Power Management with Fridge

[carbon60]

My 37-qt ARB fridge/freezer should arrive tomorrow! :wings:

Now, on a trip where I intend to be stationary for about 3 full days, how should I manage my battery?

1. I have a single Norstar (read Odyssey) AGM as my starting battery;
2. I carry a fully charged spare battery (not connected);
3. 1996 80-series LC with a hand throttle;
4. The forecast is for sun and a high of 25ºC;

So, should I run the engine for an hour after being parked for 48? Is it more efficient to run at idle or some higher RPM, in order to charge the battery?

Maybe I should set the voltage cut-off on the ARB to "high", but then I have no way of alerting myself that the fridge thinks I should recharge.

Comments, ideas, suggestions?

Thanks,

A.

 

[Hilldweller]

You're running the fridge off the RedTop?
They're starting batteries and don't take kindly to any sort of deep cycling.
I'd start thinking about some sort of solar or something to keep the battery fully charged.

 

[carbon60]

You're running the fridge off the RedTop?
They're starting batteries and don't take kindly to any sort of deep cycling.

I'm running a Norstar AGM, which is basically an Odyssey, and doesn't mind deep cycling at all.

Looking for the short-term solution, here. Long term I will get a dual-battery system installed and a solar panel to help it along.

Thanks,

A.

 

[Stumpalump]

Plug it in at the house days before and set it cold. Put frozen water bottles in it take your girlfriends car battery as a third.

 

[AndrewP]

I doubt you'll have much of a problem, but the spare charged battery is a good idea.

Some obvious tips:
Get it cold with everything in it before you go-using house power
Keep it out of direct sun-covered in a reflective windshield screen works great (the cheap ones from the auto store)
When parked, keep in the shade if possible and keep the windows open so your inside ambient doesn't spike
Take a voltage tester and test your battery a couple of times a day -if you drop below about 12.1, you will want to run and recharge
1000rpm is a good charge speed

You could also take one of those battery booster packs to jump with if you're worried.

 

[goodtimes]

My ARB fridge (50qt) will run for about 2 days on a single Odyssey battery with no external help (solar, running the engine, etc). This was not my starting battery, so running it down wasn't a huge concern.

To keep it charged, I would run the engine for 15 - 20 minutes per day, which worked out OK, other than the noise & smell (diesel) in camp.

Given that you carry a fully charged 2nd battery, I'd suggest you run the fridge off of that rather than your starting battery. Just recharge it every day or so (jumper cables to your starting battery with the engine running for 20 minutes or so). That removes the risk of running your starting battery down with minimal added cost (you already have the battery & probably have the cables too).

 

[carbon60]

Take a voltage tester and test your battery a couple of times a day -if you drop below about 12.1, you will want to run and recharge
1000rpm is a good charge speed

Thanks, I'll do exactly that.

Given that you carry a fully charged 2nd battery, I'd suggest you run the fridge off of that rather than your starting battery. Just recharge it every day or so (jumper cables to your starting battery with the engine running for 20 minutes or so). That removes the risk of running your starting battery down with minimal added cost (you already have the battery & probably have the cables too).

That's an option which, as you point out, I'm already equipped for.

Thanks for the input!

A.

 

[Hilldweller]

You're not doing your alternator any good by trying to charge a deeply discharged battery, even in parallel with the starting battery.
I thrashed a big Sears DieHard Platinum that way.
The battery and alternator will like it best if you recharge all the way every day.

Which Northstar do you have?

 

[carbon60]

You're not doing your alternator any good by trying to charge a deeply discharged battery, even in parallel with the starting battery.
I thrashed a big Sears DieHard Platinum that way.
The battery and alternator will like it best if you recharge all the way every day.

ARB's controller should turn the fridge off at 11.8V:

That seems rather extremely low for their "high" setting. Unless my understanding of batteries is way off.

So, should running the engine for 20 minutes at 1000 RPM fully recharge the battery?

Which Northstar do you have?

NSB-AGM-35

Thanks,

A.

 

[carbon60]

That seems rather extremely low for their "high" setting. Unless my understanding of batteries is way off.

Found the NorthStar State of Charge chart:

 

[AndrewP]

So, should running the engine for 20 minutes at 1000 RPM fully recharge the battery?

.

Let's say you have an 80 amp.hour battery that's half discharged.

Let's also assume that your alternator is good and can generate the spec 80 amps.

So 80amps for 30min (0.5 hour) would in a perfect world put 40 amp.hours back into your battery and thus fully charge it. Now obvioulsy the situation is less than perfect and it's unlikely it will be generating 80 amps, and even less likely your battery can accept charge at that rate, but it gives you the idea.

I know my 80 starts reliably at 12.1v, and so I monitor and when close to that, simply run or drive a bit to charge it up. If you have a Yaesu radio, it reads voltage when you power up the radio, and so often I'll turn the radio on, read the battery voltage and shut it back off. You don't even need to open the hood.

The only time I've had any issue at all, was running 2 refrigerators, and was in Death Valley where there was no shade. After 24 hours the truck barely turned over, but did in fact start. Your spare charged battery is a poor man's dual battery and will take away any worries you may have.

 

[Hilldweller]

11.8v is extremely low for that battery ---- and it's going to be bouncing there violently as the compressor kicks on, the shut-off occurs, the battery recovers, the compressor kicks back on, etc.
As the battery ages, the compressor load will drop the voltage more and more violently. It will be about .3 volts at first, then .5v, then 1v, and so on.

 

[Mike S]

I turn my fridge off at night. Ambient air temp is lower, and you will not be opening and closing it when you are asleep. Turn it back on first thing in the AM.

On long trips, I have left my Engel 45 on constantly when using it as a freezer - it never discharged my truck batteries any noticeable amount, even when parked for several days. This was over a period of more than a month.

 

[4x4junkie]

ARB's controller should turn the fridge off at 11.8V:

That seems rather extremely low for their "high" setting. Unless my understanding of batteries is way off.

It could be they are accounting for a bit of voltage drop in whatever wiring is being used (even the best installations can often experience around 0.25 volt loss by the time the power reaches the fridge's compressor controller). Most any battery's voltage will also "rebound" a little bit after the fridge cuts off... In other words, if the fridge is set to turn off at 11.8V, and your wiring has a loss of ¼ volt, the battery will actually be at 12.05V when it cuts off, from which it may 'rebound' to something around 12.3V which would be approx 50% SoC.
Setting it to MED under those same conditions would leave the battery hovering somewhere around 20% SoC.
Unless your wiring is very lossy (plugged into the average vehicle's cigarette-lighter socket, etc.), there should be no reason whatsoever to use the LOW setting.

 

[carbon60]

It could be they are accounting for a bit of voltage drop in whatever wiring is being used (even the best installations can often experience around 0.25 volt loss by the time the power reaches the fridge's compressor controller). Most any battery's voltage will also "rebound" a little bit after the fridge cuts off... In other words, if the fridge is set to turn off at 11.8V, and your wiring has a loss of ¼ volt, the battery will actually be at 12.05V when it cuts off, from which it may 'rebound' to something around 12.3V which would be approx 50% SoC.
Setting it to MED under those same conditions would leave the battery hovering somewhere around 20% SoC.

That makes a lot of sense, I will measure voltage in a couple of spots, today.

I actually received the fridge Friday, about 10 minutes after I was too far along my long-weekend route for it to be worthwhile turning back. But I should be able to test everything this weekend.

Thanks for the input!

A.