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Author Topic: small battery issues  (Read 3286 times)

bill stafford

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small battery issues
« on: June 16, 2015, 08:06:18 AM »

hello again, I'm in trouble ,and would like an opinion,
i used eneloop batterys to power a small garnock+guardsman, the battery wont drive the model , yet on the multimeter seems almost OK,there doesn't seem to be any "guts" in the battery, mA ??
has any one had similar issues, w long life NiMh??
is there a way to test capacity in small rechargeable ?? , multi meter isn't helping much,as voltage seems ok , in all cells both models are not happy, looking at repower w 123 cells , 1500 NiMh

bill s
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boat captain

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Re: small battery issues
« Reply #1 on: June 16, 2015, 09:02:55 AM »

Hi

Check your battery voltage with your meter then go across the battery terminals with your motor running with no load on it if there is a significant drop in voltage the battery is useless.
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JimG

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Re: small battery issues
« Reply #2 on: June 16, 2015, 11:13:17 AM »

The problem with small NiMhs (AAA and AA) is that while they may have a high capacity they are not capable of providing any decent current. Connect them to a low current drain  they are OK but when you take too much current the voltage drops under load. You will be better off using the 123 cells as they can provide the current needed.

Jim
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SteveB66

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Re: small battery issues
« Reply #3 on: June 16, 2015, 07:42:34 PM »

Or buy a little Lipo if you want 3.7 or 7.4 volts or even LiFe if you want around 6 volts. Many sizes and they are light to. You won't need to change speed control either if you use a lipo alarm to tell you when the batteries are getting low.
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bill stafford

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Re: small battery issues
« Reply #4 on: June 18, 2015, 12:49:55 AM »

thanks gents , for your help.
I have being talking to the model plane guys ,seems there is a battery checker ,to test various batteries , on load,and the eneloops are not reliable for drive batteries
not keen on using lipos on small models ,i have done this ,and the 11.1V battery burned out a 12V controller, seems a special s/c is needed, not certain why, as voltage was with-in specs ??
 thinking of trying LiFE or 123 cells
thanks bill s
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JimG

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Re: small battery issues
« Reply #5 on: June 18, 2015, 11:22:35 AM »

not keen on using lipos on small models ,i have done this ,and the 11.1V battery burned out a 12V controller, seems a special s/c is needed, not certain why, as voltage was with-in specs ??
 
thanks bill s

It could be due to the 11.1V lipo is actually 12.6V when fully charged, if the 12V esc is marginal on tolerance the extra voltage might be too much.

Jim
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inertia

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Re: small battery issues
« Reply #6 on: June 18, 2015, 12:00:27 PM »

It's usually too much current which damages speed controllers rather than too much voltage - especially where the rating is 12v. A fully charged 12v SLA is around 13.5v but they are fine with 12v ESCs.
You don't need a special ESC for operating with LiPo packs. A low-voltage alarm has a very piercing squeal and can be purchased for around three pounds. It plugs into the balance lead of a LiPo pack. http://www.componentshop.co.uk/led-battery-status-indicator-alarm-for-1s-to-3s-3-7-11-1v.html  You can also buy one that cuts off the power to the motor if the voltage gets too low. http://www.modelsport.co.uk/gv-models-li-protector-cut-off-2-4-cells/rc-car-products/31336
I use one of the CompShop alarms on a 3S LiPo in my 1/16 scale Huntsman (23" long) with a brushless outrunner motor and 18A ESC - no problems so far.
DM
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bill stafford

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Re: small battery issues
« Reply #7 on: June 20, 2015, 10:54:22 AM »

hello DM,
 you know more about it than me , but, how can a low battery alarm help w stopping a normal s/c from destroying itself ,after all , in my situation, it was a over supply of current , not voltage ,that seemed  to be the problem, as it was in the first stage of the model run, w the battery freshly charged.
as a first time user of lipos , all seemed fine ,battery was high in voltage , but under load, i thought it would drop back to 11.1 V+speed control -also the speed control was not specified for lipos , but I was going on the voltage,as i now know ,lipos require a certain type of s/c  cheers bill s
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inertia

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Re: small battery issues
« Reply #8 on: June 20, 2015, 11:54:50 AM »

Bill
Sorry, but LiPo batteries do NOT require a special type of speed controller. What they do need is some way of telling you that they are getting low in voltage, because if that happens then they can do nasty, hot, smelly and smoky things to themselves and your model.
There are three ways of minimising this risk;
1. A speed controller which automatically senses the pack voltage and first reduces the power to the motor (to enable you to get the model back to shore), then cuts it off altogether if the voltage drops any further.
2. A small alarm which connects to the battery pack and sounds a loud whistle when the battery pack gets down to a certain level.
3. A low-voltage alarm like this doesn't reduce or switch the power off unless it's a special type e.g. http://www.elitemodelsonline.co.uk/Products/Electronics/Electric-Flight-Accessories/6346-/LIPO-BATTERY-PROTECTOR-2-4-CELLS Note that neither 2 nor 3 requires the use of a special speed controller.
A low-voltage alarm won't protect a speed controller from damage due to excessive current - I didn't say it would. I wanted to correct your assumption that a 'special' type of ESC is required when using LiPo batteries. The cause of your ESC's demise was more likely a fault in the installation or within the speed controller itself. In that event the type of battery connected to the speed controller at the time isn't material.
DM
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Netleyned

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Re: small battery issues
« Reply #9 on: June 20, 2015, 12:56:32 PM »

There is so much myth about lipos.
You hear it at the lake.
"It'll go faster with a Lipo"
It's battery chemistry
A motor will run at the same speed no matter what batttery
is used if the voltage is the same unless the current draw
needs a battery capable of delivering high current.


Ned
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inertia

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Re: small battery issues
« Reply #10 on: June 20, 2015, 01:25:47 PM »

Spot on, Ned - except "myth" wasn't quite the word I would have chosen!  %)

Like most things, the loudest noises seem to come from those who actually have little else but their opinions and prejudices to share (hence Bill believing what he did about needing a special ESC).
From initially being very wary of LiPo batteries myself - largely by apocryphal tales of frequent disasters with them - I've researched the correct way of treating them from those who really do know the subject; bought and used some packs of them for a while, and I'm now a convert. They do have limitations i.e. they won't take as many charge/discharge cycles as NiMH cells before they are exhausted and they require more care and attention to charging and discharging them, but they do suit the sort of small models which I prefer these days (24" - 30" long).

I'm even warming towards brushless motors, but that's another story.

Dave M
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Peter Fitness

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Re: small battery issues
« Reply #11 on: June 20, 2015, 11:31:17 PM »

I'm even warming towards brushless motors, but that's another story.

Dave M


Who said a leopard can't change its spots  {-)


I've been reluctant to try LiPos, for the same reasons as Dave mentioned, such as horror stories of spontaneous combustion or explosions. Maybe I'll have to have a rethink.


Peter.
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bill stafford

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Re: small battery issues
« Reply #12 on: June 21, 2015, 07:10:47 AM »

gday gents ,
 i do use lipos, in a small, new way , to drive my foam plane trainer, so i do know a little about them ,but far from a large experience.  I suspect some of my issues come from motor drawing more Amps than the controller could handle , I didnt check that , rather only voltage ,and from memory , it was close to 12V, as battery was a 11.1V, I thought I was good
for the record, lipo` s are safe too use,if in doubt, buy a good charger , both mine charge the battery, and the battery is almost cold to the touch,  very safe useage, but they are capable of delivering high current.
 In the past , I have always treated this part of the circuit, as a power supply, in the future i will also,  but I will be more careful  checking both amps+voltage supply, to motor .
 but do we need a lipo s/c ??  may be we do,  when it comes to the older design s/c ?????
to solve my small battery issues,  I have ordered some 123 NiMh cells , looking at LiFe cells,as a AA cells produces 3.3V
regards and thanks bill s
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SteveB66

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Re: small battery issues
« Reply #13 on: June 21, 2015, 09:47:56 AM »

Mtronics do a lipo compatible speed controller with the appropriate cut of to protect you lipos.
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inertia

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Re: small battery issues
« Reply #14 on: June 21, 2015, 10:38:38 AM »

but do we need a lipo s/c ??  may be we do,  when it comes to the older design s/c ?????

At the risk of repeating what's been said already, a "LiPo" ESC is ideal and so most (if not all) brushless ESCs appear to have programmable low-voltage cut-off.
For brushed motors, however, the choice seems negligible. I know of the MTroniks Tio range, and the Microgyros FR40 also has had low-voltage cut-off (I gather that Mike has stopped producing these - regrettably) but I'm not aware of any other type. There are probably a few on the Chinese warehouse websites but I prefer to buy UK if I can.
If you have an 'older design' then there's no choice but to fit a supplementary device to monitor/cutoff the voltage - or risk it.
DM
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