Author Topic: Looking for a DC load  (Read 2538 times)

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Online BillB

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Re: Looking for a DC load
« Reply #25 on: April 11, 2018, 12:58:19 am »
The B&K website tells me that Itech is somehow associated with them or a subsidiary, which isn't bad news at all. The manual does mention SCPI, but leaves the exact commands undocumented. I don't think SCPI is standarized enough to just be able to jump in. Let's see if I can dig up more.
There we go: http://www.itechate.com/Upload/File/20150806155656.pdf

Good find. 

There are some threads here discussing the relationship between BK/ITech/Maynuo.  Apparently, the design is from the same primary designer moving to different companies.  We have BKs at work, but for the home/hobbiyist, I'm perfectly comfortable with ITech's quality vs BK given it is a fraction of the price.

The only problem is that for the voltage, you'd need to step up to the XX12B versions, and the Maynuo is cheaper than the corresponding ITech, but I don't know if the older Maynuo supports SCPI.  Now you're in the $500+ price range which opens the door to alternatives like the Array 3723A mentioned by @MarkL.

 
« Last Edit: April 11, 2018, 01:00:02 am by BillB »
 

Offline David Hess

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Re: Looking for a DC load
« Reply #26 on: April 11, 2018, 08:56:41 am »
However there are two issues that lead to me to looking at other alternatives. Most Maynuo models only go up to 150V. Normally I don't work with anything near that, but I can imagine wanting to work on nixie tube power supplies in the future. Considering these are typically 160V to 170V, the aforementioned models won't do. The M9812B solves the voltage problem, but this doubles the cost of the unit and I'm not sure the added benefit is worth that.

If it is that close, I might put a 40 volt shunt regulator (precision power zener diode) in series with the load and use a small preload to keep the shunt regulator operating correctly with no load from the DC load.  Of course now you cannot pull the load down below 40 volts.

 
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Online Mr. Scram

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Re: Looking for a DC load
« Reply #27 on: April 11, 2018, 10:34:27 am »
I like the Array 3723A.  Max envelope is 200V, 30A, 350W.  The CC, CP, CR, CV loop response is excellent.

  http://www.array.sh/yq-3721e.htm

It has sense inputs, and they're on the front which is very much appreciated (but not standard spacing, oops).

It speaks SCPI via an isolated RS232 port (no ridiculous converter dongle), and has an optional GPIB card, which I have on my units.

The fans are variable speed.

The quality is surprisingly good.  I bought two of them after evaluating B&K and TTI.  The only downside is it's higher than your stated price target @ USD$769.  There are some other models in their 372x series at higher and lower prices.  Here's one distributor with posted pricing and discounts:

  https://www.circuitspecialists.com/programmable-dc-electronic-loads
The price of the 200V Array 3722A model actually looks interesting, but that one's much more expensive elsewhere. I don't think I'm prepared to spend >600 euro on a DC load right now.
 

Offline bicycleguy

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Re: Looking for a DC load
« Reply #28 on: April 11, 2018, 11:47:41 am »
I like the Array 3723A.  Max envelope is 200V, 30A, 350W.  The CC, CP, CR, CV loop response is excellent.

  http://www.array.sh/yq-3721e.htm

It has sense inputs, and they're on the front which is very much appreciated (but not standard spacing, oops).

It speaks SCPI via an isolated RS232 port (no ridiculous converter dongle), and has an optional GPIB card, which I have on my units.

The fans are variable speed.

The quality is surprisingly good.  I bought two of them after evaluating B&K and TTI.  The only downside is it's higher than your stated price target @ USD$769.  There are some other models in their 372x series at higher and lower prices.  Here's one distributor with posted pricing and discounts:

  https://www.circuitspecialists.com/programmable-dc-electronic-loads
That looks nice.  Trying to research a little found this guy a while back complaining about input capacitance of the Array 3711A:
http://www.eevblog.com/forum/testgear/digital-load-recommendations/msg1367620/#msg1367620
I don't understand how this could be.  How could you do transients and pulses?  I realize it's a cheaper model.  Any comments?

Also looking at the manual for the 372x series I have a question.  What happens on your 350W model if you setup say 20A and put in 36V=720W.  I think it says it current limits after a time period?  What does that mean exactly?  Can it handle higher watts for a short time?
 

Online MarkL

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Re: Looking for a DC load
« Reply #29 on: April 12, 2018, 03:51:17 am »
...
Trying to research a little found this guy a while back complaining about input capacitance of the Array 3711A:
http://www.eevblog.com/forum/testgear/digital-load-recommendations/msg1367620/#msg1367620
I don't understand how this could be.  How could you do transients and pulses?  I realize it's a cheaper model.  Any comments?
The 3723A has 2.2uF in series with 3 ohms across the terminals (measured with an LCR meter; I didn't open the unit).  It hasn't gotten in my way for anything I needed.  However, if for example, you were doing CV transients with low load currents it could be a factor.

The 150uF forrestc is mentioning in the 3711A is approaching two orders of magnitude larger.  I would probably have his same complaints in scenarios with rapidly changing voltages across the input terminals.  If you were doing purely current transients/pulses with little to no change in voltage I would think the input capacitor would not be a major factor.

In that thread they are also saying the 3711A is a rebadge.  I don't think the 3723A is, or at least I've never seen one branded differently.  It seems to be a new/different design than the 371x series.

Quote
Also looking at the manual for the 372x series I have a question.  What happens on your 350W model if you setup say 20A and put in 36V=720W.  I think it says it current limits after a time period?  What does that mean exactly?  Can it handle higher watts for a short time?
A quick test with a 60V 9A supply shows that it will sustain 369W for at least 3 minutes (that's how long I waited), and anything at or above 370W for 5 seconds with current limiting to keep it under 410W.  After 5 seconds the overload protection turns off the input and needs to be manually reset.

But I should add this is hardly an exhaustive test and there may be other edge cases on how it decides to do the protection.
 
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Online Mr. Scram

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Re: Looking for a DC load
« Reply #30 on: April 12, 2018, 03:53:17 am »
If it is that close, I might put a 40 volt shunt regulator (precision power zener diode) in series with the load and use a small preload to keep the shunt regulator operating correctly with no load from the DC load.  Of course now you cannot pull the load down below 40 volts.
That's an interesting thought. I haven't been able to come up with another case the past few months that requires a higher voltage and I doubt I'll be deep into nixies any time soon. The solution is a little finicky, but it does mean buying an affordable load without worrying too much about edge use cases that are out of reach.
 

Offline David Hess

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Re: Looking for a DC load
« Reply #31 on: April 14, 2018, 06:39:37 am »
If it is that close, I might put a 40 volt shunt regulator (precision power zener diode) in series with the load and use a small preload to keep the shunt regulator operating correctly with no load from the DC load.  Of course now you cannot pull the load down below 40 volts.

That's an interesting thought. I haven't been able to come up with another case the past few months that requires a higher voltage and I doubt I'll be deep into nixies any time soon. The solution is a little finicky, but it does mean buying an affordable load without worrying too much about edge use cases that are out of reach.

It is what I did in the past when faced with the same conundrum.  Ordering $20 worth of big zener diodes or power transistors (or both) to make what is essentially a shunt voltage regulator or precision power zener diode was a lot more palatable then buying or even renting a DC load for what was likely a one time test.

If the required power dissipation (of the shunt) is not too high and the precision is adequate, then some inexpensive power zener diodes may be suitable.  If high frequency performance must be preserved, then bypass the zener diodes or precision shunt regulator with capacitors.
 

Offline bicycleguy

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Re: Looking for a DC load
« Reply #32 on: April 14, 2018, 07:56:42 am »
Mr Scram,
Don't want to hyjack your thread but you seem to be vague about what you want and I am clueless so would an e-load work for these use cases or more specifically how good and what spec e-load:

1.  Making VI curves of a 300W max, 40V open circuit, 9.7A short circuit  solar panel.

2.  Designing, testing and debugging a MPPT (max power point tracking) DC-DC converter for above panel.

For the MPPT task would it introduce more problems for a noob than using resistor banks?
 

Offline woody

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Re: Looking for a DC load
« Reply #33 on: May 02, 2018, 10:00:16 pm »
I like the Array 3723A.  Max envelope is 200V, 30A, 350W.  The CC, CP, CR, CV loop response is excellent.

  http://www.array.sh/yq-3721e.htm

It has sense inputs, and they're on the front which is very much appreciated (but not standard spacing, oops).

It speaks SCPI via an isolated RS232 port (no ridiculous converter dongle), and has an optional GPIB card, which I have on my units.

The fans are variable speed.

The quality is surprisingly good.  I bought two of them after evaluating B&K and TTI.  The only downside is it's higher than your stated price target @ USD$769.  There are some other models in their 372x series at higher and lower prices.  Here's one distributor with posted pricing and discounts:

  https://www.circuitspecialists.com/programmable-dc-electronic-loads
The price of the 200V Array 3722A model actually looks interesting, but that one's much more expensive elsewhere. I don't think I'm prepared to spend >600 euro on a DC load right now.
Yesterday I got a 3721A from

https://labtronix.co.uk/drupal/shop/electronicload/el3723a

With USB interface, shipping and Paypals' stiff exchange rate it translated to €589,- ex. VAT.

If you leave off the USB interface I recon that the 3723A will cost about the same, just under €600,-

Not affiliated and I do not have the device yet, so cannot tell you more than that he guy running the shop is responsive.
 
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Offline colorado.rob

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Re: Looking for a DC load
« Reply #34 on: May 07, 2018, 01:34:02 pm »
Who sells itech in the US?  I'm looking for the IT6400 series, and only seen them available in Europe and AU.
 

Online BillB

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Re: Looking for a DC load
« Reply #35 on: May 08, 2018, 02:00:06 am »
Who sells itech in the US?  I'm looking for the IT6400 series, and only seen them available in Europe and AU.

Tequipment.net carries ITech but I don't see the 6400s.  Maybe contact them to see if they can get one?
 


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