Trying to set up my Cherokee to run a fridge off solar.

[65BAJA]

I have a older 40qt ARB fridge that I carry in my Jeep Cherokee. I have always had problems keeping a battery charged. I started out running it off the starter battery(red top Optima). Yea, that didn't work out so well. So I added a 2nd Optima, a yellow top. It was better but I was still killing the battery and could not go a full weekend on a charge. Then I added two 18W polycrystalline solar cells. That helped quite a bit. But I still could not go a full weekend.

Recently I decided to do some serious upgrading. I now have 2 G31 Blue top Optima batteries, two 160W Grape Solar Monocrystalline solar panels, and a GS 320W MPPT controller. After buying all this I found this place and started reading. I see there are a few ways I could put this system together and some more equipment I might want to add. I keep reading about shunts and battery monitors. I'm wondering if I need one of these because the charge controller I have tells me how many amps it's putting into the batteries and how many volts the batteries are currently reading. It also shows how many amps the connected load is drawing.

I would like a system that can run the fridge indefinitely, and still be able to run a HAM radio intermittently. Do I have enough watts? Battery capacity? Do I need a monitor?

 

[Howard70]

Hello 65Baja:

Short answer - you should be fine, and you only need a monitor if you want to know what's going on in detail (some of us obsess over that!). It sounds like you'll have 320 watts of solar with about 200 amp hours of storage. I'd recommend connecting the two batteries in parallel to get the effect of one big battery (lots of technical reasons for doing this, but the simple explanation is it makes life easier) If you follow the general rule of thumb for long life of your batteries, you'll keep the discharge to 50% of total capacity so you'll have 100 amp hours of usable stored energy. I have a similar (or the same) ARB fridge and my experience is that it uses between 10 and 25 amp hours over night. The difference comes from ambient temperature and the setting of the fridge - I do use one of the insulating covers and I make sure to keep the vents of the fridge clear for air flow. How quickly your solar array will recharge the batteries depends upon how cloudy it is, how long the day is, are you in the shade or open sunlight, and the angle of the panels relative to incoming solar. Assume a sunny day with the panels in the open and flat, you can count on 15 to 20 amps (possibly more) for 4 to 6 hours which will produce 65 to 120 amp hours (actually a bit less due to efficiencies, tapering charges, etc, but those may be compensated for by the additional input from morning and afternoon hours). Some of those amp hours will be used running the fridge during the day and the remainder will recharge your battery bank drawn down during the night. Even the low estimate (65 amp hours) will take care of the fridge (day and previous night).

The challenge comes when it is cloudy, you get tired of parking in the sun all the time, etc. Those are the conditions where having a monitor can help - you can tell when things are getting down towards the 50% discharge and make an effort to get the battery bank fully charged up. I'm assuming that you have your two blue tops isolated from a third starting battery? If not the whole equation changes (I wouldn't have a permanently combined house-starting battery bank myself, but others like that set up).

Howard Snell

 

[65BAJA]

Thanks for the reply. The batteries are isolated with a Boat switch. I have it on (house connected to starter battery) when the Jeep is running. Whenever I stop I switch to off so there is no connection to the starter battery.

 

[Howard70]

Hello 65Baja:

A couple of things I forgot to mention. The ARB fridges often have a low voltage cut off - designed to shut the ARB down when the incoming voltage gets low. This can protect the compressor from trying to run with insufficient voltage. The problem is that the voltage at the ARB can be quite a bit lower than the voltage at the batteries if the run is more than a few feet and the wire gauge is thin. I'd use 12 gauge wire to connect the ARB to the batteries to prevent this - the effective length of the wire is more than we usually assume - it includes the complete circuit (positive and negative legs) so that usually means twice the distance between the fridge and the battery.

Your set up with the boat switch was a good way to go when you didn't have as powerful a solar array as you have now. You could consider keeping that switch off (batteries isolated) unless you need to parallel them. That would allow your house batteries to be charged completely by the solar controller. The solar controller should have a three stage charge sequence specific for AGM batteries. That charge sequence will probably give you longer life for the house batteries than charging them through the vehicle alternator. That assumes you have the solar array permanently mounted and working all the time. If you use your solar panels as a portable array, deployed only in camp, then you might need to augment the array with the alternator. If that's the system you use, then a monitor can be important to help you manage the distribution of charging done by the solar array and the alternator.

Howard

 

[65BAJA]

My Fridge is an old school one. About 14 years old. No auto anything. lol.

I've been reading HandyBob's Blog all day and now I think I should have bought a different charge controller and I should buy a battery monitor to keep a better eye on my batteries.

Eric.

 

[65BAJA]

Returning the Grape Solar charge controller tomorrow. It faulted out in my driveway charging my 2 batteries. It was a hot day so it may have overheated but now I don't trust it. I've read good things about the TriStar controllers from Morningstar so I now have a Morningstar TS-45 on order. I also ordered a Trimetric TM2030 monitor. No inverter yet though. I'm wondering if I can get away without one. When I camp everything I have is 12V. Computer charger, cell phone charger, fridge, HAM radio, and r/c car battery chargers are all 12V.

 

[unseenone]

+1 on the Morningstar, but it is not meant to be mounted outside, it needs to be mounted out of the weather. Order the temp sensor for it, you can cut it, and use the extra wire for the voltage sensor.

In the vehicle I did the Prostar PS-30, it's a bit more compact, but not MPPT.

I have the MPPT-45 it's a nice unit.

No interference on HAM with either, though the PS-30 is specifically designed for quiet operation (no rfi).

Good Choice.

 

[65BAJA]

The batteries will be in those plastic battery boxes. They will be mounted behind the front seats in my Cherokee. The charge controller will be mounted to the top of one of the boxes and the monitor will be mounted to the top of the other. There is a charge lead coming from the starter battery into the cab to charge the batteries while I'm driving. It has a fuse on the hot lead at the starter battery. Currently these leads are only 10awg I want to re wire them with at least #6 if not #4. Each battery box has an on/off marine battery switch.

Right now I'm rethinking how I want to wire everything. I know I'm guilty of a few mistakes at the moment. Like the way the two batteries are wires for charging. Right now the way it's set up I'm charging one battery and the other battery is just paralleled to that. I've read that is wrong. I should have the charger connected to the positive of one battery and the negative of the other battery so they both get an equal charge. So I have some things to work on when the new equipment gets in.

 

[unseenone]

If you connect to the positive on one battery to the negative on the other, you would be doubling your voltage. I do not think you want to do that in this case.

Making the assumption you are running 12v batteries, you don't want to do that. Just wire them + to + and - to -. You'll double your amp hours while keeping your voltage at 12v.

To calculate the needed wire size for charging, you should calculate the distances of the wire run.

 

[65BAJA]

Hmm. Maybe I worded that wrong. The batteries are paralleled. + to + and - to -. I was thinking about how the charger should be hooked to the paralleled batteries.

 

[unseenone]

Just connect it to the + and - Keep the wire the same length for the connection to each battery to battery connection. Here's how I did mine.

 

[65BAJA]

Morningstar controller came in today.:wings: Battery monitor won't be here until next week some time though.:mixed-smiley-030: I did order up some ANL fuse holders with 100A and 150A fuses. I have an inexpensive 400W inverter with a surge rating of 1000W. At 400W I should be drawing a little over 33A@12V I think. Should I fuse the feed line for the inverter with a 50A fuse (I would need to buy some 50A fuses) to cover the ~33A draw or should I use a 100A fuse to cover the ~83A that the surge rating will draw? Also ordered a battery temp monitor for the TriStar. Waiting on those as well.

Anyone running Optima batteries have any advice on what to set the TriStar to for charging? It can be set from 14V up to 15V.

 

[Hilldweller]

You're right to connect the charger to + on one battery and - on the other.

I ran two Optima D31M batteries for my ARB for 3 years and finally killed them from too many deep cycles. Had the fridge set to 11.5v and forgot to plug back in at home a couple of times. Poor batteries.
They're 150A for the two of them, not 200A, btw. And they do not like to be deep cycled like golfcart batteries. Personally, I'd never let them fall below 12.5v at the lowest.

I now have two Walmart group 31 boat batteries, flooded maintenance-free, 122A each. I've got the Renogy 100w Suitcase feeding them and it's kept them fully charged so far. My fridge is more efficient than yours but you've got lots of amperage from your panels. My panels peak at 5.6A.

Sorry I can't comment on your new controller. Just wanted to warn you to keep your Optimas fed and fully charged. They do recharge very very quickly compared to other batteries and can take a royal pounding.
I'd set the controller to AGM, 14.4 volts. If it doesn't have a setting like that we can get OptimaJim to ask Tech at Optima for you.

 

[65BAJA]

Thank you for the reply. I only have the Optimas because I could get them at cost where I used to work. I would not buy them again. Especially after a recent experience with their so called "tech support". I e mailed asking what my charge controller should be set to for a full charge. They copy pasted the .pdf that I had already read on their website. I replied asking for clarification because I didn't think it answered my question. The support lady re pasted a section of what she had already sent me without explaining or clarifying anything. I asked what their super duper wiz bag charger charged the battery at. They told me that info was proprietary. It's like they were going out of their way to be as vague as possible and not answer my question. I am pretty disappointed with them.

I did a little research on AGM batteries. I found Lifeline batteries. They have written a big 38 page pdf on how to take proper care of their batteries. It explained in great detail what the bulk charge rate is, what the absorption rate is, and what voltage a "fully charged" battery is at. :clapsmile

I would go with less expensive flooded batteries next time but the battery bank is mounted in the cab of the Jeep behind the seats. I should be able to start assembling everything this week. My battery monitor should be here Wednesday or Thursday. I'm going to wait on the big pure sine wave inverter for now. I have an espresso machine I want to be able to power for morning coffee. I sent them an e mail asking about mod sine wave and pure sine wave. I wasn't really expecting them to know. I received a reply within a couple hours. Apparently the boiler doesn't work properly on MSW. So if I want to relax with a nice espresso out in the middle of nowhere I need to get a PSW inverter with at least a 1000w rating. That's not going to be cheap. :Wow1:

 

[Hilldweller]

Sorry about the experience with their tech dept --- they always gave me really good/fast replies.
I'll ping Jim and have him get on the thread. He knows a bunch of stuff and he knows the people who know the rest.

BTW, my Optimas always leveled off at 13.1 volts after a charge and rest. When they were puppies the ARB would drop them to about .4v when the compressor kicked in; that makes a difference in the long run.