modifying a 48v controller to run a 48v motor from a 36v battery

[eHomer]

I have a 1000w 48v brushless rear hub motor with the supplied 48v 1000w controller.

I also already have a 36v 12ah lithium-ion battery pack and charger which I`d like to use with it for now (while I save more money up !)

Reading the forum, I understand that the motor should work ok with 36volts, giving out a max power of about 750w, and would actually be under less stress than it`s specified 48v construction.

I do need to alter the low voltage protection circuit in the controller though, as it won`t run because it thinks the voltage from the 36v is too run down from the expected 48v.

I`ve opened the controller and it all seems nice an clear in there with accessible components. I just need to know which resistors to change !!

Is there anywhere where I might be able to download a circuit diagram ? It`s marked as " Brushless DC motor controller DM4825Li". I could photograph the board, and it is nice and clearly marked with abbreviations etc.

 

[Old_Dave]

It may not be as simple as that.... As there is also the 5v supply / 's to worry about.

May be a lot less agg to get a cheap 36v controller


Sent from my iPhone using Tapatalk

 

[Deleted member 4366]

Here's a doc on how to change it on an infineon controller. On a different controller, you've got to try and identify the the voltage divider that deals with it, and change the resistor in the same way.

http://www.ebikewheel.com/infineon.pdf
Also if you use Google to search for pages with "r12", "lvc" and "endless sphere" together, there's a few threads on how to do it.

Finally, there's this guy that has made a complete circuit diagram for a KU63 controller, so you should be able to figure out how it all works from there. You'll see it on pin 12 of the microprocessor, but on a different controller it'll be on a different pin. You'll have to follow the battery supply tracks and look for that same arrangement of three resistors and a capacitor.
KU63 motor controller

 

[eHomer]

That's excellent, thanks for the very rapid and informative reply.
I've compared the pictures with my own controller and I think it's going to need bit of tracing.
Here's the photos of my unit:

It sounds as though it should be an easy mod, just what I was hoping for.
I don't want to buy another controller when it could just be a question of changing one resistor !

 

[Deleted member 4366]

Those components above the end of the light grey wire look promising. It's possible that atransistor is switched to send a digital input to the processor.

 

[eHomer]

Thanks again. I'll read the documents you've indicated and check the circuits.
I'll reply on here again with photos when I get it sorted.

 

[NRG]

Good luck to you but I cant help feeling its would be easier to get a 36v programable controller and use that instead!

 

[eHomer]

I've had a good look at the controller now, and the chip is the same one as in Van Dalen's circuit diagram, an X8M06.
I'm trying to trace the under voltage detection pin 12, but I'm not certain that I've got the orientation of the chip right with the diagram. The chip has a circle corner marker at two opposite corners, and the diagram just has one at the top right.
If I'm guessing correctly, then it's on the top left corner, marked in my photo.
Do the miniature surface mount resistors there look like R50 in the diagram ?

Or am I looking in the wrong corner of the chip ?

Bearing in mind the 9.4k ohm in the diagram is for 36volts, what would my present 48volt cut off value be ?

I do very much appreciate the help I'm getting with this on here !

(It may be easier to buy a new 36v controller, but it would probably have to come from China and cost me about £30, whereas I may be able to modify this one for peanuts, and it would then be running at three quarters of the loading of a 36volt specified one...)

 

[NRG]

You can get a programmable Xiecheng one from e-crazyman (Keywin) off eBay. If he has them in stock they ship from a wherehouse near Heathrow. £20.

 

[Deleted member 4366]

I'd approach the problem a different way. You're looking for a pair of resistors with battery voltage on one end and ground on the other. You'd need to connect a battery to determine that. The pin on the microprocessor will either have an analogue input varying in the range between 0v and 5v or a digital input, where it'll be 5v above LVC and 0v below (or possibly vice versa). If you had two batteries =, one above and one below LVC, you could find the pin and work back from there.

However, the method you're using might work because it's similar to the KU63. The two resistors should add up to about 10k or maybe a bit more. The KU63 ones are marked as 1% so they have 4 digits on them and are in the ratio of 9 to 1, so yours should be in the ratio of about 12 to one. Assuming that yours is the same pin as the KU63, then we follow it out through the 2.2k (222) resistor to the 2k 1% one (2001), and then I can't see from there. Is there one with marking approx 2402 under that mauve capacitor? If so, you have it!

 

[jhruk]

I've had a good look at the controller now, and the chip is the same one as in Van Dalen's circuit diagram, an X8M06.
I'm trying to trace the under voltage detection pin 12, but I'm not certain that I've got the orientation of the chip right with the diagram. The chip has a circle corner marker at two opposite corners, and the diagram just has one at the top right.
If I'm guessing correctly, then it's on the top left corner, marked in my photo.

View attachment 4379View attachment 4380

If it helps here’s a picture of a ku63 showing pin 12. The orientation looks to be the same as yours so, as you say, pin 12 should be top LHS in your photo as well.

 

[Deleted member 4366]

Sorry, I'm not thinking. The other resistor would be between the 1 end of the 2001 resistor and battery voltage. The other end of that resistor goes to ground , which is that area to the right of it. Therefore, you need to trace where that via hole at the end of the 222 goes. It looks like it runs up the board closer to where the battery connection is.

Is it the one at the end of the grey wire?

 

[eHomer]

Thanks JHRUK, it does help, I now know I was following the right pin !

D8VEH, spot on ! I traced the board links underneath and it did take me over to the grey wire.

Here's another photo with the hidden lines shown and my estimate of the circuit from the suggestions.

Is it 7501 and 2402 ?

I'll measure their values. What should they be for a safe cutoff value below 36 volts ?

Maybe I'll put a switch on leads so that I can switch between 36v and 48v batteries.

 

[Deleted member 4366]

It should be the 2402, which is 24k. That gives a ratio of 12:1 like I expected, so that the processor will see between 4.0v and 3.15v. LVC will trip when it sees less than 3.15v. My calculation says a 17k4 (1742) will therefore trip the LVC at 30.5v.

So, replace the resistor with a 17k4 one or solder a 58k one in parallel with it, which will be a bit easier. Another possibility is to solder a 100k pot accross it so that you can set it to whatever you want.

Those big 1k resistors drop the voltage down for the regulator. It would be advisable to add another one in parallel to drop the total from 333 to 250 ohms. The KU63 has 180 ohms.

 

[eHomer]

Success !!

Many thanks to the prompt and accurate help from the forum.

You were spot on D8veh, I carefully unsoldered 2402 and replaced it with a metal film 18k ohm. (nearest stock sizes to 17.4 were 18 or 16). I also added the additional 2w 1k ohm to the group which did bring the combined res of those down to 250 ohm.

It needs very careful soldering, but I did have a 15 watt pencil iron and it was fairly easy with that, going very carefully. I bought another 24k metal film res in case I ever want to go back to 48 volts.

I've just tried it on the bike and it works perfectly with my fully charged 36v 12ah lithium ion battery. I can now give the bike a test and see how powerful it is at 36v 750w.

There's just one small thing, the simple three LED power meter on the twist grip always shows red, since I guess that's still expecting 48v. Is there any simple fix for that ? No worries if not, I have a 5 led level meter on the battery itself, though not readable whilst traveling.

Thanks again for the great help on the this, very much the "up side" of the Internet !!

 

[Deleted member 4366]

It would be a lot easier (and maybe cheaper) to get one of these, which is far more useful:
Waterproof Digital Voltmeter DC 15V To 120V Red Led Voltage Digital Panel Meter | eBay

 

[eHomer]

Yes, that looks a lot more useful than 3 lights !
Now ordered (2 of them, at that price !)
Thanks....

 

[PC2017]

eHomer are you still about and receiving messages??? I have read all this info and it makes little sense to me, that said I am too looking at a temp 36v battery to 48v motor however I do have a 36v controller, my question; if you remember that far back, how well did your motor fare speed wise at 500w I will be running at 15 amps??

 

[vfr400]

It's very simple. The motor will run at 3/4 of the mximum speed it did at 48v. The amount of power depends on the maximum current allowed by the controller, which is written on the label. The amps at 36v have 3/4 of the power than they did at 48v, so a 36v 20A controller gives 3/4 of the torque that you get with a 48v 20A one.

You need to tell us exactly which motor and the rating of your controller if you want an exact opinion.