batteries

HI ALL
Have a optima AGM 55AH battery and was wondering if it was fully charged would it keep a 40LT compressor fridge/freezer going all night with out being hooked up to a charger. I know it's not ideal but I already have this battery.
Opinions Appreciated.
THANKS
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Reply By: ABR - SIDEWINDER - Thursday, Feb 23, 2012 at 16:31

Thursday, Feb 23, 2012 at 16:31
Yes depending on the make of fridge it will use about a 3rd of the battery capacity for a overnight stop. (12 hrs approx)

Regards

Derek from ABR
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Follow Up By: Allan B (Member, SunCoast) - Thursday, Feb 23, 2012 at 16:58

Thursday, Feb 23, 2012 at 16:58
.....and if it is operating as a fridge, not a freezer.

Cheers
Allan

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Follow Up By: ABR - SIDEWINDER - Thursday, Feb 23, 2012 at 17:00

Thursday, Feb 23, 2012 at 17:00
quite right yes...

also ambient temperature and amount of times it is opened etc.

there are many variables.

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Follow Up By: Swaggy1963 - Friday, Feb 24, 2012 at 00:16

Friday, Feb 24, 2012 at 00:16
Hi there this is totally unrelated to this post its a question for derek from abr sidewinder I have seen solar panel carry bags on ebay carrying the abr sidewinder brand yet I am unable to find them anywhere else on the net as they dont have the size I want on ebay just wondering if these are actually an abr sidewinder product.

cheers
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Follow Up By: ABR - SIDEWINDER - Friday, Feb 24, 2012 at 07:48

Friday, Feb 24, 2012 at 07:48
Hi Swaggy

Yes they are a ABR-SIDEWINDER product, there are limited sizes and as we have discontinued solar panels due to the flood of the market with cheap panels we are selling out the bags and will not be making any more. Email me with the size of your panel and I will see what I have to help you.

Regards

Derek from ABR
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Reply By: Member - Phil G (SA) - Thursday, Feb 23, 2012 at 18:41

Thursday, Feb 23, 2012 at 18:41
One of my batteries is a 10 year old Optima Blue Top 55Ah and it was running a 40L Engel fridge for one day and 2 nights in the desert last August (cold at night). Like Derek says, there's lots of variables, but they are a great battery.
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Follow Up By: Dennis Ellery - Saturday, Feb 25, 2012 at 14:43

Saturday, Feb 25, 2012 at 14:43
I am interested in using an Optima as a deep cycle battery and am told that, when used in a cycling application, they need a 2 to 3 amp finishing charge for 1 hour after being fully charged.
10 years is good – do you follow that charging recommendation?
Cheers Dennis
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Reply By: mangey33 - Friday, Feb 24, 2012 at 14:55

Friday, Feb 24, 2012 at 14:55
I have an Optima 55AH yellow top and it runs my 60L Evakool for about a day and a half before i have to start the ute .
Cheers
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Reply By: bobjtls - Saturday, Feb 25, 2012 at 01:05

Saturday, Feb 25, 2012 at 01:05
I am a newbie at fridges and batteries and have an enigma. I have just bought a 130amphour gel battery. My fridge is a chescold and the plate on the back says that its power rating is 75watts at both 12 and 240 volts. So from my simple maths, at 12 volts, the fridge should draw approx 7 amps and at 240 volts, it should draw approx 0.3 amps. So, if my understanding is correct, then at 240 volts, via an inverter, the battery should last approx 433 hours or 18 days. Seems a dream!

I presume that we should not let the battery run down completely, so even if we allow a 30% residual charge to remain, then the fridge still should be powered a considerable time. Continue dreaming!

However, today i put the whole kit together and the fridge ran from mid day to about mid night before the inverter's alarm rang to indicate low battery voltage (approx 10 volts). I had a power meter attached to the 240 socket on the inverter and it showed that the fridge really drew 0.3amps and approx 75 watts every time I looked. A rude awakening.

So can someone explain what is going on here? Where is my understanding wrong or my maths faulty? How can some replies to questions like this claim several days running off a battery? I have also tried plugging the fridge into the battery's DC socket and it ran overnight but by morning the battery was down to 40% charge(according to the battery charger when I connected it).

A very confused

Bobj
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Follow Up By: bobjtls - Saturday, Feb 25, 2012 at 01:27

Saturday, Feb 25, 2012 at 01:27
I should have added, the battery sits in a battery box. Should I direct connect the inverter to the battery and not via the battery box?

Bobj
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Follow Up By: Allan B (Member, SunCoast) - Saturday, Feb 25, 2012 at 08:59

Saturday, Feb 25, 2012 at 08:59
Well Bob, Watts is arrived at by multiplying the applied voltage by the current drawn, so you are correct with your calculations. However when the inverter is supplying the 75 watts (240V x 0.3A) then its input has to draw some 6.25 amps from the battery in order to supply that 75 watts ( 12 volts x 6.25 amps = 75 watts). In actual fact, due to the inverter efficiency of maybe only 80% then it will actually draw about 7.8 amps.

What fridge do you have that draws a continuous 75 watts? Those people claiming a battery support time of several days have fridges of much lower rating and probably operating in ideal conditions.

Cheers
Allan

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Follow Up By: Member - Sn00py2 (NSW) - Saturday, Feb 25, 2012 at 09:02

Saturday, Feb 25, 2012 at 09:02
Hi bobjtls,

Yes, your frighe is drawing .3amp @ 240 volt (75 watt) but for your inverter to produce that (allowing for heat loss and inefficiency in the inverter, it is probably drawing around 10 Amp (120 watts) from the battery.

I'm pretty sure your Chesscold is a 3 way fridge and not a compressor fridge so it will draw many many more amps than a compressor fridge. You really need to run it on gas when camped and only off the battery while travelling.

Remember, the key thing here is watts. If your inverter was 100% efficient then it would draw 75 watts (6.25 amps) when running directly from the battery and also 75 watts (6.25 amps) from the battery through your inverter.

Remember, there is no such thing as free electricity.

Regards,

Sn00py2
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Follow Up By: Member - Phil G (SA) - Saturday, Feb 25, 2012 at 09:53

Saturday, Feb 25, 2012 at 09:53
Bob,
Your 3-way Chescold fridge consumes about 4 times as much electricity as a compressor fridge (like Engel/Waeco etc). That is because your fridge needs power continuously, while the compressor fridges work the same as your house fridge - they only run when they need to, and a compressor is more efficient anyway.

The 12V on your Chescold is really only suitable for when you're driving. They run very efficiently on gas, so when stopped, you'd have to take it out of your vehicle and hook it up to gas. Many people would find this a pain, which is one reason why compressor fridges are more popular with 4wd travellers. Don't be tempted to leave it in your vehicle and run off gas because of the explosion risk with LPG.
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Follow Up By: bobjtls - Saturday, Feb 25, 2012 at 15:39

Saturday, Feb 25, 2012 at 15:39
Thanks everyone for your comments and advice. I also talked to SSB who made the battery and they confirmed that the fridge would only run for about 12 hours on that battery.

They suggested that the battery would need a 150 Amp hour regulator, as a minimum, if I were to mount the battery in my Nissan Navara ute and they advised their dual battery kit, part number DBC150K, price $278. This kit, they said, contains everything I would need to mount the battery in my ute and have it charge successfully.

I have always planned to do that but may now have to bring that forward and also buy a new fridge.

Interestingly, even though its their battery and charging kit, they could not tell me how long it would take to charge the battery from a 10V state. I will call back next week to talk to the expert and if I get any answers will add them to this thread.

One other interesting snippet. They said the battery was a VRL-SLA type, so a lead acid battery. Battery Mart in Tempe, who sold it to me said it was a gel battery. Not sute how this affects charging but on my charging attempts, I chose gel battery as instructed by Battery Mart.

Thanks again for all your help though, its greatly appreciated.

bobj
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Follow Up By: Allan B (Member, SunCoast) - Saturday, Feb 25, 2012 at 15:53

Saturday, Feb 25, 2012 at 15:53
Bob, I wonder why you are speaking of recharging your battery from "a 10V state".

Allowing your battery to become discharged below 12.2 to 12.0 volts (about 50% battery State of Charge) is a sure way of destroying the battery,

Cheers
Allan

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Follow Up By: bobjtls - Saturday, Feb 25, 2012 at 17:18

Saturday, Feb 25, 2012 at 17:18
Alan,

the inverter has an automatic cutoff set at 10V and that is where I got the figure from as I could easily see the situation wherein you let the battery run the fridge until it cutsoff.

bobj
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Follow Up By: Allan B (Member, SunCoast) - Saturday, Feb 25, 2012 at 18:41

Saturday, Feb 25, 2012 at 18:41
Bob, That inverter automatic 10v cutoff is intended to protect the inverter from under-voltage. Using that cutoff to protect your battery will be disaster.

Try Googling "battery depth of discharge" for information regarding managing your battery properly

.
Cheers
Allan

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