TD into the sogen for AC power, without using its power for recharging a partially discharged TD battery.
The low voltage monitor/ disconnect should keep the TD battery from discharging to the level of damage, then the switch should give the sogen the longest usable life until recharge power is available.

 

[gregangsten]

Thanks for your reply rmbrowder!
I checked out the info in the Dometic operating manual and from what I found, it sounds like the cutoff voltage even when set on high will cut off the current to the fridge at a voltage(11.8V) that corresponds with what is considered a very deep discharge, well below 50% of capacity (actually at about 30%).
From what I've been reading it sounds like 50% is the maximum depth of discharge (DOD) a deep cycle battery should be taken down to before damage to it's charge capacity will begin to occur. The Lithium Iron Phosphate batteries can safely be taken down that low and lower, but it doesn't sound like any of the lead acid batteries should.

When setting the voltage cut-off level on the refrigerator, keep in mind that there is a temporary voltage drop each time the compressor switches on. It quickly returns to a higher equilibrium voltage as it runs but if you have set this at a higher V level to cut off it will likely shut down earlier than it needs to. You might monitor the V as it switches on to verify this and to determine what setting you should use.

 

[dustinp]

I added a switch to the wiring harness this afternoon, which allows me to turn off the onboard battery charger if I want to plug the TD into the sogen for AC power, without using its power for recharging a partially discharged TD battery.
The low voltage monitor/ disconnect should keep the TD battery from discharging to the level of damage, then the switch should give the sogen the longest usable life until recharge power is available.

I added the second part of the TD battery bypass when using a sogen to backup a depleted TD battery. You can leave the TDs battery disconnect in the off position then plug a double ended cigarette plug cord into the kitchen 12V outlet. That will allow the sogen to power your 12V system, lights,fan,etc., but not send current to the depleted battery, thus increasing the sogens longevity.

I've' replaced all of the cabin lights with LED's, so don't think this should put too much voltage thru the receptacle or plug, but I haven't totaled what the current would be if all the 12V system components were being used at the same time, so before using this method you may want to figure that out, or use them sparingly if using this idea. So use at your own risk.

 

[dustinp]

When setting the voltage cut-off level on the refrigerator, keep in mind that there is a temporary voltage drop each time the compressor switches on. It quickly returns to a higher equilibrium voltage as it runs but if you have set this at a higher V level to cut off it will likely shut down earlier than it needs to. You might monitor the V as it switches on to verify this and to determine what setting you should use.

Good observation, but unless you are using a lithium battery that can be more deeply discharged, even the higher voltage cutoff point of 11.8V (which is about 70% discharged) happens when the lead acid battery has already been harmed (more than 50%), so I wouldn't count on that shutdown feature on the fridge to save you from damaging the standard lead acid TD battery. On the other hand, if you have a lithium battery, you could probably get by using the medium(11.4V) setting, but the low (10.1V) might even harm the lithium battery.