DP832 blown channel 1

[shaynet]

Hi,

I've been charging tool batteries on my Rigol DP832 (on channel 1). when I changed from one battery to another, I disabled the output of the channel.
when making the connection to a new battery there were sparks then the display showed some error and the magic smoke came out.
after this channel 1 shows UR.
now, if I enable the output the display shoes the output voltage creeping up very very slowly.

I pulled the channel 1 board and I have a few observations:
1. no shit stains anywhere
2. F3 fuse is blown
3. when measuring the Main mosfet in circuit - it's not showing a short
4. D6 diode is missing

while I'm looking for something to replace F3 fuse a few questions:
1. should I remove the FET to test it or is it enough that it's not showing a short in circuit?
2. should I add D6? and what is the part number for it?
3. anything else to check?
4. what did I do wrong? is it not ok to connect a battery to the output while it's disabled?


thanks!

[Bud]

You should have used a diode between the PS and the battery to block reverse current from flowing from the battery into the PS.

[J-R]

I didn't find a specific explanation of the crowbar circuit on this power supply, but it sounds like that is what happened.  Hopefully you got lucky and you can replace the fuse and be back in business.

It is tempting to use bench supplies to charge batteries, but this and a few other reasons make it questionable IMHO compared to using a charger designed for the battery in question.  The crowbar circuit, of course, but beyond that most battery/charger setups have balancing/health detection for individual cells in the pack, temperature monitoring/compensation and most likely a multi-stage charging plan with various voltage/current setpoints.

Sure, not every setup will have all of that, but almost all Li-Ion tool battery/charger setups have at least the detection for an individual cell that has fallen below a specific voltage, at which point it will refuse to charge the pack for safety reasons, as well as a high temperature cut-off (from charging or from heavy tool use).

[Muttley Snickers]

Hi,
I've been charging tool batteries on my Rigol DP832 (on channel 1). when I changed from one battery to another, I disabled the output of the channel. When making the connection to a new battery there were sparks then the display showed some error and the magic smoke came out. After this channel 1 shows UR. Now, if I enable the output the display shoes the output voltage creeping up very very slowly.

I pulled the channel 1 board and I have a few observations:
1. no shit stains anywhere
2. F3 fuse is blown
3. when measuring the Main mosfet in circuit - it's not showing a short
4. D6 diode is missing

While I'm looking for something to replace F3 fuse a few questions:
1. should I remove the FET to test it or is it enough that it's not showing a short in circuit?
2. should I add D6? and what is the part number for it?
3. anything else to check?
4. what did I do wrong? is it not ok to connect a battery to the output while it's disabled?

Here is a thread linked below which might be of interest where a fellow member also damaged channel 1, he has traced out part of the circuit and posted the schematics. Also, it might be best if you were to move this thread to the repair section.

https://www.eevblog.com/forum/repair/rigol-dp832-channel-1-analog-board-schematic-fragments/

[RoGeorge]

4. what did I do wrong? is it not ok to connect a battery to the output while it's disabled?

You missed this:  https://www.batronix.com/pdf/Rigol/DP8_DP1_ActiveLoads.pdf

You must put a diode in series with the battery to be charged, or else risk to damage the power supply, or even worst, risk to start a fire.  Things can go wrong from reasons outside of your control, for example a mains power outage, an internal short circuit inside the power supply, and so on.

Batteries can supply huge currents, and in case of a short-circuit they can heat the wires red-hot and start a fire.
Always add a series diode when charging batteries with a power supply.

[shaynet]

update for future reference:

I found the missing D6 diode - it was rolling around inside the power supply perfectly intact . my guess it was hanging by a thread and fell off during shipping. I'm lucky it didn't short anything out all these years.

• I soldered D6 back in place.
• replaced F3 with a 5A fast blow fuse.
• turned on the power supply and the fuse blew.
• couldn't find anything wrong.
• replaced F3 with a 7A fast blow fuse.
• everything works!!!!!

I feel like I dodged a bullet

[MathWizard]

I was testing a mosfet/heatsink one time on my Siglent PSU, and sometimes, it would get very hard to turn the mosfet back off right away, by lowering the gate voltage, and I mean on the order of seconds, and me thinking I'm going crazy. My understanding is gate capacitance is very small, so it's not just the gate was stuck high.

So in general would something like ever happen inside the PSU, when going from some big steady load for ages, to another 1, I don't mean like an inductor, I just mean transistors getting stuck on ?  I should try it again, with it on a scope.