This is my first forum post in my life....

[AppMan88]

Hello!

I have a VoilaMart 48v 1000w hub motor I have been using for about a year now. I read ALOT, dont know everything, still learning, and have alot more to learn. I have a question:

Is it possible to use 2 - 12v 100ah, or more, in series (24v×100ah=2400wh) and use(or build) a dc buck converter to convert 24v into 60v (2400/60=40ah)? The purpose of this is to cut down the amount of batteries bc I cant afford Li battery pack.

I already purchased a few 100v 470uf capacitors to replace 63v 470uf capacitors on the control board and it runs amazing. Any education on this matter would be awesome. Thanks.

 

[FlatSix911]

Welcome to EBR... I am sure someone knowledgeable can help you out.

 

[AppMan88]

Thank you. I sure hope so

 

[harryS]

First Question:
Here's a representative schematic for a KT-controller. I believe it's pretty typical. If you trace the battery power, you see it goes to the MOSFET's that drive the motor. In the top left, you can see the voltage converter section where the battery voltage is dropped down by two dc-dc converters to 14V and then 5V. You'll see the filter capacitors that you changed from 63V to 100V.

Hobbyists often change 36V controllers to run safely on 48V by changing to 63V capacitors, so you're correct in going to 100V.

Just one thing. Pull up the data sheet for the LM317T voltage regulator and you'll find the maximum input voltage is about 54V. There are other versions that can go to 60V, and if you have a 48V controller, it probably has the higher voltage regulator. Just saying you might blow out the controller in the future, but if you do, you know what probably blew up.

I'll try to include a PDF of the above schematic,

Second Question:

Yes, I've used a buck converter to boost a nominal 36V up to 60V, and than fed that into a 36/48V 22A KT controller. Zoom. Zoom. However, it was only a 20A output. I've not seen any that are more powerful. It also drew about 30A out of my battery and wasted about 30-40% of the battery power spinning electrons thru the transformer. Finally, my battery couldn't handle 30A, and blew a fuse.

The things are horrendously cheap. When I got mine, the coil was bent and one of the the blue trimpots was ripped off. The seller agreed to knock off 8 bucks, so final price was $18. AGain, I don't know if you can find one with much more output than 20A.

 

[indianajo]

Oh, I thought the OP was going to design a buck converter from scratch. ****ese garbage off ebay is a waste of time IMHO. The switcher supplies on ebay for 60 to 80 v power amps certainly don't have the reliability of a supply built into a Peavey or Crown amp or an Allen organ.
I had an Ishida 55 v 50 A switcher supply that developed a bad case of won't start on cold morning disease. Obviousy overaged rail e-caps. It was about 9" long x 6" wide x 2 1/2" thick about 6 times the size of the supply in your picture. But before I developed a need for it, the burglar carried off to the copper scrapper.
Other big problem with OP's plan is that Lead Acid batteries are not meant for deep cycling. Bicycle LiIon batteries are.

 

[AppMan88]

Thanks for the replies! I was thinking about designing and building a buck converter but I wanted to get opinions on that before I waisted time trying to build one.

I have 5 12v 20ah SLA batts in series on my bike. I been having them for about a year now. I've recently had a little trouble but I fixed that little problem. Ever since I exchanged the caps, havent had any issue and my batts stay charged longer.

I ride it to and from work, approx 7 miles a day. With charging every other day.

 

[AppMan88]

I have been researching schematics on my control but never could get close to it. Idk where to look.
My idea was to run from the batteries to the buck converter (with a display and fine tune pots), then to the control. I also thought about placing a 100v 2200uf cap between the buck and the controller to somewhat relieve the batteries from constant drain but I wasn't sure if that was going to work like I think it would work.

 

[AppMan88]

Oh, I thought the OP was going to design a buck converter from scratch. ****ese garbage off ebay is a waste of time IMHO. The switcher supplies on ebay for 60 to 80 v power amps certainly don't have the reliability of a supply built into a Peavey or Crown amp or an Allen organ.
I had an Ishida 55 v 50 A switcher supply that developed a bad case of won't start on cold morning disease. Obviousy overaged rail e-caps. It was about 9" long x 6" wide x 2 1/2" thick about 6 times the size of the supply in your picture. But before I developed a need for it, the burglar carried off to the copper scrapper.
Other big problem with OP's plan is that Lead Acid batteries are not meant for deep cycling. Bicycle LiIon batteries are.

My motor is 48v 1000w. I'd figure 1000/40=20.83 so I would only need 21 amps...correct?

 

[harryS]

Your motor may say 1000 watts, but it will draw whatever max amps your controller can supply, and I don't believe that changes with voltage. What's the controller label say?

Call it a 20A controller. At 60V, you need 1200W from the converter. If you have 24V worth of battery, you need 50A of input current. So you won't be minimizing the SLA count as much as you hoped. You'll have to run them in parallel. There's also the effciency argument. These are about 60% efficient. Your batteries will drain even faster.

I did mine for a lark. Twenty bucks and I can crank up my 36V bike to as much as I dare and see what happens.

There was a guy on Endless Sphere running his 48V bike successfully on a half dozen $25 36V4AH hoverboard packs. That's where I got the idea, and I also have some of those same packs.

Using the Wangdd22 1500W 30A DC Boost Converter on an ebike

Using the Wangdd22 1500W 30A DC Boost Converter on an ebike. Background: Why bother? Short answer - economy, versatility and fun to try. Longer answer: This is my first e-bike and I'm trying to keep costs down. I bought a used donor mountain bike ($180) and a $225 rear wheel kit (48V...

endless-sphere.com

 

[Admin]

@harryS, you're awesome! Thanks for the technical replies here... I learned a lot too