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Author Topic: Battery Options  (Read 1136 times)

Geoff

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Battery Options
« on: May 04, 2017, 02:00:02 PM »

I am currently using five 12 volt 7 amp hour lead acid batteries in my model of Iron Duke for the gunnery power supply. They are the standard "brick" type batteries.


My question is what other alternatives are there that I could use not exceeding the same size or weight but ideally with significantly more amp hour capacity.


Thanks


Geoff
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canabus

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Re: Battery Options
« Reply #1 on: May 04, 2017, 02:24:09 PM »

Hi Geoff
What about Lipo batteries e.g. Turnigy 5800mah 25C 3S(11.1 volts)  fully charged 12.6 volts weight 475 grams 149x49x30.
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Geoff

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Re: Battery Options
« Reply #2 on: May 04, 2017, 02:25:50 PM »

I'd thought about those but that only gives me 5.8 amps as opposed to 7 amps to play with.

Cheers

Geoff
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canabus

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Re: Battery Options
« Reply #3 on: May 04, 2017, 02:45:51 PM »

Hi Geoff
I only used that size as a sample because I have one, larger ones are available and higher C rating.
I also have two 4S 5800 mah (14.8 volt) ones in a setup for 11600 mah with 60C rating.
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T33cno

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Re: Battery Options
« Reply #4 on: May 04, 2017, 09:14:20 PM »

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Paul2407

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Re: Battery Options
« Reply #5 on: May 05, 2017, 07:39:32 AM »

Also worth taking into account the weight difference between Lipo's and Lead acid batteries especially if you use them for ballast you will need at least 8-10 2s lipo's maybe more! to match the weight of a 12v 7amp battery
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Geoff

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Re: Battery Options
« Reply #6 on: May 05, 2017, 08:33:25 AM »

Thank you for the replies which appreciated. Weight is an issue so I can't use the 12 v 9amphr lead acid as they are just a bit heavier. At the moment ID has five 12 volt 7amphr (for the guns - one separate per turret) plus three 6v 7amphr + one 6v 3.5amphr (for the main propulsion in parallel) + one 6v 3.5amphr for the radio so ten batteries all in. No ballast is needed!!

I'm trying to see if I can get higher capacity for less weight so I can extend the gun sequence. Lipo's certainly seem a possible solution (ignoring cost) but we need to consider for the guns maximum current consumption is a little less than 10 amps.

If I switch the guns on and just keep firing I can probably get about 500 shots in all but in practice I tend to fire about 10/12 salvos and then rest. The rest period means the thermistors cool down to ambient so when I switch on again current consumption starts from ambient so overall I use more current in three or for sessions than I would in a single session which is why I seem to be peaking at about 60 salvos all in rather than 100 hence the need for increased battery capacity.

Cheers

Geoff

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canabus

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Re: Battery Options
« Reply #7 on: May 05, 2017, 08:37:15 AM »

Hi Geoff

The SLA 12v 7AH I have are L=151mm, W=65mm and H (without the terminals) 94mm.
Weight 2441 grams.
So two 3S 5800mah Lipo's equals about the same size, but, with 11600MAH.
Lipo's deliver more power than SLA batteries that is why they are used on brushless motors.
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malcolmfrary

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Re: Battery Options
« Reply #8 on: May 05, 2017, 08:47:59 AM »

For the same capacity, anything other than Lead acid will weigh less.  Sadly, it is likely to cost more for the same weight.  Even the same capacity will probably cost more.
NiMH batteries are available in a wide range of capacities and are fairly simple to look after (probably easier than lead).  For the same weight, you get quite a bit more capacity.
Lithium cost a lot when you move into high capacities, and do need the right charging and monitoring.  For the same weight, you get a lot more capacity.
I'm not 100% sure, but 60 salvos was probably more than the original could manage anyway.
Thermistors?  What are they looking after/sensing/protecting?
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Geoff

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Re: Battery Options
« Reply #9 on: May 05, 2017, 09:05:31 AM »

Yes but what about connecting two Lipo packs in parallel to get the capacity - is it safe and what are the complications? I would also be using Lipos until they are nearly exhausted (well unable to deliver the current needed) so I have some concerns at possible battery damage/longevity. Experience has taught me that the whilst the thermistors are all the same in practice there are slight differences in current consumption which is why I use separate batteries for each turret to preclude one thermistor dominating and dragging the other down. Same issues with two motors - one will dominate and in the end both can be dragged down.


Cheers

Geoff
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Geoff

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Re: Battery Options
« Reply #10 on: May 05, 2017, 09:06:52 AM »

The thermistors are the heating elements for ID's gunnery system - they run at 230 centigrade and are self regulating.

Cheers

Geoff
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malcolmfrary

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Re: Battery Options
« Reply #11 on: May 05, 2017, 08:55:29 PM »

Quote
I would also be using Lipos until they are nearly exhausted
Not unless you like replacing them often you won't.  That is what the alarm is for, to discourage or better yet prevent discharging beyond the point where damage will happen.  If it was a type that ceased supply at the low battery point, that would be the "no more bullets" (thank you Elmer Fudd) point.
The manufacturers generally produce high capacity batteries by connecting banks in parallel.  If they are all at the same voltage at the time of connection, they just act like one big battery without any undue drama at the time of connection.  Afterwards, they continue to act as one unit.  If you are using a laptop, the proof of concept is in front of you.
I still think that NiMH are better behaved and rather less fragile, even if their capacity is lower per unit of weight.
Never thought of using thermistors as heating elements -  I only ever came across them when used to suddenly change from high to low resistance when they were presented with a high voltage where the sudden drop in resistance on heating, and the subsequent increase on cooling, was of great benefit.
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