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2V high current power supply for homopolar motor


stube40
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I need to design a power source capable of delivering high current (maybe 200 or 300A) at only 2V.

I thought I may be able to use TIs TPS40180EVM module - it has a lower current rating that I'm after, but you can stack them in a modular fashion.

However, I wondered if anyone had any better suggestions.

I'm more of a digital electronics guy, so designing from scratch is not a sensible move. Rather, something with a public domain reference design that I can just design into my own PCB would be ideal.

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Still why do you need 200A at 2V?

To create a large magnetic field?

How much power do you think you'll be able to generate?

You should only need 200A at 2V for a short period of time, once the generator is started, it should generate enough power to create its own magnetic filed, otherwise there's no point in it existing. If your generator isn't capable of generating the 400W required to power the magnets then it's pretty useless and well generate as much power as a heater.

All you should need is a large current pulse to get it started; a super capacitor can be used for this but I don't think it needs to be able to supply the full current and voltage, once the generator is primed, the filed current should increase as required.

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The desgin is a bit different from textbook homopolar turbines, so that may be confusing.

I have a working prototype of the motor here. Using a heavy duty Lab DC PSU, when we apply 2.0V to the motor it draws 100A at rotates at approx 2000rpm.

At 3.5V it draws 180A and rotates at around 3000rpm.

I need to hook up a torque transducer to the output to equate this to power (still trying to beg/borrow/steal one at the moment).

The main thing for me at the moment is to replace the Lab DC PSU with my own design.

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Hello, sorry if I antagonised you - that was not my intention. I'm here because I would like to be helped and upsetting people was certainly not on the agenda (and not a good way of going about getting help). Clearly I have misjudged the amount of information I would need to provide in order to get the ball rolling - for that, I appologise.

I have attached a basic diagram showing the layout of the system. I have also attached 2 scope traces that show voltage (yellow) and current (blue) measured across the brushes when the PSU is set to 2.0V and 3.0V.

I hope this is enough information now. To be honest, I'm not sure what other information I can provide right now. If there's something missing then please feel free to ask more questions and I'll do my best to answer.

Thanks,
Stuart.

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Sorry if I was a little harsh.


That looks like it will work but I do question why not use a standard DC or AC motor?

You could try using a ball bearing for the brush but I'm not sure how much it will minimise the friction losses.

I wouldn't expect to see anything through the 'scope, except for noise so the waveform appears to be correct.

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Homopolar motors offer some advantages in certain environments, particularly where low RPM, high torque is desirable. Also, they are so simple that they can be made to be extremely quiet (hence the reason they are often used in submarines).

Our experiment is to explore new and novel homopolar engines, particularly with respect to the materials used. In this instance, the actual power supply is secondary to the main aim. However, that's not to say that the PSU isn't important............

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I'm trying to drop the voltage of a 12V to approx 2V but allow many 100s of amps to be drawn, in order to provide power to an experimental DC motor.

I've considered many options, of which the TPS40180EVM module is my favourite so far.

However, I'm playing around with another option of turning the DC battery output into AC using a H-bridge to create a -12V / + 12V square wave then feeding this into a step-down transformer, then using rectification and filtering to create a 2V DC output (we can handle a bit of ripple in the motor). The advantage of this method is being able to handle the high currents with suitable choice of power transformer, rectification and filtering components.

I just wondered if anyone had any thoughts on this idea, or if anyone had any better ideas?

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Please keep to one thread for discussion of the same project. I've merged the threads into one and given it a sensible title.

Why not just use a 2V lead acid battery in the first place?

2V is the nominal voltage for a lead acid cell and can be bought from many suppliers. If you don't have a charger, you can connect six in series and charge them with a standard lead acid battery charger and connect them in parallel before use. You need to be careful that the cells are all charged to a similar voltage before paralleling them but that should be the case anyway if you get them from the same supplier and charge/discharge them at the same time.

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Thanks, and sorry for wasting your time with the double-thread.

I'm now starting to lean towards the 2V LA battery solution now as a real possibility. The reason I didn't jump straight into to this solution in the first place is two fold:

1) It leads to a pseudo fixed-voltage solution that is only adjustable in large steps (ie 2V). Whereas, it may be that I need to fine-tune the power source to 1.8V or 2.V in the future - clearly this solution can't be used in this fashion.

2) I have a array of good 12V batteries already in my possession

However, it's becoming clear that a suitable step down DC-DC that will give the low voltage, high current output from a 12V source is a non-trivial project, especially for someone like me that's non an expert in the area of switched mode PSUs.

I think this assumption is reinforced by the lack of suggestions from the forum regarding off-the-shelf solutions, such as the TPS40180EVM sync buck controller evaluation module. If high-current 12V-2V step down converters were readily available then I'm sure there would have been some alternative solutions suggested.

Thanks,
Stuart.

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