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-   -   Basic question about field batteries (http://www.Wattflyer.com/forums/showthread.php?t=72733)

FlyWheel 12-05-2013 03:35 PM

Basic question about field batteries
 
How do you determine the amp/hour rating of a deep cycle battery? I was at Wally World yesterday looking at batteries and not one (marine, car, motorcycle, none) were rated in amp/hours, milliamp/hours or any other understandable fashion. At least not by us 'normal' electrical folks. How does one determine the capacity of these batteries? Is there some sort of special code I should be looking for, and how is it translated into something that makes sense?

Yakfishingfool 12-05-2013 04:39 PM

FYI - A new apples to apples system??


http://www.batterystuff.com/kb/tools...oup-sizes.html

solentlife 12-05-2013 04:40 PM

Quote:

Originally Posted by FlyWheel (Post 933210)
How do you determine the amp/hour rating of a deep cycle battery? I was at Wally World yesterday looking at batteries and not one (marine, car, motorcycle, none) were rated in amp/hours, milliamp/hours or any other understandable fashion. At least not by us 'normal' electrical folks. How does one determine the capacity of these batteries? Is there some sort of special code I should be looking for, and how is it translated into something that makes sense?

I have a simple answer : I would not buy such an item at Wally World. The better place to go especially in USA is an RV or Boat dealer who sells support and spare parts gear. Get the proper article.

Anyway - if you insist ... they MUST have a label somewhere saying A/hr .... it's usually listed separately but also in the overall spec name ...

ie : 12v80A/hr120a or similar ... meaning 12V .... 80 Amp.hr ..... can sustain 120 Amps for xxmins .... etc.

Nigel

kyleservicetech 12-05-2013 05:37 PM

Quote:

Originally Posted by FlyWheel (Post 933210)
How do you determine the amp/hour rating of a deep cycle battery? I was at Wally World yesterday looking at batteries and not one (marine, car, motorcycle, none) were rated in amp/hours, milliamp/hours or any other understandable fashion. At least not by us 'normal' electrical folks. How does one determine the capacity of these batteries? Is there some sort of special code I should be looking for, and how is it translated into something that makes sense?

The question is - how many amps are you planning to pull out of your deep cycle battery while charging your models batteries?

IMHO, and from personal experience, those deep cycle batteries, even the 120 Ampere hour rated units should not be discharged at more than about 20 Amperes. Any higher, and you'd better plan on replacing your deep cycle battery once or twice a year.

I've purchased deep cycle batteries from Wally World, didn't have much good luck with it. If the battery doesn't indicate how many ampere hour capacity it has, go elsewhere! Also, if the battery has "Cold Cranking Amps" stated on it. You're likely looking at a plain lead acid battery with a "Deep Cycle" name plate on it.

Here is a bit more info on this subject:
http://www.wattflyer.com/forums/showthread.php?t=65723

FlyWheel 12-06-2013 12:09 AM

Thanks. I have a small charger and will only be charging 3 cell LiPos at a time. I just want to be able to figure how many times I can do this before I start draining the battery too low (I may not even need a very large capacity battery).

Last question on this: I never intended to get a relabeled no-name brand at wally world, but where would I get a better deal? I know both boats and RVs use these batteries, but would a battery for one cost more (waterproofness?) that the other, even though they both may have the same capacity?

hayofstacks 12-06-2013 01:23 AM

I used to charge 3-6 3 cell lipos at a time in my station wagon when I went flying. I just popped the hood and hooked up 3 clip on chargers under the hood, and had 3 cigarette lighter chargers in the car. one in the front cigarette lighter plug, and one in each rear door. I had 7 1800 mah batteries charging at 1-2 amps each, and I could fly 2 planes continuously very rarely waiting for batteries. I always went out for 2-3 hours or more. I think my record was 9 hours.

no special battery tricks or anything. just an old 88 crown vic with an interstate battery. I never even started the car to charge up the battery. I did have a small harbor freight jumper box for the just in case I did over charge or left my head lights on.

one time I was running a junk battery and only had my spare keys, which didn't have a trunk key, where I kept the jump box. I had my 4000 mah 3 cell on me, so I hooked some alligator clips to it to the battery to pop the trunk. I couldnt help but try to crank it just to see what happened.it did crank the car over once or twice, but it also melted both alligator clips. ill bet with a thicker jumper it would have started it.

kyleservicetech 12-06-2013 05:36 AM

Quote:

Originally Posted by hayofstacks (Post 933252)

one time I was running a junk battery and only had my spare keys, which didn't have a trunk key, where I kept the jump box. I had my 4000 mah 3 cell on me, so I hooked some alligator clips to it to the battery to pop the trunk. I couldnt help but try to crank it just to see what happened.it did crank the car over once or twice, but it also melted both alligator clips. ill bet with a thicker jumper it would have started it.

Yeah
Somewhere in youtube, a guy has a car with a completely dead battery. The video shows him connecting an A123 pack to the dead battery, waits for a minute or so, and starts the car. This was in Canada, in very cold weather.

Our LiPo and A123 batteries do have a very high current capability, if only for a few seconds. At any rate, my old Chevy S10 starter pulls about 120 Amps, not that much over what some of these higher powered electric motors pull.

kyleservicetech 12-06-2013 05:45 AM

Quote:

Originally Posted by FlyWheel (Post 933247)
Thanks. I have a small charger and will only be charging 3 cell LiPos at a time. I just want to be able to figure how many times I can do this before I start draining the battery too low (I may not even need a very large capacity battery).

Last question on this: I never intended to get a relabeled no-name brand at wally world, but where would I get a better deal? I know both boats and RVs use these batteries, but would a battery for one cost more (waterproofness?) that the other, even though they both may have the same capacity?


H'mmm
Lets see. Lets take a three cell 2500 Mah Lipo battery. Safe charging current would be 2.5 Amps for one hour. And, at 4.2 Volts per cell, and three cells, charging power would be 2.5 Amps times 4.2 Volts times three cells, or 31.5 Watts. Most chargers have about 85% efficiency, so the watts out of your deep cycle battery would be 31.5/0.85 or about 37 watts.

Watts equals volts times amps, or Amps equals watts/volts. For a 12 volt battery, that would be 37/12 or just over 3 amps. If you pick up a 70 Ampere Hour deep cycle battery, and never draw over 50% of its capacity, that would be about 35 Amp hours. And at a 3 amp draw, that would be about 11 hours of discharging time.

So, a standard 70 Amp Hour deep cycle battery would provide a full days flying, at one flight per hour that is. This is the main reason many folks using LiPos have several battery packs available. It's also the reason all but one of my models use the heavier, larger, lower voltage A123 cells. These cells can be recharged in 10 or 15 minutes. But for the bad news, if you've got a 12S2P A123 pack, my experience shows that charging one of these battery packs as a 6S4P pack at 30 Amps with a 120 Ampere Hour deep cycle battery will kill that deep cycle battery in a few months. (The A123 battery charger is pulling about 50 Amps out of the lead acid battery!)

solentlife 12-06-2013 08:06 AM

Quote:

Originally Posted by FlyWheel (Post 933247)
Thanks. I have a small charger and will only be charging 3 cell LiPos at a time. I just want to be able to figure how many times I can do this before I start draining the battery too low (I may not even need a very large capacity battery).

Last question on this: I never intended to get a relabeled no-name brand at wally world, but where would I get a better deal? I know both boats and RVs use these batteries, but would a battery for one cost more (waterproofness?) that the other, even though they both may have the same capacity?

If you really want to go this route ...

Get yourself to a Junk yard .. where they scrap old cars / trucks etc. You can pick up good batts cheap ... and if it only lasts a season or 2 - what have you lost ?

Even though I know about Lead Acid batts .. family having boats and RV's all my life - I don't buy over-rated over-priced gear ... I buy my batterys from scrap yards ... for my boats. My present cruising yacht has 2 100A/hr batterys and they are now over 4yrs old and still in excellent condition .. starting a 43HP diesel ... powering domestic and navigation gear for days ...

Next is to find a Truck Dealer who supplies batterys for trucks ... they do types that not only start diesels, but also power the hydraulic tail-lifts. Designed for both low and high power demand.

Next is to find a Golf Cart dealer and the supply of 6v packs that get put in series to provide 12v .. they are designed to carry fat b*****ds around 18 holes all day !

Then we get to normal retail outlets .... RV and Boat shops - they deal in this everyday for keeping Mum and Kids happy in their trailers / boats etc.

Bottom of the list is Wally World and similar - who sell the compromise form battery that will soon give up under stressed loads. I know there are probably loads of people out there still using their WW battery after xx years ....

One avenue that is forgotten ... a small battery can be used - even one that has given up starting your car ... for small - medium packs at less demanding rates ... by connecting up a relay charge circuit .. so when you have engine running - it is being charged up. Stop engine and relay drops out ... you use for charging lipo's.

A good book on all this : >

http://www.amazon.co.uk/Practical-Bo.../dp/0713661496

It may be about boats ... but has a wealth of easily understood information about battery types, charging .. discharging ... etc.

Nigel

FlyWheel 12-06-2013 08:46 PM

Thanks peeps. Living in the Southeast as I do, junk yards are NOT in short supply neither are repair shops or are places that service trucks. And of course we'all know The South is the uncontested RC capitol of the world! :D


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