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e-Electric Batteries & Chargers > SLA Rechargeable 12V field Battery Advice
 
 
HeliMan Dave
Heliman
Location: Chicago, IL USA

Hey guys.

I'm looking for some recommendations for a 12v Sealed Rechargeable Lead Acid battery to power my Cellpro 10s Li-Po charger.

It draws about 4-7A when charging my 6s (24.2v) 5300mAh Li-Po packs at 1C.

My YUASA 65aH SLA battery seems to have seen its better days as it will no longer hold a charge.

I'm guessing I should look for something similar in the 85ah range.

Thanks!


Dave D.
06-19-2008 07:41 PM
 
 
Rob_T
Elite Veteran
Location: Tualatin, OR - USA

You should be drawing over 10A when charging that battery at 1C. 65 to 85AH does sound about right for getting plenty of charges at the field.

If you don't need the spill resistance, then a marine battery will probably work out cheaper than SLA.


Rob
Eco8, Piccolo Fun, Shogun, HB Elite CP, Trex 450XL CDE, Swift
06-19-2008 08:51 PM
 
 
speeddemon370
Veteran
Location: Spruce Grove, Alberta, Canada

Between the trucks, motorbikes, rc's and powertools I've spent my fair share of time hunting down battery deals. I was lucky enough to find a place called battery world that solved all my problems. It was funny how a guy can spend all the time in the world either online or at walmart or napa or whatever but the most helpful advice and best selection came from a "mom and pop strip mall specialty store". I'd highly reccomend them but I'd be very surprised if they had a website. Battery World on 149St and 118ish ave. Edmonton/Alberta/Canada

with 2 ears and 1 mouth you should listen twice as much as you talk
06-20-2008 03:11 AM
HOMEPAGE  
 
 
HeliMan Dave
Heliman
Location: Chicago, IL USA

Hey guys.

I'm still researching batteries. Can you guys refresh my memory how to figure out # of charges based on current draw and capacity of battery?

I only need to get 3-6 (or a few more) charges out of the SLA or Marine Deep Cycle 12v battery at the field. My Cellpro 10s charger draws about 8-9A when charging my 5300mAh 6s packs at 1C and finishes them in about 50-60 minutes per pack.

I'm also thinking I might up the charge rate to 2C when in the field to shorten the recharge time. Most Li-Po's should not be charged at a rate higher than 1C however it's ok with the Cellpro packs.

I was trying to figure out if I can go as smaller than a 65AH SLA/Marine battery. There is a decent 55AH for $60 at a local battery place and at the other end of the spectrum is a 75AH Optima SLA for about $200.00

Dave
07-02-2008 07:14 AM
 
 
Rob_T
Elite Veteran
Location: Tualatin, OR - USA

Basically the watt-hours put into the battery you're charging will match the watt-hours taken from the charger battery.

Watt-hours are amp-hours (Ah) multiplied by voltage.

So to fully charge your 6S 5300 pack you need 6*4.2*5.3 watt-hours. Thats 133.56 watt-hours.

You 12V battery will be discharged by 133.56/12 = 11.13 amp hours.

So a 65Ah battery should give 65/11.13 charges - that's just under 6 full charges.

Charger's aren't 100% efficient, so you wont get as many charges as calculated (usually you get about 20% fewer), but you also probably wont discharge your battery fully so that tends to cancel out some of the efficiency loss.

Unless you're discharging your lipos more than most people do, I think 5 charges is a reasonable expectation.


Rob
Eco8, Piccolo Fun, Shogun, HB Elite CP, Trex 450XL CDE, Swift
07-08-2008 07:50 AM
 
 
HeliMan Dave
Heliman
Location: Chicago, IL USA

Thanks Rob.

I was told a few days ago that I'd get close to 10 charges on a 55aH battery so it looks like the calculations are close but not exact.

Since my original question (using a 65Ah battery), I was now leaning towards an Optima Yellow or Blue Top 55Ah deep cycle marine battery.

Based on your calculations however, I think I'm going to continue to look for a 65-75Ah battery. I think Optima makes one but it's going to be quite a bit heavier. If I could get 5-6 charges with the 55Ah Optima I'd go for it.

I was also trying to balance capacity vs weight as I was planning to cart this battery from the car to the flying launch area (100+ yard walk).


Dave
07-09-2008 06:23 PM
 
 
Rob_T
Elite Veteran
Location: Tualatin, OR - USA

I'd be really confident of getting 4 charges out of a 55Ah battery. You might get a 5th depending on the efficiency of your charger and how far you discharge your batteries in flight - but if that 5th charge is important to you you might be disappointed.

Whoever told you 10 charges with a 55Ah battery probably didn't realize you're using a 6S lipo, or else didn't know how to take that into account.

By the way have you considered buying more lipos so you don't need to perform as many charges at the field? It will also work out much lighter when you transport everything from the car to the flight line!


Rob
Eco8, Piccolo Fun, Shogun, HB Elite CP, Trex 450XL CDE, Swift
07-09-2008 09:31 PM
 
 
HeliMan Dave
Heliman
Location: Chicago, IL USA

Thanks Rob.

The person that told me that was a tech at FMA Direct. That's where I bought my CellPro Revolectrix 3s 2200mAh and 6s 5300mAh packs (the 3s blow my Thunder Power eXtreme 2200 V2's away with both longer flight times and more punch throughout the discharge) I also told him I'm using their 10s charger.

I assumed he should know.

I'd love to have more than (3) 6s packs but at $342.50 per pack I'd rather recharge than buy more right now.

I've got (6) 3s packs (much less expensive) for the mini-Titan so those are not an issue.

The Optima 55Ah D34M that I'm looking at weighs 44 lbs. If I go with the 75Ah D31M, the weight is 60 lbs which is a little more than I want to carry around every day. Then again I guess I could just leave it in the car.

Do you have any other battery suggestions?


Dave
07-11-2008 04:45 PM
 
 
Rob_T
Elite Veteran
Location: Tualatin, OR - USA

My own field charging solution is a 100Ah marine battery from Wal*Mart. Where I fly it's usually easy to leave the battery by the car - and I need to because that battery is heavy!

I think you'll find a small generator works out at about the same weight as the smaller Optima battery (the Honda EU1000i weighs 33 lbs with enough gas to run 8 hours the way you'll be using it.) But you'll need either a 12V power supply to use the 110V output or a small battery connected to the 12V output of the generator (the generator 12V output is designed as a charger rather than as a 12V power supply). Not a cheap solution either.


Rob
Eco8, Piccolo Fun, Shogun, HB Elite CP, Trex 450XL CDE, Swift
07-11-2008 06:40 PM
 
 
HeliMan Dave
Heliman
Location: Chicago, IL USA

Rob,

That was one of my choices (cheaper marine battery). I guess I've been thinking it would be better to spend a little more on an Optima.

I had a nice Yuasa 12V 65Ah SLA in the back of my Explorer for many years for emergency radio power but it finally wouldn't hold a charge. New ones are $270.00 so I was going with the next best thing.

Maybe I should just go Wal-Mart (or other inexpensive marine) after all?

The 55Ah Optimas are $200.00 (but 175.00 with current rebate) so I can only imagine what the 70Ah ones cost. I'll have to check.

Since it will be kept in my Explorer (and is noisy) I don't really want to go with a generator.


Dave
07-12-2008 06:33 AM
 
 
Rob_T
Elite Veteran
Location: Tualatin, OR - USA

I just weighed my battery - it's 54 lbs in a battery box (to prevent spills). Also it's 115Ah - a little more than I posted earlier. Price when I bought it was about $60, so it's much cheaper than the Optima SLAs. But it will spill acid if you let it!

Optimas are a good product, but you pay a huge premium for having a battery that wont try so hard to make holes in your clothes.


Rob
Eco8, Piccolo Fun, Shogun, HB Elite CP, Trex 450XL CDE, Swift
07-12-2008 07:47 AM
 
 
HeliMan Dave
Heliman
Location: Chicago, IL USA

Thanks Rob.

I definitely don't want a standard battery that has to be kept in a battery box. The wife would rather me spend 3x as much and not have the worry. I will only buy a sealed battery.

They actually have some brand of SLA/marine at Wal-Mart/Kmart for about $90 but I'm not sure what the capacity or weight is.

I was starting to think about a 75Ah Optima but the more I think about it, I really don't need to charge more than 3 5300Mah packs since I always bring my mini-Titan and 6 2200Mah packs for that. My flight times are 9-10 minutes avg. for each heli so that would give me 2 hrs of solid flight for an afternoon.

Maybe I'll just get the 55Ah Optima and be done with it. It's only 41 lbs too.


Dave
07-14-2008 07:09 AM
 
 
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e-Electric Batteries & Chargers > SLA Rechargeable 12V field Battery Advice
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