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#25 Reply
Posted by
Macbeth
on 29 Dec, 2014 04:10
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Blimey, I wouldn't have thought a polarity reversal during a battery charge could do that to a DP832. It's my second favourite PSU.
Thankfully I use my 6632B as a battery charger and it works a treat no matter what scummy cells you chuck at it. There is something to love about that old VFD beast.
Most lab PSUs - including the 6632B, do not support negative voltages across the output terminals. Bad Things can and will happen. HP recommends putting a diode in the circuit when charging batteries to prevent the crowbar circuit from blowing the internals out of the PSU.
Oh my old war-horse isn't as good as I thought. Well, now I know. Thank you.
I never would have tried charging reverse polarity batteries anyway - that seems pretty retarded - now I know I shouldn't do it ever ever ever.
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#26 Reply
Posted by
tautech
on 29 Dec, 2014 04:13
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2 things you can do in an attempt to protect your PSU
Diode in series, but allow for the V
f.
Dirty big Reverse bias diode across the terminals.
Maybe the sparks might alert you just in time.
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#27 Reply
Posted by
c4757p
on 29 Dec, 2014 04:52
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Seems to me it shouldn't be prohibitive for them to put a reverse diode and a bloody fuse on the outputs, and sense the voltage past the fuse...
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#28 Reply
Posted by
codeboy2k
on 29 Dec, 2014 05:17
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Seems to me it shouldn't be prohibitive for them to put a reverse diode and a bloody fuse on the outputs, and sense the voltage past the fuse...
Every lab PSU should be done like this, and I don't know why it's not. It does add parts and cost, but it's worth it on a lab PSU. You also have to sense before the fuse too, otherwise the feedback loop goes through the roof trying to bring the voltage up when the fuse is blown. Sensing before and after the fuse gives you a bonus: a fuse blown indicator too
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#29 Reply
Posted by
Skimask
on 29 Dec, 2014 05:38
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I never would have tried charging reverse polarity batteries anyway - that seems pretty retarded - now I know I shouldn't do it ever ever ever.
I didn't do it on purpose!
I put red on red, black on black....at the battery anyways.
For some dumbass reason, I had them reversed at the PSU jacks.
And I did get sparks, but they weren't that "big" and I figured the battery was just that discharged.
Quick look at the upper PCB shows D6 on channel 1 is a reverse diode. Have to break out the meter to verify it. Will handle that later.
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#30 Reply
Posted by
Nerull
on 29 Dec, 2014 22:43
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Seems to me it shouldn't be prohibitive for them to put a reverse diode and a bloody fuse on the outputs, and sense the voltage past the fuse...
Probably so, but lab PSUs are generally built to power DUTs, not things that will dump hundreds of amps back into them if the power fails. Battery charging is an instance where getting leads with an inline fuse might be a really good idea. The crowbar exists to protect the device being powered from a failure or voltage spike from the PSU, not the other way around.
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#31 Reply
Posted by
devanno
on 30 Dec, 2014 01:10
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@ivan - Good thought...about leaving channel 2&3 alone. And I ordered 20 of them. Not that I plan on smoking more channels or anything.
@Macbeth - I would've thought the same thing. Maybe there's a DP832 "reverse polarity input protection mod" in there somewhere.
And, yes, I should've walked the 50 feet over to the garage and grabbed my small battery charger to top off the battery, but, that was over there...and the DP832 was already right in front of me
If you have the spares, you won't need them. It's written in the rules somewhere. :-)
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#32 Reply
Posted by
Skimask
on 01 Jan, 2015 08:07
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Resistors showed up today.
Digikey part number is WSLK-.02CT-ND., .02ohm, 1%, 2Watt, 2816 package. (manufacturer part number is WSL2816R0200FEH )
Fit just right, work good, last long time, as long as I don't hook any more batteries up backwards.
I was going to do a quicky video on the fix. Decided against it. Just so dirt simple, if a person can't figure it out for themselves, probably shouldn't be messing around with it in the first place.
Ordered 20, got 19 left if anybody else decides to let some smoke out of their DP832.
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#33 Reply
Posted by
Skimask
on 02 Jan, 2015 07:27
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Well, so much for "last long time".
I thought it was working just fine yesterday. Ran some power thru a couple power resistors. Got volts, got current, got heat in the resistors after a bit of pumping a few watts thru them.
Then again...I was a bit tired. Maybe I was in channel 2 thinking I was in channel 1. Who knows...
Point is... Channel 1 is still dead. Shows "UR" on the display, varying voltage showing on channel 1 of ~.11-.15v, zero for current.
Thought I looked at everything well enough. Inspected all the traces I could see top and bottom, etc. Metered and inspected all the parts I could without a schematic, etc.
Guess I get to tear it down again and have another look.
Either that or just buy another "top" board for it and be done with it.
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#34 Reply
Posted by
Skimask
on 04 Jan, 2015 22:32
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Bit of an update...
Emailed Rigol looking for some info, parts, troubleshooting, etc.
Got the standard response of "proprietary design", blah blah blah. Ya no kidding.
I expected something else?
Anyways...and I feel like a bit of a dumbass. F3 (right next to the J12 input), a 5 amp fuse, is blown.
...DOH...
Thou shalt check voltages...any voltages...the presence or the lack of any voltages.
Guess what? Blown fuse, no volts. No shit right?
All I got for PCB mouse fuses is a handful of .3amp pico fuses laying around which were originally meant for rear projection TV convergence chip swaps.
Maybe one of those will work long enough for testing purposes. Maybe not.
We'll see in a few minutes...
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#35 Reply
Posted by
Skimask
on 04 Jan, 2015 22:55
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And not 15 minutes later...
A properly working DP832 with all 3 channels up and operating.
So, to summarize...
A- Wanted to top off a 12v Pb battery with my DP832 (maybe not a good idea in the first place?)
B- Hooked up the battery, red-to-red, black-to-black, but had the leads on the DP832 red-black, black-red (dumbass mistake #1, wasn't paying attention)
C- Smelled the smoked, unplugged everything. Test and found channel #1 inop, channel #2 and #3 working just fine.
D- Pulled it apart, found R52 (.02 ohm current sense resistor fried), and trace between D6 and positive output lead broken/lifted.
E- Replaced R52, fixed the broken trace with a chunk of 12ga solid copper wire laid over the broken trace, after removing some of the mask of course. No fix.
F- Profit???
G- Got pissed off at myself for not being able to fix it the first time, took it apart again, and measured the PCB mounted fuses. Found F3 next to J12 blown.
H- Replaced it with a .3amp PCB mounted fuse for testing. Worked good.
I- Found and swapped in a 5amp PCB mounted "PicoFuse". Found a 10ohm sand resistor, loaded it down as best I could, max'd out the voltage across the sand resistor. Resistor got good and hot (only a 10 Watt resistor sitting in a glass of previously cold water).
DP832 survived.
I'm happy. How 'bout you?
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#36 Reply
Posted by
tautech
on 05 Jan, 2015 03:47
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Yeah well we've all done some dumb shit at times, thanks for writing it all in your closing (we hope) post.
Just what we all strive for: a happy ending.
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#37 Reply
Posted by
devanno
on 05 Jan, 2015 04:16
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Glad it's working. Congrats and thanks for letting us know the resolution!
The "Profit
" line cracked me up... reminds me of an episode of South Park... heh
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#38 Reply
Posted by
macboy
on 05 Jan, 2015 14:26
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And not 15 minutes later...
A properly working DP832 with all 3 channels up and operating.
So, to summarize...
A- Wanted to top off a 12v Pb battery with my DP832 (maybe not a good idea in the first place?)
...
I use my lab supplies for charging SLA batteries all the time. They are perfect for this purpose: current-limited, fixed voltage. That's the definition of a proper lead battery charger.
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#39 Reply
Posted by
Skimask
on 05 Jan, 2015 19:03
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A- Wanted to top off a 12v Pb battery with my DP832 (maybe not a good idea in the first place?)
...
I use my lab supplies for charging SLA batteries all the time. They are perfect for this purpose: current-limited, fixed voltage. That's the definition of a proper lead battery charger.
[/quote]
True.
Maybe I should have stated I've got a few much cheaper options to top off a Pb battery sitting in the garage next door.
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#40 Reply
Posted by
nctnico
on 05 Jan, 2015 20:39
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Better put a diode in series when charging a battery. I got my HP 6002A cheap because someone didn't. The PSU overheated and because there was still more than 0V it decided to activate the crowbar. The owner believed it was beyond repair but the damage was just a few evaporated PCB traces.
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#41 Reply
Posted by
macboy
on 05 Jan, 2015 21:22
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I use my lab supplies for charging SLA batteries all the time. They are perfect for this purpose: current-limited, fixed voltage. That's the definition of a proper lead battery charger.
I'll revise my statement to say that the supplies I use do not have a crowbar, but do have a reverse protection diode.
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#42 Reply
Posted by
Skimask
on 06 Jan, 2015 23:25
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For future reference in case somebody else blows up channel 1 by doing the same thing I did...(mainly because you can't really order 1 of each of these parts at a half-decent price)
I've got 19 more replacement resistors for R52, and 9 replacement "pico fuses" for F3, sitting in my bins.
If anybody else needs one (or more), PM me and I'll slip them in an envelope and send them out for a few bucks.
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#43 Reply
Posted by
andrija
on 06 Jan, 2015 23:41
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Isn't "crowbar" just another (EE slang-ish) name for the diode in series, preventing reverse polarity? That's what I believed for the last 20 years (English isn't my first language though).
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#44 Reply
Posted by
rob77
on 07 Jan, 2015 00:36
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Isn't "crowbar" just another (EE slang-ish) name for the diode in series, preventing reverse polarity? That's what I believed for the last 20 years (English isn't my first language though).
no it's not. crowbar is a "trigger-able" dead-short across a supply rail. it's triggered in case of need to protect the load/supply. mainly used to avoid over-voltage - the idea behind is to rather blow a fuse than destroy the load with over voltage.
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#45 Reply
Posted by
SteveyG
on 18 Jan, 2015 20:22
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IMO positive should always be on the right. In the UK at least, TTI power supplies are pretty much the defacto standard equipment in most labs which have them this way, but actually every power supply I've used have the output this way around.
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#46 Reply
Posted by
Howardlong
on 28 Feb, 2015 23:55
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Well, I managed to fry my Ch 1 today when showing my nephew what happens when you put an electrolytic in the wrong way round.
PSU to 32V, 3A. 10V 100uF cap, wrong way around. Pop, magic smoke. But PSU starts saying it's overvoltage on Ch 1.
Then nothing, just a weak voltage slowly increasing, no error.
Took it apart just now, F5 was open circuit, replaced with 20mm 5A fuse soldered in. Back to the over voltage error - I measured it, about 50V - oops.
Took aim at the biggest transistor on that board, Q5, a CET CEP80N15. Pulled it off the board, all pins direct short to each other.
Had a look what else I had in stock as N Ch in TO220, all I could find was an IRF510, the Vgs looks alright, Vds a bit lower but the PSU won't be anywhere near 100V. On the negative side, the IRF510 is a mere wiper snapper at 5.6A continuous drain compared to the CEP80N15's 76A. But current isn't everything, it's power dissipation too, particularly in linear regulators like this. The IRF510 is still pretty bad at 43W compared to 300W for the CEP80N15.
Anyway, put it in and all seems hunky dory for now, until I get a proper replacement MOSFET that channel will be on emergency use only.
I am not sure if there is a hardware crowbar on this PSU. The programmed OVP and OCP still appear to function perfectly well, but I am not sure if that is a real crowbar or it just switches the transistor off. Either way, it is a bit of a nasty failure mode, 50V slapped right on the output.
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#47 Reply
Posted by
mcinque
on 01 Mar, 2015 09:56
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PSU to 32V, 3A. 10V 100uF cap, wrong way around. Pop, magic smoke. But PSU starts saying it's overvoltage on Ch 1.
I fear that some 832 could be defective: an intentionally reversed electrolytic on the output can (if I'm not wrong) be compared to a short, and I've tried that my 832 can handle that kind of issues at full power (as we all expect)...
What's your serial and calibration date?
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#48 Reply
Posted by
Howardlong
on 01 Mar, 2015 11:04
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DPC8C161250xxx
Digital version 00.01.11
Cal Time 2014-3-25
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Well, I managed to fry my Ch 1 today when showing my nephew what happens when you put an electrolytic in the wrong way round.
PSU to 32V, 3A. 10V 100uF cap, wrong way around. Pop, magic smoke. But PSU starts saying it's overvoltage on Ch 1.
Sad to hear. Was the cap fully discharged?
Cap may presented close to short circuit situation for a PSU. How can a short circuit bring down lab grade PSU? It is a complete fail
