Hello, long time lurker here.

I've got an old Honda MT5 moped with a blown engine lying around, and now im considering converting it to run of a battery.

I have some prior experience with motors and drives, but my experience with batteries and higher voltage DC systems is rather non-existant.

If anyone were to tell me that using a brushless motor operating on 48V is a very sensible option, i would agree. But i have a desire to use a common 230V 3ph induction motor, and an industrial VFD, because of reasons. A lot of VFD's will run happily on DC fed directly to its bus connections. However, this requires a lot more than 48V. I haven't checked any datasheets yet, but i can say for shure that the voltage required will be in excess of 300Vdc.

I dont know very much about Li-ion batteries yet, but it is my understanding that every single cell needs balancing in order to prevent over- and undercharging weak and strong cells. So i imagine a >300V, 100 cell li-ion battery managing unit as being a huge and complicated piece of hardware.

There is another option of course, i could use a 48V battery pack and a voltage converter. However, designing a converter that can handle 3-4kW both ways with minimal losses sounds like an even greater challenge, and i also need to consider weight and volume, as all of this needs to fit inside a small moped.

Now, im not asking anyone to design this project for me, thats my job. But i'd love some friendly brainstorming with you guys. In your opinion, which of the arcitectures mentionen above is more feasible? Is there anything i should be aware of, or have forgotten? Or do you perhaps have a better idea? i'd love to hear it.

Also, if anyone knows of any chips, datasheets or articles that could be of any help, be kind and point me to them.

Regards,
Torbjørn

 

You could try something in between.

90 VDC is a very common motor drive voltage for PM type motors.

96 volt battery (two 48 volt systems in series and easily placed in parallel for charging from common golf cart type chargers)

PWM circuit for power control. If it's good enough for golfers...

 

http://m.ebay.com/itm/RELIANCE-1-2-...3D302263365733&_trksid=p2056116.c100408.m2460

 

Thank you for your reply, and pardon my late response.

As i mentioned, im a sucker for the common asynchronous induction motor and i was hoping i could use one in this project. But you have given me an idea. By dividing my battery into several series connected batteries, each with its own simple bmc, i could possibly make the 300V battery setup without a terribly complicated central bmc. By charging in parallel as you suggested, there shouldn't be any need for a balancing system between each battery block, at least not while charging. They will all be charged to the exact same voltage. And if a cell fails, i could replace the battery without too much cost.

I've been reading an interesting article by Texas Instruments about their cell balancing techniques: http://www.ti.com/lit/an/slyt322/slyt322.pdf. The PowerPump technology decribed there sounds superb, but such high tech battery management might be overkill for my application.

But im starting to realise that i might need some form of dc-dc converter anyway: A LiFePo4 battery cell can swing from 2,5-3,6V depending on the charge state. If i have say 100 cells in series, that gives me a voltage swing of 365V - 250V = 115V. Theres no way that any VFD is designed to operate on such a wide voltage span.

Hmm-hmm, still more research to be done.

 

Hello, long time lurker here.

I've got an old Honda MT5 moped with a blown engine lying around, and now im considering converting it to run of a battery.

I have some prior experience with motors and drives, but my experience with batteries and higher voltage DC systems is rather non-existant.

If anyone were to tell me that using a brushless motor operating on 48V is a very sensible option, i would agree. But i have a desire to use a common 230V 3ph induction motor, and an industrial VFD, because of reasons. A lot of VFD's will run happily on DC fed directly to its bus connections. However, this requires a lot more than 48V. I haven't checked any datasheets yet, but i can say for shure that the voltage required will be in excess of 300Vdc.

I dont know very much about Li-ion batteries yet, but it is my understanding that every single cell needs balancing in order to prevent over- and undercharging weak and strong cells. So i imagine a >300V, 100 cell li-ion battery managing unit as being a huge and complicated piece of hardware.

There is another option of course, i could use a 48V battery pack and a voltage converter. However, designing a converter that can handle 3-4kW both ways with minimal losses sounds like an even greater challenge, and i also need to consider weight and volume, as all of this needs to fit inside a small moped.

Now, im not asking anyone to design this project for me, thats my job. But i'd love some friendly brainstorming with you guys. In your opinion, which of the arcitectures mentionen above is more feasible? Is there anything i should be aware of, or have forgotten? Or do you perhaps have a better idea? i'd love to hear it.

Also, if anyone knows of any chips, datasheets or articles that could be of any help, be kind and point me to them.

Regards,
Torbjørn

I'm going to think about my golf cart. I think it has about a 6HP 3 phase dc motor and runs on 125AH batteries at 48 volts.
Max speed about 32 mph and range of about 8 miles.
They make Lifepo4 batteries that are smaller and more efficient, but expensive.
I'm basically cheap, so I would try to use the "stuff" out of an EZ-GO RXV golf cart. I think the charger might also work. Just an idea.

 

Much appreciated. If your golf cart reaches 32 mph with a 6hp motor, then 3 or 4 kW should be more than enough.

 

Much appreciated. If your golf cart reaches 32 mph with a 6hp motor, then 3 or 4 kW should be more than enough.

It has a pretty neat system. Regen braking and no brakes. It's all done with the motor and electronics.

 

3ph induction motors don't do well for widely varying speeds and (comparatively) frequent starting and stopping under load. I understand the lure of doing a project like that though. I'm just not seeing it happening on "a moped".

NiMH batteries offer some advantages over Li, particularly regarding charging,,,,, but I might not be able to resist the challenge and experience either.....

Additionally, the cycle vehicle rids you (hopefully/mostly) of legal issues,,, BUT, you can do incredible stuff inside a tiny little old car and totally get away with it some places.

 

3ph induction motors don't do well for widely varying speeds and (comparatively) frequent starting and stopping under load. I understand the lure of doing a project like that though. I'm just not seeing it happening on "a moped".

Then there's the weight and size problem with an 'industrial' motor. Three phase motors are available in different forms for things like this, BLDC for instance.