Grampian Radio Car Club

Hi keiran

This is copyed straight out of an email that keith sent me



The C rating (ie. 25C, 30C etc) is the continuous discharge rating of a lipo
and really indicates how much work the battery can do. So a pack rated at 25C
can effectively deliver its capacity (eg. 2500mah) 25 times faster. A pack
rated at 20C can effectively deliver its capacity (eg. 2500mah) 20 times faster.

Another more complicated way of looking at it is current draw and what the
battery is able of pushing out. Obviously a super fast turn motor needs a lot
more current (power) to run than a stock motor - this is the reason any pack of
cells will work longer with a 19t motor than they will with a 10T motor. So,
back to my point, you can rate the current draw in the previous examples as:

25c x (2500/1000) = 62.5Amps
20c x (2500/1000) = 50Amps

The reason I am dividing the mah rating by 1000 is that the mah figure is in
milliamps and we need to convert into into amps. For example 2500/1000 = 2.5A
so the pack could deliver 2.5amps over one hour (or 60 minutes). If you charged
it and it was completely flat at 2.5A then it would take 60 minutes to charge
too!

If you were drawing 50Amps out of a 20C pack then obviously it would not last
60 minutes, it would just last 3 minutes!

These are all just examples really but hopefully it illustrates what you need
depending on what you run.

In my experience, something like a 3700mah pack will last over 10 minutes with
a 19T or 10.5 brushless motor.

For serious modified rating then a 3700mah pack may only last for one 5 minute
run.

Be very aware of the huge figures that some companies are quoting though.
There's a lot of 40C packs that are really 35C and a lot of 35C packs that
are really 30C packs!


Hope that helps you a bit or anyone else interested
I also like Darren have 2 demon 5000mah 35c packs

Good old Keith, that's what I was going to say!

Thanks for the offers guys, unfortunately though I've not got the charger in my hands yet. I keep forgetting to change my delivery address on eBay so it ends up going to my Mums house!! I might try get the charger before the racing on Sunday though, so if your not using that Li-po Chris I wouldn't mind giving it a bash! I should have my new ESC tomorrow, if I don't I'll be straight on the phone cause they charged me £6 postage!! If I for some reason don't get it for the weekend, I'll stick with brushed as it's not really much of a disadvantage indoors and I'm too lazy to be soldering!

Cheers Gareth, it's all a bit like the mAh with Ni-MHs!! Don't matter how much goes in, it's how much comes out.

Hi Kieran,
Nice to see that you are thinking of coming over to Li-po, I am sure you will notice a difference in the ease of use between Li-po and NIMH cells.

I am only using one Demon 5000MAH 40C lipo pack. I find that there is just enough time to recharge at inverurie, and for outdoor rounds, there is ample time. I am also using a Pulsar 3 and it charges this cell fine. I regularly check the voltages of the 2 cells to make sure they are the same and I haven't had to balance charge it yet (Had it since the Benarty round of the SRCA last year).

Keep an eye on the Rc Racechat forum, there seems to be Li-po packs for sale on a regular basis, last week a guy was selling the same lipo I have for around £55, and it had only been used a few times.

I am hoping to come along on sunday, any questions then let me know!

Marc

K,

WIll charge that lipo for you and bring it along.

Cheers Chris, although not sure I'm gonna be able to use it now! My speedo turned up today by courier... so of course I was at work and the kind UPS man left it with a neighbour who obviously told him he was going away till Sunday cause he wrote it on the ticket. Why he couldn't have come up the stairs and given to my neighbour across the hall who is always in... I don't know! Not like it was sent next day delivery for a reason...

Can you not go collect it today at the couriers?

No unfortuantley my neighbor has it who is away till Sunday. Left a note on their door, hoping they'll be back in the morning.

ah sorry I missunderstood your first post. I have large feet and a good pair of boots if you need :>

Got some tape today so no need for anyone else to bring any

Yus! Got a demon 5000, 35c LiPo off eBay. Should arrive on Friday, need to get some scales and sort the weight out now.