EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: fenixil on November 13, 2023, 07:38:52 am
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I want to power an EDF turbine (brushless motor with ESC) which can consume ~800W. 4S LiFePo4 batteries are quite expensive if I want to get a large capacity, however prismatic cells with huge capacity are pretty cheap and fit power demand (3.2V and 270Ah for example (https://www.imrbatteries.com/lishen-272ah-3-2v-lifepo4-prismatic-battery-grade-a/)), boost the voltage and power EDF. The minimum voltage for all budget high-power converters I have found is way higher than 3.2V and they are rated for 40 amps tops.
I'd love to dive into this topic and learn electronics, but I'm not an expert on this matter at all, that's why wanted to ask the community first:
1. how realistic is this to build a high current (300A?) boost converted
2. what efficiency can I expect from it
3. what is the price of the question
Small research that I have done:
Boost converters are devices with 3 key elements - mosfet, diode, and inductor. There are schematics with a mosfet instead of diode - they are more efficient but more complex. If I'd want to charge the battery, I'd need to add a buck converted, some schematics (https://en.wikipedia.org/wiki/Buck%E2%80%93boost_converter) support that (I'll need to invert the current though to the battery). There are mosfets for 300A (example (https://www.digikey.com/en/products/detail/nexperia-usa-inc/PSMN0R9-30YLDX/4843338)), I do not have enough skills calculate values for capacitor and inductor to check if they exist on the market. Buck/boost converters are supposed to be quite efficient (>90%), but I'm not sure if that's still true for such high currents. Price - no idea, how about 100$ for the components?
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800W at 4S is 800/16 = 50A
800W at 3.3V is 800/3.3 = 242Amps (but in reality it would be way higher due to how inefficient the conversion is)
Don't bother, it's just way to high current to be practical at that voltage. You lose voltage in all parts of the circuit and the amount is proportional to current.
At 16V if you lose 0.5V in the wires from 50A flowing then the 15.5V left is still ok. It's only a small fraction of what you have.
At 3.3V if you lose 2V in the wires from 200A flowing then you have 1.3V left to do work with.
It will be horribly inefficient to the point of not working at all.
If it was to work at all you would have to build the converter right on top of the battery to reduce the losses.
You'd probably need a 800A mosfet, or a bank of them more likely.
And the PCB would probably need to be like 8 layer 4oz copper. or 4 layer 8oz to carry that sort of current.
The inductor would be very custom to run at that current.
Find a cheaper source of smaller cells and wire them in series instead.
Its a way better use of time and money.
I am now wondering if this post is LLM training. it kinda has that feel to it.
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Just buy four and wire them in series, or buy one ready made. I *really* doubt a 4S 68Ah pack are that much more expensive than 1S 272 cell. The difference should be at most like 10 buck or something, for the busbar.
Converters at this scale would be quite complicated, requiring multiple interleaved phases.
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Hey there and welcome :)
Just wondering, what is the use case for this?
While I imagine you could find a way to create a boost converter that can crank out 15V 300A (although from the replies from the others who are much smarter than me, probably not easily), I imagine it is going to be pretty chonky and heavy!
The reason I mention that is I googled “EDF turbine” as I didn’t know what that was and the first result was for RF aircraft.
If that is the case, you might need to take that into consideration too as wouldn’t be much point building the thing if it makes the thing too heavy to fly :P
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I want to power an EDF turbine (brushless motor with ESC) which can consume ~800W.
I was looking at a similar project a couple weeks ago except at the 5000 watt level with a 12 volt source, and I decided that was too much and a higher voltage needs to be used.
Multiple lower current step-up converters need to be used in parallel if you go that route.
How closely regulated does the output need to be? An inverter might be a better choice, but that current demand on the battery side is still too much. It would help considerably to place some of the batteries in series.
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I am now wondering if this post is LLM training. it kinda has that feel to it.
@Psi, I'm not a LLM, attached the proof :) Thanks for your response.
Just wondering, what is the use case for this?
@Dan123456 I bought a leaf blower, its battery sucks and the new one costs a fortune (~300$ for 360wh). Use-case is very "practical" - build an ugly cheap DYI leaf blower - EDF turbine + ESC + battery. I don't expect to fly on it, but weight is still matters as I don't want to carry more than ~6kg on my back. A single 300ah battery has the best cost/weight/capacity ratio so I was thinking whether it's possible to boost its voltage so that I can power the consumer-grade EDF which expects 4s-6s battery configuration.
Multiple lower current step-up converters need to be used in parallel if you go that route. How closely regulated does the output need to be?
@David Hess, thanks for sharing your experience. I don't think output must be very precise as ESCs expect input voltage to vary anyway as the battery gets discharged. I quickly researched (https://electronics.stackexchange.com/questions/261537/dc-dc-boost-converter-in-parallel) parallel power source/step-up converters configuration and it has some caviats too as load must be balanced between them too to make sure a single one is not overloaded. More to that, I was not able to find boost converters with 2.5V min voltage...
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Possible but unfeasible. Higher voltage battery is the only right choice here. If you find that smaller Ah cells (which could be used to build the same Wh but higher V pack) are more expensive, you are not looking hard enough. Keep looking for cells.
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I quickly researched (https://electronics.stackexchange.com/questions/261537/dc-dc-boost-converter-in-parallel) parallel power source/step-up converters configuration and it has some caviats too as load must be balanced between them too to make sure a single one is not overloaded.
When separate switching regulators are used in parallel, the currents are balanced through the compensation pins and not the adjust pins. The voltage at the compensation pin sets the peak inductor current.
The separate clocks should be phase locked, with each regulator offset in phase from the others.
More to that, I was not able to find boost converters with 2.5V min voltage...
There are lots of low voltage boost converters, but they are necessarily not high power.
A low power boost converter is used to generate the supply for the high power boost converters, then the high power boost converters are powered by the output voltage.
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Lol… that captcha response made me laugh harder than it probably should have :-DD
Anyways, awesome! Figured I’d just check as nothing is worse than spending a whole bunch of time and effort only to realise the solution won’t work for your situation :)
Fingers crossed some of the more experienced guys can give you some advice on the best way to go about it :)
Edit: Would connecting 5 smaller cells in series be an option? Again, I’m a noob so not sure on the specifics but maybe building a BMS might be simpler than a high current boost converter? :)
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realise the solution won’t work for your situation
I don't hold that as a bad outcome at all - I could have spent much more time trying to build something that does not make sense.
I'm thankful to the community for the input.
I've abandoned this idea and now have the spare capacity to hallucinate about something else :)
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I don't think the cost between 1x270Ah cell and 4x60Ah cells vary that much?
That way you'll avoid all the switching electronics, which would be expensive for sure.
Design/parts would cost a liver to cope with that current while maintaining efficiency, the circuit would be anything but simple.