Controller voltage question

7 replies [Last post]
Joined: 11/19/2006
Points: 9

Have been have problems for a while with getting the full voltage to show up on my DrainBrain.

For the last month have been using a C'lyte 36-72v 40a controller with 100v(88.8v nominal) worth of batteries.Has been a pain to get the full voltage to show up all the time.
I will turn the main power(key) switch on and sometimes 29v/39v/40v will show up instead of a 100v.
Repeat on/off of the main power switch will eventually get it working.

It does the same when using 88v(77v nominal)
This controller only had a red button ON/OFF switch
I have checked voltage coming out of the connection going to the controller from the batteries and it is the proper voltage -the problem i think is the inrush of power to the controller trips something out.

In frustration i switched back to my 36-72v 20a dual controller which has a power key switch on it as well.
If i leave the controller switch powered ON when turning main power on -it will do the same -29v/39v/40v thing.
If i use 88v(77v nominal) -it will read that OK with this controller anytime.

If i turn the controller power switch to OFF -and then apply main power -i will get my proper 100v.

My question is- Is there an easy fix for this -maybe something that will leak the power in more slowly?

Cheers Dom

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Joined: 11/17/2006
Points: 34
I'm no expert

I'm not sure if true, but I heard that is normal. Have you simply left it on for a few minutes to see if it comes up to the proper voltage rating?

Do me a fav, use referral # 2724 If you order anything from e-ride (Greenwit). I want to see if they actually honour their referral program. Let me know as well please.

Fechter's picture
Joined: 11/17/2006
Points: 199
That's wierd

Yes, it sounds like the meter is tripping out. This sometimes happens if the power is cycled rapidly like if the switch contacts are bouncing or the inrush current is creating voltage spikes.
Does your system have a relay between the batteries and the meter?
Possibly a big capacitor across the power input to the meter would prevent rapid voltage changes.

Either way, if there is a main disconnect, it might be a good idea to figure out a pre-charging circuit. A precharging circuit is usually just a resistor that gets switched across the contacts to allow the main capacitors in the controller to charge up prior to closing the contacts. This prevents the huge current spike you would otherwise get when you connect a discharged cap to the batteries.

On my Vego, I have two power switches. The first one is the key switch, which puts a 1K 5w resistor across the relay contacts and enables the second switch. The second switch (on the handlebars) activates the relay and powers up the controller. I always turn on the key first, then use the handlebar switch to turn the scooter on and off.

Without precharging, I used to weld the relay contacts closed once in a while. This can ruin your day, not to mention it's rough on the relay contacts.

Joined: 11/19/2006
Points: 9
Hi Lesss - Tried leaving on

Hi Lesss -
Tried leaving on and power stays the same.I hadn't read of anyone having the same problem?
Hi Fechter
I have no relay between the batteries and meter.
I can take the meter out of the circuit and the same thing happens.
Surely other people must experience the same thing i get -not everyone runs at 48v haha.
When initially turning main power on there would be a current spike which fills the caps -but a quick turn OFF/ON with the main power should bring the power to the proper voltage don't you think?

When i turn main power off you can see the voltage drop over 5-6secs from 100v to 29v on the DrainBrain. (When i do get it going properly)What is that? -discharging caps?

The main power switch is a 20amp key switch which i have been using since i got my first ebike - almost 2 years. Thought that may be the problem and swapped it out with a new same type one,but it didn't change anything.

Did you make up the resistor for your Vego? Were you having the same type spike and not getting full power? Does the resistor get hot over time?
What Ohm/Watt resistor would you recommend for my situation?

PS have been running the 72v20a controller no worries for the last couple days(though i have never had any issues with this controller since day one)
Only have problems with the 72v40a controller.(since day one with higher voltages)

Cheers Dom

Fechter's picture
Joined: 11/17/2006
Points: 199

The slow voltage drop when you turn it off is the discharge of the main caps. My Vego didn't have a problem, but I just wanted to keep it that way. The main relay I'm using would take a beating without the precharge. Your main switch is apparently beefy enough to handle the current inrush. I used a 1K 5watt resistor. There's only a brief time when there's current in it, so it doesn't get hot. If I mess up and try to power the motor through the precharge resistor without the relay on, then it gets hot, but not destructively hot.

Just as a test, you could possibly rig up a 120v incandescent light bulb as a resistor.
If the controller has a logic power switch, turn it off first. Put the light bulb resistor across the terminals of the key switch and see if the meter will come up normally. Once the voltage comes up, then turn on the key switch.

Joined: 11/19/2006
Points: 35
This is why

Note for 72V users. On backlit DrainBrains shipped before Oct 26th 2006, it is possible for the backlighting LED to get damaged from an inrush current when it is plugged into a source above 80 Volts. Since fully charged 72V batteries are up to 85Volts, this can cause a failure. The fix is quite an easy one, simply replace the 120 ohm resistor R7 on the LCD circuitboard with one that is between 300 to 400 ohms.

This change is not necessary for 36 and 48V systems. If you have one of these units and plan to run with a 72V pack, please make sure sure to implement this change before plugging it in. I will mail the appropriate resistors to anyone who is comfortable doing the modification themselves, or I can do it at this end if you ship the meter back here.
Go here for more info:

Joined: 11/17/2006
Points: 23
thats fine for the led but...

I dont really see this being the fix. If the resistor is on the lcd board it shouldnt have anything do with the a/d in the microcontroller. This could be a fix for a blowing led but i dont understand how it would fix a false reading.
Im going to take a wild guess that the capacitors in your controller charging could be causing an inductive spike that the power supply in the drainbrain cant deal with. Could cause the microcontroller to latch up. I dont think its the current exactly thats doing it, i could be wrong. Does the drain brain update normally, as in when you move does it show amps and watts as it should or is it frozen like a sick pc running windows. In any case fechter(as usual) is right on in that you need a precharging circuit to get rid of the turn on spike.
Do the resistor fix also, just for the sake of the led in the backlight.

Joined: 11/19/2006
Points: 9
Thanks for replys Guys -have

Thanks for replys Guys -have been busy with a few projects.

Thanks Fechter -though i don't know how to implement your fix as of yet -haha!(me dummy) and it sounds like lots of wire!

Hi Tesco -the DB is not the problem -it is the voltage itself -and Buzzz did fix my new backlit DB before he sent it to me -works like a charm!

Hi Leeps -When i get the DB reading -just say 40v - i can use the throttle and a small amount of power will go to the motor -not enough to make the bike go- i will have to study up on how to make a precharging circuit.
I also had a few problems with the 72v40a controller (when i got the 100v in there) cutting power totally after switching motor modes -perhaps my batteries could be at fault as well -with the BMS's and all!

Have been running the 72v20a controller faultlessly at 100v(DB reading) for the last few weeks.
Maybe i'll save the 40a controller for when i get higher amp draw batteries. By then i should be an elec whiz hey!! LOL

Thanks Guys
Cheers Dom

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