Critical Voltage Levels?

I just installed a SeeLevel tank monitoring system that includes a nice battery voltage reading as well as the tank levels. I am on our first trip since installation. Much better than the old original full-2/3-1/3-mt monitoring system. And I'm using a chart of unloaded voltage vs. relative capacity to keep track of how much battery I've got left.

Are there critical voltage levels for the HiLos that I should be aware of. Specifically, I wonder about what voltage the hydraulic pump system needs since I know it is a big battery power user when operated. But there may be other systems that need critical voltages as well. How about the water pump, or the control systems on the refrigerator or water heater?

Anyone have any info on critical voltage levels for these different systems?

"Critical" voltage would be the nominal voltage of the given battery type, regarldess of the system using it.

A 12v battery (from memory, and I'm bad at math) should, nominally, output 2.1v per cell. Since there are 6 cells, that comes out to 2.1*6=12.6v

Or is that 2.2v*6=13.2?

Crap, my memory sucks.

Anyway, you should see above 12.5v at the battery, with no load/nothing connected.

That's a minimal test - even a bad battery can output 12+ volts, and still not deliver enough current to operate anything. So don't think just cause you have voltage everything is hunky-dory.

Knotty,

I guess I should have been more clear in my request for info. I am looking for any minimum voltage levels that the user systems need. If anything in the normal range of a 12v battery is OK, then great. That would make it simple and I only need to worry about how much battery capacity is left.

Knotty, your first recollection was correct. A fully charged new battery in the "resting state" under no load should read 12.7V. So, each cell delivers just a bit over 2.1V.
I believe 12.5V is an 80% charge state.

Camper, it's a bit difficult to guess the minimum charge state that would raise the top. I actually had it work after driving all day, with the refrigerator running off DC power and the tow vehicle charging fuse blown. I suspect it was down to about 1/4 remaining. As I remember, the motor ran slowly, but it DID lift the top all the way.

If you are "dry camping", you should run the water heater and refrigerator on propane. They will operate much more efficiently that way and you save your battery. The water pump pulls a bit over 2 Amps as I recall, but it will run with fairly low voltage. Fortunately, it doesn't have to run for very long each time it's used.

If you're planning to do a lot of dry camping, I suggest you buy an inverter generator. They are available online or at stores such as Costco and Home Depot and they are not horribly expensive or noisy. They also run for several hours on a tank of gas, maybe about 1/4 - 1/3 of a gallon?

- Jack

Thanks for clarifying Jack- I always have to look this stuff up because I operate from general rules rather than try to push to the limits.

To that end, isn't any level under that 12.5v considered low?

Camper- are you looking for what minimum voltage level will drive a given system? If so, thats not a great approach- as you drop to those minimum voltages, current draw (and heating) increase, which is just a Bad Thing.

KnottyRig said:

...<snip>...
To that end, isn't any level under that 12.5v considered low?

Camper- are you looking for what minimum voltage level will drive a given system? If so, thats not a great approach- as you drop to those minimum voltages, current draw (and heating) increase, which is just a Bad Thing.

Click to expand...

Yes, Knotty. If you drop below 12.5V the battery should be recharged as soon as possible to prevent the damage that actual "deep cycling" causes.

And, your advice to Camper is DEAD RIGHT! If the voltage drops, the Amperage has to increase to supply the needed Wattage. This all drains the battery even faster and it causes damage to the components that are being powered.

- Jack

Thanks for the advice everyone! Sounds like the power draw from the hydraulic lift system is the limiting one. Also sounds like I should play it conservatively with the voltage levels since that amperage draw is so high. My 12v deep cycle battery table shows a 50% discharge no load voltage of 12.1, so maybe 12.3 for a first operational limit. I'll test how the hydraulic system does at 12.3 (and if the battery stays above 12.1) while I'm at home just to be safe. I have already learned that with my parallel battery system the battery that the hydraulic system is directly connected to should be kept fresh for last.

How's your parallel battery system setup? Are you able to take one battery out of the loop when energizing different systems?

If not, then both batteries will always be energizing systems together, with nearly equal current draw from both (with differences due to cabling and battery condition).

Knotty,
I have a couple of heavy duty switches set up so I can use or charge each battery separately or together. When dry camping, I typically have only one on line at a time. I have a 100 watt solar panel which helps to recharge the on-line battery during the day, but the battery will slowly lose ground over each day-night cycle.
So when I reach my drawdown limit (12.1v on the first one), I'll switch to the second one (connected at the terminal to the hydraulic pump) until it gets down to 12.3v. That assumes my at-home testing shows that 12.3v is enough to drive the hydraulic pump and not drain the battery below 12.1v.