LifePo4 Vs Lipo 48v packs in electric racing kart setup
- Thread starter userix
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flippy said:
I have a battery meter with built in voltage display and when I floor it from a stand still. I see a voltage drop of roughly 3-4V. at a full charge, I can see the voltage drop from 54.5V to 50.1V, 50.1V being the lowest voltage during the drop.
Are headway cells better than lipo for my kart application? Better high current draw, etc?
e-beach
10 MW
flippy said:
I am heading towards 18000 miles on my Headway cells. They sag on the hills worse then when new, but still have 80% of original watt hours. So they don't suck in terms of longevity, although they don't have a high C rating in actual practice. If I were racing anything, Headway would not be my first choice though.
flippy said:
The Sevcon calibrator shows the current it's pulling into the controller (which is 300A when flooring accelerator), but as for the actual current going through, I don't have a meter to measure it. I'm not sure how I would be able to measure true current from the pack. Can I just use a standard ring clamp ammeter?
flippy
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motor phase current is not battery current. those are 2 different things.
and yes, get a ring meter that can do DC, or even better: a analog meter and a shunt, probably more accurate (it removes extremely short peaks that trip up digital meters) and more natural to read when driving.
and yes, get a ring meter that can do DC, or even better: a analog meter and a shunt, probably more accurate (it removes extremely short peaks that trip up digital meters) and more natural to read when driving.
flippy said:
https://www.amazon.com/AiLi-Voltmeter-Ammeter-Voltage-Motorhome/dp/B07FGFFHC6/ref=asc_df_B07FGFFHC6/?tag=&linkCode=df0&hvadid=366430786295&hvpos=1o3&hvnetw=g&hvrand=629383545751355415&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9031254&hvtargid=pla-569360505489&ref=&adgrpid=75985294733&th=1
Would this meter work for my setup to measure instantaneous current draw?
How about this ring type?
https://www.amazon.com/bayite-Digital-Current-Voltage-Transformer/dp/B01JIK8J3C
So my 48V PMDC motor should be spinning wheels from a stand still at a true 300A current?
flippy
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That ring meter should do fine.
And yes. 48v x 300a = 14.4kW of power or about 20 horsepowers.
No way you are remaining stationary or keep your grip with that amount of instant brute force.
I recon you also melt the winding pretty fast that way.
in theory you should be able to keep up with a proper sports car off the line or even get the drop on one the first 100ft
And yes. 48v x 300a = 14.4kW of power or about 20 horsepowers.
No way you are remaining stationary or keep your grip with that amount of instant brute force.
I recon you also melt the winding pretty fast that way.
in theory you should be able to keep up with a proper sports car off the line or even get the drop on one the first 100ft
999zip999
100 TW
Why not use leaf batteries automotive quality.
flippy said:
I have hooked up an analog and digital ammeter using a 500A 75mV shunt. And both the analog and digital gauges shows a rough max of 214A being pulled from the battery under the heaviest accelerative load. Does this mean my battery pack cannot truly output 300A?
flippy
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yes. you are 100A short.
so you only get 10kW (before losses) instead of the 15kW you have as your target.
you can compensate for this my increasing the voltage (just add more cells in series) so you keep the 200A but more volts = more power or get a better battery that can deliver a stable 500A or so. that is what you need if you want to get a easy 300 even when the battery drains.
it might also be because the motor simply cant absorb more amps.
so you only get 10kW (before losses) instead of the 15kW you have as your target.
you can compensate for this my increasing the voltage (just add more cells in series) so you keep the 200A but more volts = more power or get a better battery that can deliver a stable 500A or so. that is what you need if you want to get a easy 300 even when the battery drains.
it might also be because the motor simply cant absorb more amps.
flippy
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no.userix said:
it would be like complaining about the power consumption of a 2W brake light when you are consuming 10.000W at the same time.
its litteraly 0.02% losses of the total energy consumed that a shunt takes up in heat.
and the motor can prehaps take 300A but you still need a battery that can supply that power and a controller that can control that power.
fun fact: that controller you have probably has at least 4 shunts.
dustNbone
10 kW
A real time readout of the voltage going into the controller during a full power run would tell you alot. And maybe one right at the battery pack output to rule out your wiring. Just because the BMS can handle 300A doesn't mean the cells can, or the wiring connecting everything together.
And no, a properly sized shunt isn't high resistance, it's just a known resistance. It's probably less resistive than the piece of wire you're putting it into.
And no, a properly sized shunt isn't high resistance, it's just a known resistance. It's probably less resistive than the piece of wire you're putting it into.
flippy
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no, it means the battery can deliver 210A without destroying itself.userix said:
it probably -can- deliver more but you will reduce lifespan of the cells considerably and cause cell damage, overheating and so on.
the 3C rating is bascially the redline where the manufacturer stops giving warranty and expected/rated lifespan takes a nosedive.
max current to dependant on various things, mostly the resistance of the motor in this case.
because your voltage tanks under such loads you also reduce the amps that can flow.
increasing the voltage would help in overcoming the power limit you are hitting now.
if you cant increase the amps you need to increase to voltage if you want more power.
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