How low can a battery go?

Submitted: Monday, Apr 19, 2004 at 17:20
ThreadID: 12194 Views:1863 Replies:8 FollowUps:12
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I have just fiited a dedicated plug and wiring for my fridge. I also added a volt meter at the fridge outlet so I can keep an eye on how the battery is going. My question is how low can I let my battery voltage fall on a regular basis before it will start to cause damage. My batteries are Century N70 Severe Service and I isolate one when stopping at camp. Note that I don't have a Deep Cycle.

Thanks,

Topend
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Reply By: Peter 2 - Monday, Apr 19, 2004 at 17:28

Monday, Apr 19, 2004 at 17:28
It is not only damage to the battery you should be worrying about, you can/will also damage the frig with low voltage as well. Most decent frig's will cease operating when the voltage reaches a point where damage will occur. This is usually around the 11 volt mark.
The 11 volt mark would be a good point to stop draining the battery too. Virtually every time you flatten a battery you decrease its lifespan, best not to do it. Deep cycle and gel cells are designed to handle being drained but it still has an efffect on lifespan.
Peter
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Follow Up By: Topend - Monday, Apr 19, 2004 at 17:35

Monday, Apr 19, 2004 at 17:35
11 volts is what I was thinking. The fridge (Waeco CF110) cuts out at less than this, hence the volt meter so I can cut it sooner.

Topend
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Follow Up By: David N. - Monday, Apr 19, 2004 at 18:16

Monday, Apr 19, 2004 at 18:16
Draining the battery too far will severely reduce it's life- even more so if it's not a deep cycle.
Low voltage won't however affect your Danfoss powered frige- the compressor is designed with a low voltage cutout and will NOT be harmed by running down to the low voltage cut off point....
There's lot's on the subject of discharging batteries if you do a search, however basically if you want your battery to last don't discharge to less than 30% charge remaining for a deep cycle battery..... starting batteries should be discharged far less than that or you'll be throwing them out very quickly indeed..
You can't really work JUST on voltage as that will vary tremendously depending on the amount of load when it's measured.
(approx 11.6v off load is dead FLAT, but under load it would be less volts)
Cheers
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Follow Up By: Peter 2 - Monday, Apr 19, 2004 at 18:58

Monday, Apr 19, 2004 at 18:58
Yes agree that there will be no damage to frig's with a voltage cutout but some older ones don't have one. I should have reread my post to avoid confusion ;-))
On a not unrelated subject never connect the negative connection of any accessory direct to the battery negative terminal unless you are going to fit a fuse to both negative and positive legs.
The reason for this is that if for some reason the chassis/engine end of the negative/earth/ground cable is disconnected/broken/high resistance when you try to start the engine excessive currents will flow through the accessory, which usually means they are stuffed. I've seen quite a few HF radios fried because of this over the years as they usually have a decent size cable which can carry the current, but pretty much any accessory is susceptable.
The best place to connect the negative from any accessory is either at the engine/chassis ground end of the negative lead or preferably nearby.
Peter
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Reply By: ThePublican - Monday, Apr 19, 2004 at 17:36

Monday, Apr 19, 2004 at 17:36
Topend ,, well covered in the archives ,yet the 'best ' is at www.uuhome.de/william.darden/carfaq.htm anything and everything any one would ever want to know about batteries,,
AnswerID: 54986

Follow Up By: Member - Nigel (QLD) - Monday, Apr 19, 2004 at 19:33

Monday, Apr 19, 2004 at 19:33
nah www.batteryfaq.org is better :)
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Reply By: ThePublican - Monday, Apr 19, 2004 at 17:43

Monday, Apr 19, 2004 at 17:43
Topend..my waeco handbbook page 13,
low 10.4
med 11.0
high 12.0 cutout
AnswerID: 54990

Follow Up By: Member - Nigel (QLD) - Monday, Apr 19, 2004 at 21:21

Monday, Apr 19, 2004 at 21:21
very handy feature - the adjustable cutout

remember the cutout is the voltage at the fridge so the actual battery voltage will be higher (more so after it has rested).

high is good for running of a starter battery
med is good for deep cycles
and low if for when you want to flatten the battery :)
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Reply By: Member - Nigel (QLD) - Monday, Apr 19, 2004 at 19:32

Monday, Apr 19, 2004 at 19:32
it depends how long you want your battery to last.

ie if you always stop at 12.10 volts (50%) your battery will probably last twice as long as it will if you take it to 11.80 volts (30%). I try to keep mine above 50% but don't worry if I occasionally go to 30%.

But you must take the voltage reading after the battery has rested (ie no charge or load for a while), otherwise the voltage will be lower if under load, or higher if being charaged.

Going below 11.8 volts will drastically reduce the life of your battery (that's why deep cycle batteries only have 6 month warranties - coz that's how long it will last if you completely flatten it each time).

You should get at around 18 months if you only got to 30% and 3-4 years if you stay above 50%. Of course other factors also come into play like heat and vibration - if your battery is in a hot area then you don't wanna stress it by discharging it too much.
AnswerID: 55001

Reply By: William - Monday, Apr 19, 2004 at 20:13

Monday, Apr 19, 2004 at 20:13
a battery can go as low as a catfish or NSW policemen. Both have one thing in common is that they are bottom dwelling scum suckers.
AnswerID: 55018

Follow Up By: ianmc - Monday, Apr 19, 2004 at 22:22

Monday, Apr 19, 2004 at 22:22
They are coming to get you William and a good thing too!!!
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Follow Up By: The Publican - Tuesday, Apr 20, 2004 at 20:42

Tuesday, Apr 20, 2004 at 20:42
NSW police are pigs that lie and are corrupt.
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Reply By: ianmc - Monday, Apr 19, 2004 at 22:24

Monday, Apr 19, 2004 at 22:24
I have had a Delkor starter battery for just on 4 years and have run the Waeco off it & have discharged it right down a few times thru misuse & it still works fine.
Maybe its a better bet than some of these deep cycles!
AnswerID: 55054

Follow Up By: Topend - Monday, Apr 19, 2004 at 22:34

Monday, Apr 19, 2004 at 22:34
An auto electrician once told me not to get a deep cycle. Cost too much, can't buy them at an outback servo if you need a replacement and a normal battery will work just fine if you manage the amount of discharge.
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FollowupID: 316749

Follow Up By: Flash - Tuesday, Apr 20, 2004 at 20:26

Tuesday, Apr 20, 2004 at 20:26
and....
he'll sell you a new battery sooner!!!
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FollowupID: 316923

Follow Up By: Topend - Wednesday, Apr 21, 2004 at 15:05

Wednesday, Apr 21, 2004 at 15:05
I don't buy batteries from an auto electrician so his opinion is unbiased. I tend to agree with him as I have used Trailblazer and my Waeco CF110 for 8 or 9 years on standard batteries without a problem.
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FollowupID: 317099

Reply By: Topend - Monday, Apr 19, 2004 at 22:29

Monday, Apr 19, 2004 at 22:29
My volt meter is at the fridge, not the battery so the volts I refer to are with the fridge on and under load. I will buy a solar panel before our next trip but it is still handy to know how low I can safely run my battery down without reducing it's life significantly.

My fridge doesn't have the switch to adjust the cutout. It cuts out at the lower value which is too low.

Thanks for all your replies.

Topend
AnswerID: 55056

Follow Up By: Member - Gajm (VIC) - Monday, Apr 19, 2004 at 23:22

Monday, Apr 19, 2004 at 23:22
I have one of the battery over discharge protectors connected between the fridge and cig outlet, it cuts the fridge off automaticaly at 11.8 volts, they cost around $25 at K-mart if you can find them, or $30-$35 at 4x4 outlets. It's a good back up.
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FollowupID: 316755

Follow Up By: Member - Pesty (SA) - Tuesday, Apr 20, 2004 at 00:25

Tuesday, Apr 20, 2004 at 00:25
Hi Topend
I have a 110 and mine cuts out at 11.6 volts which I thought was a little hi as the waeco book says 10.6. I would be happy at around 11.0. I think you would be strugling with a solar panel if you live in the topend. I carry a small gen when on extended trips and just put it on once a day if not driving, this puts 10amps into the battery and runs fridge on 240 while i am running gen., usually a tank of fuel 4-5 hours. I turn fridge up while on 240 to pull temp down very low. Use 90ah optima deep cycle gell cell bat for fridge. Optima rep recon I could get 8-10 years from it but I dont think he is in the real world!

Cheers Steve
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FollowupID: 316757

Reply By: Topend - Tuesday, Apr 20, 2004 at 05:57

Tuesday, Apr 20, 2004 at 05:57
I just run the fridge over night and put a bottle of water in the freezer as a test. The bottle froze and the battery is still showing 12.5 volts. The battery over discharge protector from K-mart sounds like it is worth a try. After reading above responses I will try not to let voltage fall below 12 volts.

Topend
AnswerID: 55081

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