back to 115V 20A modified controller

[Antonio Zanardo]

After repairing the stock 48V 20A controller, modified to stand 115V, I bench tested it at 140V before placing it on the bike.

I ascertained the low voltages were a regular 5V for throttle and 14.2 for motor hall sensors. However, the only big resistor placed on the board was very hot after a couple of hour test. I was even unable to determine its resistance value, as the color bands were almost baked.

I suppose this resistor has something to do with the low voltage rail, as NO motor was connected to the controller during the bench test.

First question: what would be a suitable resistance value in order to prevent overheating of this component at a high 115V?

With the 115V supply I road tested the bike for several kilometers, at 100% throttle. The bike topped 58-61 kph.

A Watt's Up meter was connected to half battery voltage as it cannot stand the full 115 voltage.

Second question. I suppose the amps reading should be the actual current draw, while the watts and volts readings are half the real value. Is that right?

At full 100% throttle, the meter shows 20,1 amps draw, which is the top amps the controller can supply. However the power should be high, as a nominal 115V*20.1A= 2311 watts. I didn't take into account the voltage sag, though.

So far everything is working right. I hope it will continue that way.

Thank you in advance for your answers.

Antonio Zanardo

 

[xyster]

A Watt's Up meter was connected to half battery voltage as it cannot stand the full 115 voltage.

Question Second question. I suppose the amps reading should be the actual current draw, while the watts and volts readings are half the real value. Is that right?

Correct. Like the rate at which water passes through a hose, current at any point in a particular circuit will be the same because, like water through a kinked hose, the overall flow is controlled by the rate at which current can pass through the most resistive part of the circuit, the rest of the electrons backing up behind that point.

Don't know about the resistor value.

 

[The7]

"I ascertained the low voltages were a regular 5V for throttle and 14.2 for motor hall sensors. However, the only big resistor placed on the board was very hot after a couple of hour test. I was even unable to determine its resistance value, as the color bands were almost baked."

Do you mean this R?

 

[The7]

Some maths for this 3k R.

Assume this 3k res drops 48V to 14V .
Currnet = (48-14)/3k = 11mA
Power = (11m*11m) 3k = 363 mW
OK for an 1W res.


Now dropping from 140V to 14V
Current = (140-14)/3k = 42mA
Power = 5.3 W
Will burn 1W res in a short time.

 

[Antonio Zanardo]

Some maths for this 3k R.

Assume this 3k res drops 48V to 14V .
Currnet = (48-14)/3k = 11mA
Power = (11m*11m) 3k = 363 mW
OK for an 1W res.


Now dropping from 140V to 14V
Current = (140-14)/3k = 42mA
Power = 5.3 W
Will burn 1W res in a short time.

Yes, the resistor is the one shown in your picture.

By replacing that resistor with a 8.2K, and considering that the actual work voltage is 115V, the new values should be:

Voltage drop 115V to 14V
Current = (115-14)/8.2k = 12.3ma
Power = (12.3*12.3)*8.2=1.24W

A 8.2K 2W resistor should be ok.

Is that right?

Thank you.

Antonio Zanardo

P.S. please forgive me if I ask dumb questions. Actually I am not at all familiar with electronic maths.

 

[Antonio Zanardo]

To The7

Your picture shows a 20A controller missing two mosfets at the left hand of the board. My understanding is that you had some problems with them, therefore you are going to replace them.

The odd thing is that my same type controller blew TWICE exactly the two SAME mosfets as yours. Have you an idea why those two mosfets should blow so frequently, while the others one do not?

Antonio Zanardo

 

[The7]

Yes, the resistor is the one shown in your picture.

By replacing that resistor with a 8.2K, and considering that the actual work voltage is 115V, the new values should be:

Voltage drop 115V to 14V
Current = (115-14)/8.2k = 12.3ma
Power = (12.3*12.3)*8.2=1.24W

A 8.2K 2W resistor should be ok.

Is that right?

Thank you.

Yes.

It is better if y could also change the surface mount R3 (33k) to an ordinary R 33k 1/4W.

 

[The7]

To The7

Your picture shows a 20A controller missing two mosfets at the left hand of the board. My understanding is that you had some problems with them, therefore you are going to replace them.

The odd thing is that my same type controller blew TWICE exactly the two SAME mosfets as yours. Have you an idea why those two mosfets should blow so frequently, while the others one do not?

Antonio Zanardo

It is free to me when I bought an good used one.

The two FETs are on the yellow branch (phase).
I do not know the exact algorithm of the switching sequence in starting.

Do it always start switching ON with the same branch or randomly?
If it always start with the same branch, the FETs of that branch will mostly blow first.
If it starts randomly, any branch FETs have equal chance.

Wonder if any other had such experience of blowing the yellow branch FETs?

 

[The7]

Old version of mine has an faulty FET driver on the yellow branch.

The yellow branch AGAIN!!