Battery help.

[Chris230291]

Hello. I've been looking at what might be the most cost effective way to provide power. I was wondering if i used cells that are 4.5v each (for example), do i need a special charger to charge a pack of these (a pack i will build) or does the voltage not make a difference? Obviously if the batteries are Li-Ion, Ni-Mh, Ni-Cad etc i will need the appropriate charger, but does each cell voltage effect anything at all?

Cheers,
Chris.

[typhoon_driver]

Are you talking about mixing battery chemistry? If so, then don't. You need a charger that can charge the chemistry of battery that you have at the cell count you have. I have yet to find any cells that give a voltage of 4.5V

[Chris230291]

You misunderstood. No mixing of chemistry. I made the voltage up.
What i'm saying is does it matter if individual cell voltage is greater than the "standard" 1.2V as far as charging is concerned?

Cheers,
Chris.

[Max]

Every single nimh cell is 1.2v nominal, every single nicd cell is 1.2v nominal, every single lithium polymer cell is 3.7v nominal, every single sla cell is 6v nominal. As long as your charger can charge and is set to the cell chemistry you are using it will charge it. You can't get cells that are a different nominal voltage that the standard as far as I am aware.

[Chris230291]

Cheers Max thats exactly what i wanted to hear!
By the way, you can get obscure voltages but they tend to be made to order, or so i've been told
I was just curious about charging them.

So any Ni-Mh charger will charge any Ni-Mh pack, but depending on how good the charger is will determine the charge time?

Can anyone recommend any decent chargers? Ideally a multi-chemistry one, but Li-Ion is the priority at the moment as i imagine the multi-chemistry ones cost a fortune?

Thank's again.

[Max]

Your not allowed to us lithium ion. The only lithium chemistry allowed is lithium polymer (LiPo) and lithium iron (LiFe). Most chargers these days are multi-chargers especially ones that charge lipos. The quality of carver makes relatively little difference to the charge time, most packs have a limit to charge rate which even cheap chargers can achieve.
A lot of people use chargers from hobbyking or giantshark I think- some thing like IMAX-B6 from memory but can't really remember as I've never bought one.

[Chris230291]

How come i cant use Lithium Ion? Surely they're safer than Lithium Polymer? Thanks for telling me though!

Arh well thats good about the chargers. Are you referring to these ones?

http://www.ebay.co.uk/itm/iMAX-B6-AC...item43bdf44715

I was already looking at these but just assumed them to be cheap Chinese crap. haha

Chris.

[Chris230291]

Now having had a proper look at the rules and at different battery types, how would the event organisers know which type of batteries i'm using if i build the packs up myself?

I assumed that li-ion and li-iron were the same thing but i now know the difference. It looks like Li-Po is the way to go now. It's going to cost me a lot more though! *angry face*

[blazerbotics]

What do you mean by "build the packs up myself" ?

[Chris230291]

Weld/wire the cells together myself and apply my own heat shrink. No visible markings to indicate what i'm using.

It's starting to look like the majority of the cost is going to be on batteries. Is this the case for most builders?

Whats the cheapest way of getting 36V that will last long enough? I have 4 motors here that each draw 60+ Amps when stalled. They weigh 1.1KG (ish) each so i need to watch my weight because the chassis wont be light either.

[terry]

Lipos are cheap what's wrong with using them, I assume its for a fw at only 60amp stall per motor, its what nearly everyone else uses. 36v is a high voltage is that the voltage of the motors?

[Chris230291]

Well i must admit my math skills suck. I was under the impression that the regular model kind won't cut it?
The motors are 24v but i'd like to run them at 36v if i can afford to in terms of cost and weight.

Would you mind linking me to something you think is suitable so i can get an idea of what will work?

Thanks,
Chris.

[Ellis]

The motors scooter motors, by any chance?

[Chris230291]

Hello Ellis. If i google "scooter motor" the image results look similar, so i guess so. Why, does that matter?

Chris.

[Ellis]

They probably have a sticker/plate on them giving some stats, are you able to see a wattage rating? It'll look something like 150w, or 300w, etc. If not, find the closest google image you can, it should be possible to gauge within a bit what size motors you have.

I ask because chances are very high that just two in the machine will be plenty of power. Even at 24v. Check out this build to get an idea what two, at nominal voltage, will get you: http://www.fightingrobots.co.uk/thre...am-gas-diary-s