Voltages

[widow_twanky]

The latest rules say that the maximum dc voltages is 75v but limit the size of a battery pack to a 12s lipo. Is it within the rules to put two 10s lipo's in series to achieve the max 72v?

Andy

[typhoon_driver]

I believe that the 75v limit as this is the limit for low voltage applications as far as the regulatory bodies are concerned. And no that wouldn't be legit. A 10s pack can happily have 42v or thereabouts when fully charged so you would only really be able to go to 15 or 16s.

Quite why you would need to go beyond 10s or even 12s I do not know.

[widow_twanky]

Just looking into using perms at the moment. I know it's quite high but would just like to understand the rules before starting a proper design.

[geeza]

What controller are you planning to use? Because I bet it will blow up.

[widow_twanky]

What controller are you planning to use? Because I bet it will blow up.

Bet it wont as it's a simple bang bang controller with some chuffing big relays. Not for drive btw.

[Eventorizon]

The limit is 75V but there is a table in the rules that tells you the limit of each type of battery.
So you can only use a max of...

30 NiCd cells, 30 NiMH cells, 18 SLA cell's, 12 LiFePo4 cells or 12 Lipo cells.

So the limit may be 75 but even with a lipo at maximum voltage you will only reach 42V anyway.

[Max]

But you could use a large bank of capacitors to get your 75v from your 42v battery.
I think that would be allowed but you would have to check.

[widow_twanky]

Well that was the point of the question really. I saw the bit about voltage and the bit about cell count. Now I can keep to the cell count and connect them in series so each pack is within the limit and so is the voltage.

Just really wanted some clarification on that but decided to go pneumatic anyways.

[Bacon Wizard]

I was thinking either capacitor(s) or a "joule-thief" type of arrangement first, and then a cap to smooth things out.

[Max]

I was thinking either capacitor(s) or a "joule-thief" type of arrangement first, and then a cap to smooth things out.

What do you need the higher voltage for? If it is to run a drive motor or a motor that has to spin continuously then I imagine you will struggle. The capacitor idea I just for an axe or something which runs temporarily.

[Bacon Wizard]

It isn't strictly needed, but yes it's for a motor and if there's a way to get more power for the weight... I'll take it. Wouldn't you?

There's an obvious way: turn the supply into AC and then use a transformer. But that's horrible for weight. A joule-thief style arrangement might quite a bit lighter.

[Bacon Wizard]

I have 4 x 4700uF 63v caps if those are any use. They're not suitable for my voltage booster circuit, but someone else might find them handy... would like to hang on to 1 of them, but if you really need 4, would part with it.