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Jun 16, 2017, 06:16 AM
Registered User
The Flying Pig's Avatar
Discussion

Field Battery


Need to buy a 12v battery to charge my Lipos at the field - don't want to use my car battery anymore.

I use 6S 3350s and 3S 2200s batteries mostly.

Thinking of something like this:

https://www.batteryclerk.co.uk/batte...a-battery.html

Any thoughts?
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Jun 16, 2017, 06:39 AM
Registered User
JMynes's Avatar
You won't get many charge cycles out of that 18ah battery. You can only use 9ah before it's down to 50%, which is the lower limit for a lead acid battery before damage occurs.
One charge each of the 6s and 3s and you'll be close to done.
Jun 16, 2017, 06:55 AM
I am a nice guy! Really!
As it happens I just did research on SLA batteries. It is not quite as simple as 50%. Actual capacity is greatly dependant on the discharge rate. Take a look through the technical info on PowerSonic batteries. Depending on charge rate you may be pulling somewhere between 6 and 10 amps or maybe a bit more. Capacity at those rates is about 11Ah. Of course that is for PowerSonic. Other cheaper brands may not perform as well.

Another thing to notice is that at higher discharge rates the minimum voltage per cell under load goes down. So you may not even get the derated capacity before your charger calls a timeout due to under voltage. If you want to charge more than 2 or three packs of that size you will need a much larger battery.
Jun 16, 2017, 07:11 AM
Registered User
The Flying Pig's Avatar
Thanks - this is the sort of advice I'm after.

Is a standard car battery then the way to go?
Jun 16, 2017, 07:18 AM
Wanted for breaking Ohm's Law
Dennis Sumner's Avatar
I'd suggest a 35ah AGM for batteries the sizes you use. I just replaced a 33ah AGM last month that was 9 years old. I used a mix of smaller 3s1800-4000, 4s5300, and 6s4400's.

....I do start with charged batteries from home, then charge a couple of times at the field.....so far this has worked for me although my use of 6s4400's is new for me.
Jun 16, 2017, 07:42 AM
Registered User
These things are heavy! You have to keep them charged too. They degrade rapidly if left at a low state of charge.
Jun 16, 2017, 07:53 AM
Wanted for breaking Ohm's Law
Dennis Sumner's Avatar
The 35ah AGM weighs 25 pounds. Not bad to haul in an out of the car. I recharge after every time I go flying with a NOCO Genius 3500 charger. I guess that might have helped me get 9 years out of my old one.....
Jun 16, 2017, 08:31 AM
John,not Zerts.JOHN, NOT Zerts
I use a 24F car battery - that's a lot of amp-hours per dollar. I use a lightweight aluminum hand truck that I had anyway to lug it around.
Keep it pretty much charged, most of the time
Last edited by Zerts; Jun 16, 2017 at 04:44 PM.
Jun 16, 2017, 10:01 AM
Registered User
You should figure out how many watt-hours you need in a day.

I used a 100ah AGM deep cycle for several years. A 100ah deep cycle is good for about ~500 watt hours (<half capacity, reduced voltage under load - worse if you want to charge fast.) Charging one 6S 3.35ah battery will use around 85 watt hours so about 6 recharges. As of a few years ago, my typical plane or helicopter used two of those batteries, so that was 3 flights. So, I would say 100ah is good for small to medium vehicles, but after that you either need multiple (which some people do) or a generator.

As for the weight, when I was running the deep cycle, I just left it in the car about 95% of the time. (A sealed AGM isn't supposed to vent hydrogen when charging but I still left the car open.) The 2000 watt generator weighs less but needs to be moved in and out of the car routinely. The generator also works well for multi-day funflys and non-RC stuff like power failures and running electrical stuff in odd places.
Jun 16, 2017, 10:43 AM
Registered User
After trying Lipo's as a power source for field charging I never went back to using deep cycle marine batteries. Lugging around a 85 pound battery for only 500watt hours doesn't seem like a good trade-off.
Jun 16, 2017, 11:10 AM
Bobbybrown
Quote:
Originally Posted by Dennis Sumner
I'd suggest a 35ah AGM for batteries the sizes you use. I just replaced a 33ah AGM last month that was 9 years old. I used a mix of smaller 3s1800-4000, 4s5300, and 6s4400's.

....I do start with charged batteries from home, then charge a couple of times at the field.....so far this has worked for me although my use of 6s4400's is new for me.
I would couple your setup with a solar charger for the primary battery and never look back. It would charge anything you want all day long.
Jun 16, 2017, 02:22 PM
Registered User
Or convince your club to put in a charging station with car batteries and solar charger. That is what my field has. There are enough stations for everyone to charge at the same time. Just bring your charger and a set of leads!
Jun 16, 2017, 02:31 PM
27 yrs. of Aircraft flying.
epoweredrc's Avatar
I have a 120 AH deep cycle battery and it's been great, I keep a cheap voltage meter hooked up and when it gets down to about 12.2 I will charge it. I hook a line to my truxk and just crank my truck and let it charge it bk up. I charge up to 4000mah 6s for my big heli on it.
Jun 16, 2017, 04:29 PM
Bo Edström, Sweden
Hi,
I have field charged for many years, summer and winter. At first I had wet lead acid Pb 12 volt batteries around 70-80 Ah as source fo my chargers. In last 4 years I have used AGM 12 volt batteries and they are much better (but more expensive). I have four 95 Ah AGM batteries and that is what I need if I fly from morning to evening charging my 10 cell LiPo pack (that is actaually 5 cell x 2 in series). 70-80 Ah AGM battery (for deep discharge, not start battery) would probably be OK for You if You do not mind one such battery weight around 20 Kg /44 lbs.
A generator coluld also be an alternative but some are rather expensive like Yamaha and Honda brand. I have thought about a Yamaha EF2000iSv2 myself but it is a lot of money and the gas bill will be rather high with my level of usage so I continue with AGM batteries as power source little longer.

/Bo
Jun 16, 2017, 04:50 PM
Registered User
Nice pattern ship!


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