102Views7Replies

What would be the best battery to provide 120v ac current at 10/20 amps for hours at a time? Answered

Im making an electric go kart

Discussions

Lets do a quick math:
20 Amps
120V AC
2 hours

120V AC @ 20 Amps = 2400 Watt
2400 Watt over 2h = 4800Wh
Lead-Acid batteries have 35-40 Wh/kg. This means around 128kg of batteries if we assume 100% efficient conversion DC//DC and from DC to AC (Which is for sure not the case).
For Lead-Acid batteries i would say, we are in the ballpark of 140-150kg Batteries per 2h

For LiIon:
100–265Wh/kg. Lets assume 180Wh/kg for reasonable prices...
This means around 27kg of LiIon batteries. (Be sure to mechanically protect those batteries! I can immagine the horrorscenario if you crash and rupture those packs! Definitely NOT NICE!)
I would say, ballpark-number there 30-33kg of LiPo batteries...

Both technologies are easy capable of 20 Amps continuous.
DC/DC-Conversion and DC/AC-Conversion is another topic entirely... A Battery discharges and lowers voltage. If you want constant Power, be sure to have the necessary voltage at the end of discharge... Buck-Converter for 20Amp are MUCH simpler than Boost or Buck-Boost for 20Amps.

Before we go further, are you sure you want to have 140kg of lead or 30kg LiPo on board??

I'm pretty new to this, can you find me a lithium ion battery that would work for this scenario?

What scenario? The one presented here or the new one you PMed me (48V-Motors)? I will reply to the new scenario in addition to the PM i already sent you.

OK. Lets go with the proposed (by you via PM) 48V and 100Ah.
As your packs in series will have to deliver about 50Amps for the 2400W, the C-Rating of the batteries is to be respected.
Lets have a look @ hobbyking.
Best bang for your buck will be something like https://hobbyking.com/en_us/turnigy-high-capacity-...
4s1p 20Ah with 12C. Weight: 2.1kg
20Ah @ 12C = 240 Amps. Works for your expected 50 Amps.
You will need to build a pack consisting of [4 in series of (5 in parallel)] to get the 100Ah (5 packs in series) and the 67.2V to 43.2V (4 of the previous 5-packs in Series) so a total of 20 batteries. 42kg batteries at a price of 20x118 Euro = 2363.4 Euro / 2628.93 US\$ without shipping and without Buck-Regulator and without DC/AC-Conversion. I would estimate about 3000US\$ for the electrical powertrain.

The engine im looking at already runs in dc to begin with. Why would you suggest against just buying 100 ah 12 v batteries and running 4 in series?

What about using only one battery and converting it into 120v from 12volts?

Good luck designing a DC/AC from 12V to 120V @ 20A out... Thats >200Amps inrush current to the coil...

Why not start the other way around?
Check what motor and gear system you need for the required torque and speed.
And then you might find a high voltage BLDC motor with controller is a suffient choice - if the gearbox is right.
And if in doubt one might even consider using one or two hub motors from an E-bike including the corresponding battery packs.