BENT ARROW
CO.
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I have 2 Exide3600 6 volt from Sams Club, the web site shows 186AH @ 20 amps for each. I will be adding 4.16 amps an hour for 8 hours each night to run a CPAP air pump for my wife while we hope to continue boondocking. My problem the web site had min at 25 amp and AH at 20 amps which did not seem to add up even close. I was thinking the min means minutes which were listed something like 360 at 25 amps.
We have the MH gen we run 2 to 3 hours a day.
I should add "PLEASE" since we may need to stop boondocking.
Bent Arrow
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tatest
Oklahoma
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360 minutes at 25 amps is 150 AH.
186 AH at 20 amps, that's the normal method of rating.
Those two numbers are consistent. The number of AH available decreases with discharge rate.
What you should really be interested in is the AH rating at 5 amps draw, closer to what your CPAP uses. That's probably over 200.
But consider only 50% discharge, to preserve battery life. Still, you will have enough energy stored to run the CPAP for about 20 hours.
Tom Test
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tvman44
Southwest Louisiana
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You should have no problem.
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Hurricaner
Hurricane Utah
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You have 20 / 186 = 9.3 amps. So you can draw 9.3 amps for 20 hours. You should never take the batteries below 20% DOD so you would have about 16 hours at 9.3 or 32 plus hours at 4.5 amps. What kind of charger do you have to get them back up in 2 to 3 hours?
Sam
Sam & Kari
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smkettner
Southern California
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You will make the night if you have a full charge on the battery.
Are you charging with a good multistage converter or inverter/charger?
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hwybnb
Southern California
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I haven't seen the answer that explains things clearly (IMO) so let me try.
Deep discharge batteries are rated for x amp-hours at y rate because the capacity is a function of the discharge rate. When you run at a high discharge rate you get fewer usable amp-hours than you would at a lower rate.
The important thing is how many amp-hours you need. If I understand your post correctly your machine draws 4.16 amps and you want to run it for 8 hours. Multiply those two numbers and you get 33.28 amp-hours.
The rated capacity is based on reaching full discharge. To maintain good battery life you should avoid going lower than 50%, but you can go as low as deep as 80% if necessary without killing the battery. If you hold to the 50% level you have 93 amp-hours to use, so your load is about 1/3 (35%) of that. You will be fine.
* This post was
edited 07/03/09 03:03pm by hwybnb *
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BENT ARROW
CO.
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The gen is a Onan 5500, not sure about the converter but we have gone 3 days using the lights and water pump without skimping and the batteries will still be in the green on the panel before charging. I plan on a small inverter added to the bedroom with direct lines from the batteries.
Thanks for the replies and help, I never considered or even thought of the discharge changing the rate.
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californiatraveler
Goleta,Ca 93117
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HWYBNB has the facts right on ! You need a digital voltmeter to keep check on the battery voltage. The led indicators are not very accurate. Try Radio Shack, they have some good ones for not very much. The air pump draw is ok, but what else do you run at night ? A TV,lights,and the gas detector draws about .10A, and you most likely have a carbon monoxide det.also, .10A ? You should think about ditching the "convertor" and get a good 3 stage battery charger. It will take much better care of your batterier, and actually charge them properly up close to 100% Start with the meter. Your 12volt should not go below about 11.5volts, and it needs to be charged when it gets there for sure. take care, and have some good trips to interesting places !
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Deen
Vancouver, WA
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We have 4 Interstate U-2200's (about 230 amp hours each), since we drawing 12 volts you take the individual rating times 2 (460), then, since you don't really want to go below 50% you halve that so it's actually 230 amp hours. We can only go about 8 hours between charging the batteries as we use as many lights as we want, both TV's if we want and usually a laptop, the U-line ice maker and the 100# refer/freezer in the storage bay and maybe the DVD, CD or VDR. Not real economical on battery power, but we ordered it to occasionally boondock, not full timing it in the wilds. Oh yes, I also run my CPAP at night.
We regularly run the batteries down to 12.0 or 11.9 volts and the batteries ar just over 7 years old and still functional.
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wa8yxm
Wherever I happen to park
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I"m used to seeing the 20 hour, not the 20 amp amp hour rating, And 186 would be low for that class of battery
NOTE: when you figure the amp hour capacity of a pair of six volt batteries in series it is very easy 2 186 amp hour six volt batteries in series give 186 amp hours at 12 volts. (NOTE the same rating)
YOur machine is 4.16 amps, times 8 hours = 33.28 amp hours (Simply multiplication)
Your batteries should be, by my standard (the 20 hour rate) 220 amp hours but to use your 186 amp hour figure you have 93 usable amp hours.
So ,,,,,, Figure in the rest of the loads on the unit and do the math
I think you will be good.
Nothin adds excitment like something that is none of your business
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