[Buk]

I'd like to design and build a DC-DC converter for my e-bike to nominally take 36V in and uprate it to 48V. I know just enough about electronics to be dangerous and will need a heap of research/hand-holding.

Is this the right place for a beginner to find pointers and help for such a project? If not, I'd rather bow out now than bug people.

I'm attracted to the "split-pi" circuit because of its claimed efficiency: >98%. I'm aware its a patented circuit but as this is a one-off for my own use, I don't believe that is a problem.

I'll stop there and expand if there are any positive responses.

Cheers, Buk

 

[Alec_t]

Welcome to EP!
I can't see any advantage in using a split-pi circuit, which is essentially a buck-boost converter. Your required output voltage is always above the input voltage, so a boost converter seems to be all you need. Converter design (of whatever flavour) is far from trivial.
Will your batteries be able to cope with the ~78% increase in power demand that going from 36V to 48V implies?

 

[BobK]

A 40A converter is not trivial. Adding another 12V battery would likely be less expensive, more efficient, and increase, rather than decrease your capacity.

Bob

 

[AnalogKid]

Don't confuse claimed efficiency for an extremely narrowly defined application with a generalized characteristic of the topology. You will *not* get that kind of efficiency in you application.

Separate from that, the circuit is overly complex for the problem you have described. It's only advantage is the way it handles regenerative braking. If you aren't doing that (and the power control for that is very complex), then a synchronous boost converter is your best option. As above, a 40 A output will require a 60 A input for your nominal spec, and 120 A worst case.

ak

 

[Buk]

Separate from that, the circuit is overly complex for the problem you have described. It's only advantage is the way it handles regenerative braking.

You hit the nail on the head. The bi-directionality is the second thing that makes the split-pi configuration attractive. My controller already handles regen; so being able to feed its output back to the batteries is another goal.

The 40A requirement is peak, momentary and unusual. 25A continuous is more than enough for all but the most unusual of circumstances.

The battery pack is good for it.

 

[Buk]

Welcome to EP!
I can't see any advantage in using a split-pi circuit, which is essentially a buck-boost converter. Your required output voltage is always above the input voltage, so a boost converter seems to be all you need. Converter design (of whatever flavour) is far from trivial.
Will your batteries be able to cope with the ~78% increase in power demand that going from 36V to 48V implies?

It's bi-directionality allows for regen.

 

[Buk]

A 40A converter is not trivial.

I didn't expect it would be. I know there will be a steep learning curve.

Should I take this and the general lack of enthusiasm to mean that I'll need to look elsewhere for help in getting started?

 

[HarryA]

Consider changing the sprocket at the rear wheel. On my electric scooter I replaced the rear sprocket from 60 teeth to 80 teeth to reduce the speed and get more power. If you want more speed use a smaller sprocket. I got my Razor scooter sprocket from England via Ebay.