Questions on my "new" Array 3720A - Page 1
Forum section: electronics / testgear

author: motocoder
author_rank: Unknown
timestamp: July 12, 2014, 07:19:32 am
content: I recently purchased an Array 3720A Electronic Load from a seller on eBay. The item was listed as new, and was about $150 - $200 less than I could get it for anywhere else. It appears the seller actually sold several of these in the same listing.It arrived today, and based on the box, the fact that the calibration certificate listed a calibration date in 2012 (and that expired in 2013), the unit is clearly not new by most people's definition of the word. It is possible that it is unused, although the fact that it wasn't in a box with the manufacturers name on it makes me a bit suspicious of that.All that said, I'll probably keep the unit if it is functioning correctly. As long as it works, it's just not worth the hassle to return. But I really want to be thorough about confirming that it is working correctly.So first question I have, for others with Array units: What do the fans sound like? This one has a very load fan noise, and the fan has sort of a whine sound to it. Is that normal?Second question: The unit has RS-232 and GPIB, but no USB. Is it possible to replace the GPIB board with USB, and if so, where would I go to purchase the USB option? Is it worth the cost of the USB interface board, or just connect up a USB->Serial datapter to it (i.e., is there a speed difference)?Third question: What sort of tests would you recommend to verify correct operation? I did connect it up to my Agilent power supply and I let it run at a 120W power level for a few hours. I tested out a number of the different operating modes, and I don't see anything obviously wrong with it, but perhaps there are some other tests I should do?Thanks

author: nctnico
author_rank: Super Contributor
timestamp: July 12, 2014, 12:11:23 pm
content: My 3710A loads also have loud fans. Fortunately they only turn on when the unit gets too warm.

author: motocoder
author_rank: Unknown
timestamp: July 12, 2014, 03:23:16 pm
content: Quote from: nctnico on July 12, 2014, 12:11:23 pmMine come on as soon as I power the unit on...

author: msquared
author_rank: Regular Contributor
timestamp: July 13, 2014, 05:31:45 am
content: I bought a new 3720A a months ago and was surprised to find out that the fans come on with the power and run at full speed regardless of load.They are loud and have a pretty unique annoying whine/rattle to them also they sound pretty close to a jet engine spinning down when the unit is turned off.But despite the noise I've been very happy with it, I just don't leave it on any longer than necessary.I did think about trying to isolate the fans from the case or improve the airflow to at least try to get rid of the rattle and maybe change the pitch of the whine but after opening the case I didn't really feel like tearing into the way Array had mounted the fans in a little wind tunnel around the heat sinks. hmmm.... Maybe later.Here's a pic of the fans in my 3720.

author: motocoder
author_rank: Unknown
timestamp: July 14, 2014, 05:32:50 am
content: Quote from: msquared on July 13, 2014, 05:31:45 amThank you. I feel better at least knowing the fan noise is normal. Except for being a little out of calibration, and a GPIB interface instead of the USB that I would prefer, the unit seems great.BTW - what do you use to connect to those strange connectors? I would have preferred banana connectors, but these units all seem to expect someone to shove a raw wire in a hole and tighten down a clamp.

author: PedroDaGr8
author_rank: Super Contributor
timestamp: July 14, 2014, 05:47:54 am
content: Quote from: motocoder on July 14, 2014, 05:32:50 amSpade connectors, these loads expect higher currents than I think most Banana plugs are rated for.

author: nctnico
author_rank: Super Contributor
timestamp: July 14, 2014, 09:37:13 pm
content: Hirschmann PK110 4mm 'banana' posts are rated for 35A. I replaced the terminals on one of my 3710 loads with these.

author: motocoder
author_rank: Unknown
timestamp: July 18, 2014, 01:15:19 am
content: Any of you chaps been able to update the firmware in this beastie? I can't get their firmware update program to work. It gives me a variety of errors. Seems the same genius that wrote their remote control software also wrote this one.

author: saturation
author_rank: Super Contributor
timestamp: July 18, 2014, 05:23:13 pm
content: Some comments:I own and use my 3710a fairly often. It has 4 fans, bottom come on first and its quiet even when they are on. The rear fans supplement bottom fans as needed. Each fan has its own thermal sensor, and triggers on its own IIRC, as needed.4 fans with each having a thermal sensor is a lot of redundancy, unusual to have such a design in Chinese hardware.When I work on 50W and under, bottom fans rarely come on. 100W and up the bottom fans are on all the time, and the rear fans, as needed. at > 150W, all fans are blowing continuously.The feed-through stud or junction block style connectors are better for high current applications and safety; if a banana jack is pulled off accidentally it can spark; as a banana jack ages the connection integrity could weaken and cause small resistances that could heatup; debris could enter the jack while bolt studs are easy to clean and care for, and the torque can be adjusted for optimum connections each time even as the connectors age; the state and extent of the connectionis fully visible to the operator.To test your eload just cycle it through all its capabilities written in the published specifications. If you are short on time, just a max load test and check internal temps is enough; good thermal management should keep the heatsinks close to 50C, and closer to 100C the more problematic it is.Enjoy!

author: motocoder
author_rank: Unknown
timestamp: July 19, 2014, 01:26:05 am
content: Quote from: saturation on July 18, 2014, 05:23:13 pmIt's strange that the 3720 doesn't have as sophisticated a thermal management design. My fans just run full speed all the time. I thought that the 372x series was superior in every way to the 371x...

author: saturation
author_rank: Super Contributor
timestamp: July 19, 2014, 01:19:38 pm
content: Its probably more about saving money on hardware cost by removing redundant elements and simplifying thermal management. It will still do the job at lower cost, and suffer the ergonomicsAs to saving money in making the 371xa today, they could cut down the redundant parts, but I guess they have a successful formula, so why change it now?Quote from: motocoder on July 19, 2014, 01:26:05 am