Another issue with the Rigol DP832 power supply: sense wires carrying 3 amps!

[Rufus]

if you source current from Ch3+ and sink it into Ch2-, the current flows through the voltage sense wires and induces a drop (and therefore error in voltage readout/regulation)

The real fail (ignoring lack of isolation between the two supplies) is having two terminals for the common connection. It doesn't provide any useful function, just tends to confuse the user.

Having significant resistance between the two terminals is a secondary failure.

[rs20]

You wouldnt think remote sense would be needed for a 3A supply. 1 + 1 =2 Feet of AWG18 would be about 40mV. Remote sense can really hamper dynamic response and is more likely to cause stability issues.

Nono, this power supply doesn't have remote sense wires. Sorry, I should have been clearer. I'm referring to the sense wires internal to the supply -- they measure the voltage right at the terminals, so the voltage drop on the leads from PCB to terminals aren't a problem.

In any case, 40mV exceeds the 10mV accuracy spec for the supply, so the sense wires are totally legit.

[rs20]

The accuracy spec is probably for at the terminals. You can’t really cant really spec accuracy any other way then where it is sensed.

Yep, it's good that the spec is for the voltage at the terminals; it's very bad that the reading can be way out of spec (the topic of this thread)!

[AndersAnd]

Recommended Connections: DP832 CH2 and CH3 COM Terminals

http://beyondmeasure.rigoltech.com/acton/attachment/1579/f-034c/1/-/-/-/-/DP832%20Proper%20Connections.pdf

[rs20]

Yeah, I saw that... I think it's pretty poor, really. "Hey, our power supply has a massive flaw where the voltage sense wires are carrying 3 amps if the user uses a common ground return lead, let's just declare that sort of connection to be 'incorrect'. Problem solved!"

[rs20]

I threatened it in the original video, and it's only been several months, so I figured it was time! I soldered a bit of 3mm (!) copper wire between the two negative terminals, and the problem is fixed, no surprises. Post-fix, voltage sag on channel 2 is about a millivolt or so (noise floor of my cheapo DMM, compare to 57mV dip pre-fix) when injecting 3A up where it doesn't expect it. A video demonstrating the (more-or-less ideal) behaviour of the supply after the fix is below.  No, there's no video of the fix itself, sorry! I don't have Dave's talk-and-fix-and-operate-camera-at-same-time skillz...

[eurofox]

I threatened it in the original video, and it's only been several months, so I figured it was time! I soldered a bit of 3mm (!) copper wire between the two negative terminals, and the problem is fixed, no surprises. Post-fix, voltage sag on channel 2 is about a millivolt or so (noise floor of my cheapo DMM, compare to 57mV dip pre-fix) when injecting 3A up where it doesn't expect it. A video demonstrating the (more-or-less ideal) behaviour of the supply after the fix is below.  No, there's no video of the fix itself, sorry! I don't have Dave's talk-and-fix-and-operate-camera-at-same-time skillz...

Hi,

I intend to buy such a power supply, maybe someone who bought it recently could confirm or not that it is fixed in the mean time?

eurofox

[sacherjj]

I intend to buy such a power supply, maybe someone who bought it recently could confirm or not that it is fixed in the mean time?

I will be checking mine out when it arrives.  But the ship notice for my DSO4054 also includes a ship date of 2014-05-02 for the DP832.        Looks like the DM3068 is also 2014-05-02.   

Maybe they are reworking the DP832 again.  Or TEquipment just has stock issues.

[tequipment]

We.. tequipment.. are backordered.. we cant keep up right now with depand.  I hope to get ahead of it soon.

Thanks
Evan

[grego]

No worries Evan. You guys always treat us right.

[Sparky]

I intend to buy such a power supply, maybe someone who bought it recently could confirm or not that it is fixed in the mean time?

Hi eurofox, there were some similar questions about the DP832 status, which I replied to here.

Also, you may wish to follow my thread on DP832 firmware bugs and hardware issues here.  I will try to keep the thread up-to-date.

As for the specific issue you mention (design fault related to current sense between GND terminals of channels 2 and 3), we don't know whether Rigol will correct it in a future hardware revision, but so far there are no reports of them fixing this issue.  If I have to guess, I would say it is not likely they will provide a fix --- they had a chance to do it when the LM317 heatsink problem was addressed, and also Rigol has replied directly about this issue in "DP832 Recommended Connections.pdf" (see my thread linked above, or post #30 above by AndersAnd) in which they suggest installing a heavy duty GND wire yourself.

Hope that helps!

[eurofox]

I intend to buy such a power supply, maybe someone who bought it recently could confirm or not that it is fixed in the mean time?

Hi eurofox, there were some similar questions about the DP832 status, which I replied to here.

Also, you may wish to follow my thread on DP832 firmware bugs and hardware issues here.  I will try to keep the thread up-to-date.

As for the specific issue you mention (design fault related to current sense between GND terminals of channels 2 and 3), we don't know whether Rigol will correct it in a future hardware revision, but so far there are no reports of them fixing this issue.  If I have to guess, I would say it is not likely they will provide a fix --- they had a chance to do it when the LM317 heatsink problem was addressed, and also Rigol has replied directly about this issue in "DP832 Recommended Connections.pdf" (see my thread linked above, or post #30 above by AndersAnd) in which they suggest installing a heavy duty GND wire yourself.

Hope that helps!

Thanks Sparky

[Macbeth]

I intend to buy such a power supply, maybe someone who bought it recently could confirm or not that it is fixed in the mean time?

I will be checking mine out when it arrives.  But the ship notice for my DSO4054 also includes a ship date of 2014-05-02 for the DP832.        Looks like the DM3068 is also 2014-05-02.   

Maybe they are reworking the DP832 again.  Or TEquipment just has stock issues.

Snap!

I've got a DP832 and a DM3068E on order with TEquipment with an estimated shipping date of 2014-05-06! I placed my order on 2014-02-28 and only a couple of days before could swear both were in stock.

Oh well, I've checked other Rigol suppliers both closer to home and China, but none of them have any real stock either.

My problem is I paid paypal to make things easier for us. But it just means my cash is in TEquipments pockets until despatch, whereas if I paid with credit card then the charge would be authorised but not taken until despatch.

Having worked in telephone sales/accounting for a small company, I can tell you there was never a deliberate policy, but people who only paid deposits or cash on delivery got the goods quicker than anyone who paid upfront and left us to it without nagging us. Anyone who paid bank transfer or charge card in full - welcome to the back of the queue (paypal didn't exist then).

So, I feel this will put me at the back of the queue. Can I reverse my paypal and then give credit card details seeing as this cash is tied up for so long? Problem is paypal rips people off on everything and reverse transactions incur inflated forex fees so not so good.

I appreciate the delay is none of TEquipments fault but would like to be reassured that first come first served is somewhat the policy?

The only good thing I can think of is Rigol are improving their products, hence the manufacturing delay? (Clutching at straws!)

[echen1024]

Wait, Macbeth, so you ordered in the future?

[Sparky]

I appreciate the delay is none of TEquipments fault but would like to be reassured that first come first served is somewhat the policy?

If you read above, Evan from TEquipment.NET has said stock is simply backordered.  TEquipment.NET is a huge distributor with a solid reputation.  I've never had any problem with them, and cannot imagine them pulling any dodgy business like you're thinking --- the queue is FIFO.  So yes, you're at the back of the queue, behind everyone who ordered before you.

[tequipment]

we have a few hundred coming in on this shipment with about 100 left so we are good.. ( when they finally get there )
Thanks again for the business.

I just got 5 kids to bed.  After 11 hours of work I'm dead tired. 
Cheers and many thanks for the business!
Evan Cirelli
TEquipment.NET

[Macbeth]

we have a few hundred coming in on this shipment with about 100 left so we are good.. ( when they finally get there )
Thanks again for the business.

I just got 5 kids to bed.  After 11 hours of work I'm dead tired. 
Cheers and many thanks for the business!
Evan Cirelli
TEquipment.NET

      

Thanks Evan and Patrick for sorting out a switch from paypal to credit card for my order. I really look forward to it! 

[tequipment]

The credit should have been done today..

Thanks
Evan

[Rigby]

(design fault related to current sense between GND terminals of channels 2 and 3), we don't know whether Rigol will correct it in a future hardware revision, but so far there are no reports of them fixing this issue.  If I have to guess, I would say it is not likely they will provide a fix --- they had a chance to do it when the LM317 heatsink problem was addressed, and also Rigol has replied directly about this issue in "DP832 Recommended Connections.pdf" (see my thread linked above, or post #30 above by AndersAnd) in which they suggest installing a heavy duty GND wire yourself.

It's a design flaw; it won't be corrected until a new model is released, if then.  A fix to the DP832 would require more work than they'd be willing to put into a model that costs as little as the DP832, given that there is a workaround.

More costly models would get the attention that their cost demands.  This supply isn't worth the effort, likely. 

Just be aware of the issue this supply has and you've armed yourself with everything you need to use it effectively.

[neslekkim]

So I found this thread while I'm reading up on this psu, so I guess the situation still is the same on this?
Not sure in what situation I would combine ch2 and ch3, but I would use an combination of ch1 and ch2 to provide -15/+15 power, but I guess I would use ch3 for powering the 5v part of the same circuit, would I be in this situation then?

on the DP831, did they change this there?, the ch1 is the low-voltage channel, and ch2+ch3 is the ones with higher voltage, and common ground it seems from the pictures.

Maybe just continue looking...

[rs20]

So I found this thread while I'm reading up on this psu, so I guess the situation still is the same on this?
Not sure in what situation I would combine ch2 and ch3, but I would use an combination of ch1 and ch2 to provide -15/+15 power, but I guess I would use ch3 for powering the 5v part of the same circuit, would I be in this situation then?

Yes, that's exactly the problem use-case I suggested in my video, +/- 12V with a 5V logic rail on the same ground.

on the DP831, did they change this there?, the ch1 is the low-voltage channel, and ch2+ch3 is the ones with higher voltage, and common ground it seems from the pictures.

Don't know; the DP832 says it has common grounds on CH2 and CH3, and it does: but only via the voltage sense lines.  The fact that the DP831 says it has commoned grounds doesn't imply much.

Maybe just continue looking...

You're not going to match the features and accuracy of the DP832 for the cost. The issue is A) limited to a 57mV error which is insignificant in most cases, B) easy to avoid by returning the current to the ground from which most of the current is coming, and C) easy to permanently fix as well as I outlined in the following video. So overall, I'd still choose the DP832 any day, unless someone can suggest a concrete alternative (ironically, there's a lot of "my old analog power supply was fine" sentiment, where we're talking about a 0.057V error!!!)

[neslekkim]

Thanks!, that is good to know, 57mV is of no concern , I was more worried about the 3Amps on the sense wires, but doing it "properly" according to the guides that Rigol gave out earlier it should be ok. Will check out your video also.

I checked with the Rigol pusher in Norway, and find that the dp832 is very affordable.. even for this country.

[PioB]

So if I understand correctly, if one wants to drive dual rail Op Amps and some digital logic (with split analog/digital grounds), one would be better off with something like the GW Instek GPS-3303S or an QL564T by Aim-TTi, without common grounds, but then one would be looking at two to three times the cost of the rigol?
 (Power supplies taken arbitrarily from a Swiss distributor website, I checked for 3 outputs and > 195 W and the price not in the stratospheric range)

[rs20]

So if I understand correctly, if one wants to drive dual rail Op Amps and some digital logic (with split analog/digital grounds), one would be better off with something like the GW Instek GPS-3303S or an QL564T by Aim-TTi, without common grounds, but then one would be looking at two to three times the cost of the rigol?
 (Power supplies taken arbitrarily from a Swiss distributor website, I checked for 3 outputs and > 195 W and the price not in the stratospheric range)

If you look at my more recent videos, I demonstrate how to fix the problem with a single wire once and for all. Also, you can install a wire externally (shorting the two common rails) if you don't want to open up the supply. Finally, in the example you cite, the current flowing to the 5V logic will be very small, so if you return the ground wire to the negative terminal corresponding to the 12V supply (i.e., channel 2 negative), then it will appear to work fine. Also, even in the worst case, when 3A is flowing, the errors introduced are quite negligble for most applications (57mV max error).

So no, there are plenty of fixes, workarounds and reasons why this isn't actually a deal-breaker.

[PioB]

Thank you very much for the information. I am still on the fence.
How well does the current limiting work, as the output capacitor is on the terminals after all the regulation circuits? With the 3633A at work, I put in 20 V, max current 20 mA, turn the output on and  connect A LED. It immediately regulates to 20 mA and the LED (or sensitive circuit) survives.
Is this a problem while operating the 832? If I understood the information from Dave's Video correctly, by the time the (I don't remember the exact capacity from the video) 1 or 10 mFD dumped its 30 Volts on the circuit, it is too late for the regulation?

I always have to remember that a 3631A is four times the cost and only delivers 1 amp on the +-25 v rails... (20 year old design with GPIB/RS232 instead of USB/LAN... The common on the high voltage channels and the isolated 6V are an advantage though.
As I said, the more I read, the less I know whether the holdups are relevant in practice or imagined... One would need to "testdrive" one