Running fridge fulltime.

[tyron]

Hey all,

I have a 120Ah (8 15Ah batteries ) battery pack in my car that my fridge runs off.

I only drive 20 min to work and back each day and anywhere up to 300 most weekends.

Currently my battery pack is only lasting about a week.

Does anyone else run a fridge fulltime without external charging or heaps of driving? If so what's your setup.

 

[sparra04]

My fridge stays on all the time
I do approx 200 ks a week
I use 2x 55amp optimas with a dcdc charger
Battery quality and how you charge them is most important

 

[Old.Tony]

The 15Ah batteries would be gel batteries. Charge them with more than 14.1V and you're killing them - bubbles form in the gel, which will never dissipate and will stop the flow of power. They also need to be slow-charged - about C/10 is safe, so each battery should get about 1.5A per hour.

20 minutes of driving is only going to put half an amp back into each battery. If the fridge draws 2A per hour (typical fridge on 50% cycle) over 24 hours it needs 48A, or 6A per battery. There's why it doesn't last long.

Things to try:

1) Put a voltmeter on the cable that you charge the battery with (without it being connected to the aux batteries) and see what voltage you're getting.

2) Put a multimeter in AMPS mode, remove the POSITIVE lead to the fridge, connect the black lead to the battery and the red lead to the fridge. Monitor the current drawn over a period. If you have one that can record data or connect to a PC for data acquisition then go for it and leave the fridge run for an hour, and average its power usage out.

3) Let the battery bank fully charge, then disconnect all of the batteries from each other. Wait an hour, then go measure all of the batteries with a voltmeter. They SHOULD read the same. If one is reading low, it will drag the rest of the pack down.

 

[Navmania]

My fridge stays on all the time
I do approx 200 ks a week
I use 2x 55amp optimas with a dcdc charger
Battery quality and how you charge them is most important

Hi Sparra. Do both your optimas run the fridge or is it only one out of a dual battery setup, I am running dual optimas and only use the second one for the fridge but I can only get two days out of it if I don't drive in that time. I am thinking of adding a bigger amp hour to the tub just for the fridge and then just use the second optima for the accessories. I have a 80l Waeco. Just curious about you setup.

Cheers.

 

[sparra04]

My 2optimas are linked together and I have a seperate craneker (3 batteries in total)
So I have 110 amps in aux power
I honestly believe the dc charger does a great job keeping them in top shape
It also depends on how much load you have on fridge and ambient temps

 

[Navmania]

Ok. That's what I will do but with one battery I think. I will also look Into being able to use solar panels to charge that battery also. I just need to work out the best setup for charging the third battery when driving and also be able to hook up solar when camping just for the fridge battery. I may need to hook up a solenoid to split it from the system when in camp them connect it back in line when driving or even find out if its best to keep it connected. I don't know if the second and third will equalize if left together?
I may need Old Tonys help on that one.

 

[sparra04]

Both redarc and ctec sell chargers that will automatically switch to solar charge when ign is off redarc have a very imformative website check it out

 

[terryc]

The c-tek D250S dc-dc charger is around $260 atm from looking something up a week ago.
You really need a dc-dc charger between alternator and batteries.

The output from the alternator can be all over the place and too high a voltage kills batteries.
Also, AFAIK, SLA charge/discharge rate is C/20 for maximum cycles.

8 in parallel is just asking for trouble. If one dies, it sucks the rest down with it. Unless these are freebies, then the price to purchase those will more than cover a decent 125 amphr Trojan wet cell.

Also, if you fridge in on 24x7, then that small amount of driving is most likely just no where near enough. If you park in the sun, then consider adding a solar panel.

 

[Navmania]

So if I run 3 batteries I'm better to run a charger for each Aux battery (2). I have a redarc bcdc 1220 on the setup I have and it works fine.
I will check out redarcs website. I didn't think to check there.

Cheers.

 

[Navmania]

I think this is what I was looking for. Pricy setup tho.

 

[Old.Tony]

Running batteries in parallel always presents the risk of one battery not performing as well as the others and dragging the pack down with it.

Solar panels are THE answer for many RVs. You do have to park in the sun and monocrystalline are better than poly - but a single roof-mounted panel will provide sufficient power to avoid the problem. You will need either a dedicated solar charger or the D250S as suggested by Terry (which would be my preferred choice for this setup).

Navmania, you can use a relay that is activated by the ignition (which should also be the source of the power for the charger) but this relay might have to power a further relay (higher current) to connect/disconnect the third battery. Again, with that many batteries you do run the risk of having one draw the others down.

Ideally the best way to handle the batteries is to charge them individually using an inverted mains supply (which the fridge will also use, and disconnect itself from the battery(s) while on mains power) - but this is an electrical nightmare. Simplifying the system by coupling the batteries together and using a single DC-DC charger (removing the inverter) does increase the risk of issues between the batteries but it's a risk we're generally happy to take.

The trick is to occasionally fully charge the batteries, then disconnect for an hour and measure the individual battery's voltage. If they're all the same, then the system as a whole is still in good condition.

If you find an AGM battery or a flooded deep cycle that is presenting a lower voltage when tested like this, run ALL of the batteries through an equalisation charging stage. NEVER use this on gel batteries (15V kills gel batteries). You should find that the batteries recover nicely unless they're too old, or one cell has suffered particular - and possibly manufacture-related - issues.

 

[happy john]

You probably have seen this pic before 120ah agm behind the seat of the 22 still room for other gear ect we run 40ltr engel as a freezer and a 60ltr as a fridge on long trips for 2 days with a 15min idle in the morning with the 120wt panel i can stay put for as long as i please without a big drive.

 

[Navmania]

You probably have seen this pic before 120ah agm behind the seat of the 22 still room for other gear ect we run 40ltr engel as a freezer and a 60ltr as a fridge on long trips for 2 days with a 15min idle in the morning with the 120wt panel i can stay put for as long as i please without a big drive.

That is one impressive battery. I have seen that pic before. Is that your second battery or is it a third one. How is your charging setup for that one using the solar aswell.

Thanks Old Tony. My dual battery setup is designed so I can rotate the battery's once every six months or so to try and give them an equal run at life. A bit like rotating the tires but the third one will be a bigger amp hour so I think a completely independent system for charging mite be the best way to go.

 

[Old.Tony]

If your battery sizes aren't identical (and it's also good to use batteries of a very similar age in a bank) then separate charging is really the best way to treat them. The lower capacity battery will charge faster and present a higher voltage to the charger - so the charger will think it's done its job, leaving the larger capacity battery still wanting.

 

[boostin_7]

Do any of the dc to dc chargers have the option to plug into mains 240v to power the charger when available on site?

 

[happy john]

That is one impressive battery. I have seen that pic before. Is that your second battery or is it a third one. How is your charging setup for that one using the solar aswell.

Thanks Old Tony. My dual battery setup is designed so I can rotate the battery's once every six months or so to try and give them an equal run at life. A bit like rotating the tires but the third one will be a bigger amp hour so I think a completely independent system for charging mite be the best way to go.

Hey mate i could have 3 batts but the safari snorkle robbed all the space but when i camp without the van it works well when towing i link the two agms in nav and van via a anderson plug so 240am/h the two andersons on the front and rear of van and the nav allow me to camp in the shade and charge both via the anderson extension lead 10mtrs
Regards
John

 

[mike1303]

Redarc is a lot cheaper on fleabay mate I have the bcdc1240 in mine with two AGM 125ah and a 80l waeco on full time
Works a treat. There are cheaper options avaliable

 

[Navmania]

Yeah eBay is cheap. That's where I got my redarc from and have already had a look for the 1225 which has the solar input. It is heaps cheaper on there.

 

[tyron]

Thanks Guys,

For now I will leave it and just turn the fridge off when I dont really need it. Thinking I will get a solar panel and mount it under the nissan roof racks at some point.

 

[d40ryan]

im currently running the redarc d250s 110w mono panel and a 200ah agm as my second bat. i run alot of shit and it hasnt missed a beat yet. bonus with the d250s is once it has filled the agm batt it charges the starter batt so i never need to jump.

smart chargers are the way to go, i wouldnt buy another solenoid.