After some details of SLA weights and stuff

[daveimi]

That's great thanks terry. How many amp-hours do people get through in a fight? I only have 24V 10A wheel chair motors so can't see me using that much lol.

[geeza]

Typically 2.5 - 3Ah per fight, but that is with Bosch 750s

[daveimi]

Oh ok that's cool. So if someone had a couple of 22ahr batteries cabled to give 44ahr in theory you'd get through a whole even without recharging?

Has anyone tried something like 5000ahr NIMH packs in a heavy?

[blazerbotics]

You will find that current delivery is more the issue, rather than the capacity, hence the reason for paralleling up packs.

[geeza]

Mike used NiMh packs in Pressure, they are not quite as good as Nicads in terms of current delivery (in general). Stick with SLAs to start with unless you feel confident (and have the money) for A123 or Lipo batteries. Also think you will struggle to find 44Ah SLAs. I would suggest buying two sets of smaller 10-16Ah batteries, then put all of them in the robot to boost the weight.

[maddox10]

3ah in 3 minutes means a continue draw of 60amps. But fights ain't a continous draw, it's peakload after peakload.

And sla's are very inefficient in that kind application.
That's why a robot that blows up 9ah sla batteries in about every fight can perfectly work fine on 5000mAh 30c LiPo.
Also the reason why "historical" 12 to 17ah sla of normal quality was used in heavies on tv.

I know where my money goes to.

[daveimi]

Ok I understand. I knew you all would know if it was doable, and I understand now why you all have a load of smaller packs making up the voltage as opposed to a single huge battery.

I had wondered this, in particular with John Bell's Titan. When we were fighting at Doncaster we were wandering about looking at the heavies, and Titan has rows and rows of tiny SLA's along the back corners. I now can guess that this is because of the huge LEM?PERM? he has on the axe and the amount of current it must suddenly pull from the batteries upon firing.

The bank of smaller batteries gives more "surface area" to pull current from.

This is why I like being on here, I have a read through most days but there's so much collective knowledge it's frightening. I've literally built robots so far based on asking questions like this.

[leorcc]

Titan uses LiFEPO4 packs, since John moved away from Nicads. Bullfrog also uses those packs, and we on average get 2Ah to 2,5Ah tops out of them in one fight. Recharging takes less than 15 minutes, so last event we did 2 fights per show with ease.

[mattsdragons]

Little thing about titan, only 2 of those packs are for drive, the rest is the weapon

[Revsmin]

More packs for the weapon now, it's up to 40v

[daveimi]

Ok following on from this I'm ready to get cooking with wiring!

Are these suitable

http://www.componentshop.co.uk/12v-9...d-battery.html

And will this charger charge them ok?

http://www.componentshop.co.uk/4000m...ries-3313.html

[blazerbotics]

They are a suitable type, but you will probably struggle to get any major current draw out of them, might be pushing it close on capacity as well. I would go more for this size http://www.componentshop.co.uk/12v-2...d-battery.html that's the most common size used.

[daveimi]

That's fab thanks, gonna order them now. Does the charger look alright? Obviously I spose the beefier the charger the faster it'll charge.

[geeza]

That charger says it will take 12 hours to charge the batteries Alan suggests.

I assume you will get 2 chargers?

[daveimi]

Just ordered the 9ahr batteries and charger as in the original post. I'm only running wheel chair motors so think I'll be alright with those. If they drain really quick I will buy bigger packs, but only have £50 on batteries and charger at the minute.

It was mostly just to know if they were the right chemistry. If I move on to Mags or something similar in the future I'm well aware I will need more battery capacity.