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Battery

Field charging

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Tony Hobson24/07/2019 10:10:43
17 forum posts

Hi All,

I'm thinking of buying a 12v battery for on field charging, anyone got any suggestions on best price, best supplier etc. Thanks in advance,

Tony

Alan Gorham_24/07/2019 10:19:20
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1014 forum posts
123 photos

I have used 12V 110Ah leisure batteries (the same as I use in my caravan). Be aware that this battery is physically big and heavy and is a pain in the back to move unless you make a trolley or something (more guff to take flying!).

I have used such a battery to charge 5 and 6S Lipos for an entire weekends flying. Usually the leisure battery needs replacing after a year or two depending on how much abuse you give it.

You should consider the size (number of cells and capacity) of the batteries you wish to charge as even a leisure battery which is designed to be deep discharged will only be able to do a finite number of charges in one session before it needs charging.

I have either used my local caravan accessory shop or online here has an amazing choice of batteries:

**LINK**

If you are charging smaller packs such as 3s 2200 Lipos then you may be able to use a smaller battery, but consider the economics of just buying more Lipos and charging them all at home instead too....

Robin Etherton24/07/2019 10:48:00
271 forum posts
41 photos

Hi

Up to 4s I use a 12v 18 amp power sonic gel battery.

Manageable in size and plenty of power.

Google 12v 18amp to find one.

Robin

Shaun Walsh24/07/2019 11:08:13
195 forum posts
13 photos

These people are very good for batteries.

**LINK**

They also sell at a lower price on ebay!

**LINK**

It was £5 cheaper to buy a new battery for my classic VW from them on ebay than it was to drive a few miles and pick it up from the store. They sent it by courier, next day delivery.

Dickw24/07/2019 13:11:17
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479 forum posts
76 photos

Going in a sightly different direction on 12v batteries - I also used Leisure batteries in 110 Ah or 80 Ah sizes for many years, but got fed up with having to replace them every couple of years.

About 7 years ago I invested in a 4s2p LifeP04 battery built myself using 15 Ah cells so giving me 12v 30 Ah. Because of the different discharge characteristics of the Life cells I found I got more out of them at the field than I ever did out of an 80 Ah Leisure battery, and they are still going strong unlike any of the Leisure batteries I used.

I got the cells, connectors, etc. from here. Not cheap initially, but they have saved me money in the long run.

The other advantage is they are a lot less weight, so the pack is built into my model box as per the photo.

charging batt.jpg

Dick

Shaun Walsh24/07/2019 13:18:36
195 forum posts
13 photos

Applying lateral thinking how about one of these? devil

**LINK**

Edited By Shaun Walsh on 24/07/2019 13:18:51

Martin Harris24/07/2019 13:21:39
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8868 forum posts
221 photos

I'd prefer to cut out the middle man and just use the engine to turn the prop!

Shaun Walsh24/07/2019 14:04:43
195 forum posts
13 photos
Posted by Martin Harris on 24/07/2019 13:21:39:

I'd prefer to cut out the middle man and just use the engine to turn the prop!

But what if the flying field is silent flight only. 😁

Martin Harris24/07/2019 14:22:06
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8868 forum posts
221 photos

I wouldn't be there...wink

Mind you, it does raise the point about defining silent flight. When the term started to be applied to EP models, brushless motors powered by NiCds had barely enough power to turn the propellers of the average model and they struggled to waft around for more than a few minutes.

Contrast that with the present day when 50cc equivalent motors whirling massive props, EDFs, pushers and high revving electric models are common. It's arguable that on a typical club day, the noisiest (certainly by perception) models are likely to be electric ones now that 2 strokes are becoming less common.

Perhaps one day I'll do some noise tests on electric models...might be interesting!

Shaun Walsh24/07/2019 14:40:18
195 forum posts
13 photos
Posted by Martin Harris on 24/07/2019 14:22:06:

I wouldn't be there...wink

Mind you, it does raise the point about defining silent flight. When the term started to be applied to EP models, brushless motors powered by NiCds had barely enough power to turn the propellers of the average model and they struggled to waft around for more than a few minutes.

Contrast that with the present day when 50cc equivalent motors whirling massive props, EDFs, pushers and high revving electric models are common. It's arguable that on a typical club day, the noisiest (certainly by perception) models are likely to be electric ones now that 2 strokes are becoming less common.

Perhaps one day I'll do some noise tests on electric models...might be interesting!

A valid point Martin, it would be interesting to compare the noise output from the same model correctly propped for a 4S IC motor and an electric motor. I must admit that I had a problem with an electric model recently that necessitated the replacement of the motor as the original was running about 0.5mm out of true when you looked at the end of the prop shaft, the reason I noticed was because it was somewhat noisier than normal. New motor and all is back to normal again. The days when you could blat around the sky with a K&B 40F running with an open venturi "silencer" are long gone.

Allan Bennett24/07/2019 15:11:48
1555 forum posts
39 photos

At our club we have one flying site which used to be designated as 'silent' due to the proximity of housing. It was therefore used for bungee-launched gliders only. Maybe 20 years ago members gradually started flying electric gliders there, subject to Committee's subjective approval on a model by model basis. This worked okay, but more recently members thought it would be okay to fly other electric-powered models there, so the Committee was tasked with determining what dBA figure represents 'silent' in the context of this particular site. After a few test flights and noise-meter tests it was determined that 72dBA (under the same conditions as the standard 82dBA test) would be acceptable. This level can be met by models such as Twinstar, Bixler, foamy AcroWot, etc., and has caused no problems with our neighbours.

SIMON CRAGG24/07/2019 16:04:36
473 forum posts
15 photos

I have never bought a new field battery in over 40 years.

Either got one from the dump for nothing (some are ditched way before they need to be), or from the scrapyard for £25.00 a time.

Dickw24/07/2019 17:25:54
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479 forum posts
76 photos

There is the option of using solar panels to keep a small 12v battery topped up while charging.

Dick

dsc_0435.jpg

Foxfan24/07/2019 18:15:54
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836 forum posts
6 photos

We had 4 brand new 110 Amp deep cycle leisure batteries on our historic narrow boat, 3 for the domestic systems and 1 for the engine start. The whole system was monitored by an English hi-tech. charge monitoring system which gave us a read out for consumption, battery state, charge rate, etc. They lasted a week more than the 3 year warranty! Then just died. Flat as a witch's doo-dahs one day. Fiver each from the scrap man.

I'd find an alternative!

Martin

Peter Jenkins24/07/2019 23:42:05
1279 forum posts
132 photos

My experience with field charging with a 110 Ah leisure battery was not good. I use a 2 x 5S 5000 mah packs connected as 10S but charged as 2 x 5S so 10000 mah. The battery, new and fully charged managed not quite 3 charges of the 2 x 5S packs. As mentioned above, the battery is very heavy and after several experiences of not quite 3 charges in the field before the battery was down to just under 12 volts. I decided that the cost of a new Leisure Battery was balanced by buying 3 more flight packs. I now take 6 flight packs with me and bring them home to charge them. I should explain that I fly F3A aerobatics so flying 6 schedules in a session, usually half a day, is about all I can cope with.

A genny was something I also considered but then you have to add in the weight of the genny and the space needed in the car for it plus the need to carry petroil (OK you probably don't need to take any with you provided you remember to fill the tank before leaving home).

Steve J25/07/2019 09:38:46
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1560 forum posts
47 photos
Posted by Dickw on 24/07/2019 13:11:17:

I invested in a 4s2p LifeP04 battery built myself using 15 Ah cells so giving me 12v 30 Ah.

I know somebody who does something similar. He has a plastic toolbox with a bank of cheap 10C lithium batteries (I can't remember if they are LiPo or LiFe) in it which he uses to charge his flight batteries.

Steve

Cuban825/07/2019 10:14:12
2754 forum posts
13 photos

Can't say that I was overly impressed with a 'Leisure Battery' that I bought a few years ago for field charging. I looked after it i.e. didn't abuse it in terms of discharge current or discharged terminal voltage but after a year of moderate use it's performance was noticeably down on when it was new. Not a cheapy, cost a tad under a hundred quid. Wound up using it in the caravan for a few more years where it led a much easier life and was perfectly adequate running the lights and water pump etc - so not totally wasted. IIRC it had a claimed capacity of 90Ah and a cranking current of over 200A.

Perhaps I was just unlucky, but to lose the equivallent of half of its capacity after such a short time of not particularly hard use wasn't brilliant.

On the solar panel idea - not convinced that a panel would keep a battery that well charged during a flying session, if that is what is being suggested. Even quite expensive ones are only able to deliver milliamps (tens or a few hundreds) when in full sunshine. Depends on what you have in terms of size and efficiency of course.

For an afternoon's flying with say four 1500 3S and a couple of 3000 6S, I haven't had any problem charging from my car battery, but I do monitor it with a seperate meter rather than relying on the charger's input voltage warning. Did push it once (as you do) and got a low voltage warning on the dash when I was ready to go home, but the car tirned over and started as normal. Obviously not an option if you're going to a fly-in or similar for a few days though.

Alan Gorham_25/07/2019 10:36:34
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1014 forum posts
123 photos

Beg to differ on the charging current that you can expect from a solar panel. I used to design LED based road signs and many were off-grid installations that used a battery and solar panel. We used to use 30W panels a lot and could easily achieve over 1A charging current on a partially cloudy day.

I'd take a guess that the panel Dick showed was around 50W and their peak current is around 3A in full sun. lower that to 2A for a days flying and that allows you to take 10A/h out to charge your model's batteries (disregarding cabling losses etc).

I'm slightly curious that the leisure battery you bought had a "cranking current" rating. That sounds more like a car battery to me which are useless at deep discharge so no wonder it went off...

Dickw25/07/2019 10:45:54
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479 forum posts
76 photos
Posted by Cuban8 on 25/07/2019 10:14:12:

Can't say that I was overly impressed with a 'Leisure Battery' that I bought a few years ago for field charging. ...................................................................

On the solar panel idea - not convinced that a panel would keep a battery that well charged during a flying session, if that is what is being suggested. Even quite expensive ones are only able to deliver milliamps (tens or a few hundreds) when in full sunshine. Depends on what you have in terms of size and efficiency of course.

For an afternoon's flying with say four 1500 3S and a couple of 3000 6S, I haven't had any problem charging from my car battery, ...................................... Obviously not an option if you're going to a fly-in or similar for a few days though.

So far that is a fair number of us not impressed with Leisure batteries. I did find that I got on better with an ordinary car battery bought from Halfords - still heavy though hence my move to lithium which gave better performance for less weight.

Not sure what size solar panels you are referring to regarding your quoted performance figures but mine, shown in the photo above, always give me around an amp even on a dull cloudy day and 5 or 6 amps if the sun comes out. Last sunday they put 14.5 Ah into my battery during a day of mixed cloud and sun. The attached data log shows one of my initial tests with the panels last year - a typical dull cloudy day out with a total of about 7.5 Ah output. They certainly work for me, and if 7.5Ah doesn't sound much don't forget that is in addition to my 30Ah battery capacity.

Dick

20180818 f5b practice day notes.jpg

Outrunner25/07/2019 11:50:12
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40 forum posts
2 photos

Back in the days when used to field charge (nicads) I used to use old car batteries, when they ran out of puff down the dump they went, then onto the next ex car battery. These days I take a bunch of charged lipo''s and only bench charge.

Phil.

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