Author Topic: Amrel EL1132 Teardown  (Read 3612 times)

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Offline amc184

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Amrel EL1132 Teardown
« on: April 19, 2015, 05:35:38 am »
I'm surprised I haven't seen a thread on this already.  I bought one of the notorious $89 loads from eBay, and was one of the people who were lucky and got one.  Mine seems to have been manufactured in 1997, so it's weird that it sat around in its box until 2014 before being resold by a surplus outlet.

My one works nicely, apart from having a small (~-45mA) fixed current offset.  I might try and recalibrate it at some stage, but it will be a bit of a hassle to get together everything required.  It's a good instrument with a lot of features.  The stand out feature for me is the ability to set the slew rate on programmed transients.  So not only can you tell the supply to switch between a load of 1 and 2A at 10Hz, but you can tell it to change between those two currents at a rate of 500mA/us.  Lots of loads don't have that.





It's constructed of folded steel sheet, with a mainboard taking up most of the base of the chassis.  The power is dissipated into an aluminium tunnel heatsink with fans at both ends (fairly loud when on, not temperature controlled).  Two riser boards plug into the mainboard, a DAC board and a CPU board.  The power transformer is chassis mounted at the front of the unit.







Each IRFP250 MOSFET seems to be part of a local loop, each has its own AD712 dual opamp and shunt.   The shunt is made up of a large loop of enameled wire about 2.9mm in diameter, possibly copper, but possibly something with a better temperature coefficient.

Right side:



Left side:

This image shows the area where I found a really bad assembly defect with my unit.  The GPIB ribbon cable (wide, grey, far left in image) was folded wrong and pressed hard into the back of the IEC connector.  Nothing was punctured, but the insulation on the GPIB cable isn't mains rated, and could have worn through over time.  A short between the GPIB interface and mains could be an injury hazard, and well as being catastrophic for the unit and a connected GPIB controller.  Easy to fix though.



The front of the mainboard has the power supply.  It's pretty simple, a couple of rectifiers, smoothing capacitors and linear regulators.  Despite the huge heatsink, this unit doesn't actually need much power of its own to run.  There will be two isolated supplies in this unit, an earthed outguard supply for the CPU and GPIB sections, and a floating inguard supply for the actual load.  There's no electrical connection between the two.



The larger riser board mainly contains the DACs that drive the load.  There seems to be four channels, I'm not sure if they each drive a pair of loads, or some other configuration.  This load has two ranges (6A and 60A), and I suspect the reed relays scattered throughout the unit may be for range switching.  Here's descriptions for the key components:

Analog Devices AD711 and AD712 precision FET input single / dual opamp
Kuan Hsi D1A050000 SPST reed relay
Analog Devices AD7541A 12-bit parallel input R2R DAC
Mitsubishi M5M81C55P 2kb static RAM
NEC µPD71055C port expander
Texas Instruments LM339 quad comparator
National Semiconductor LM393 dual comparator
GAL16V8 8 macrocell PLD
Temic TSC80C31 8-bit microcontroller
NEC µPD71054C programmable timer / counter
Kodenshi K4N35 optocoupler
plus assorted glue logic and an EPROM

This board also must contain an ADC, since the unit is able to read back what current it's actually sinking.  It's probably got a slope ADC using some of the comparators together with the µPD71054 counter.



The smaller riser board contains the controller and PC interface.  Here's descriptions for the key components:

Linear Technology LT1054 regulated switching voltage converter
Z80180 8-bit microprocessor
Sony CXK5864 8kB static RAM
GAL16V8 8 macrocell PLD
Atmel AT93C46 1kb serial EEPROM
National Instruments NAT7210 GPIB interface
plus assorted glue logic and an EPROM

Pretty standard stuff for a 90s design.  The two riser boards would be vastly simpler if redesigned today.



« Last Edit: April 19, 2015, 05:37:29 am by amc184 »
 

Offline mtdoc

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Re: Amrel EL1132 Teardown
« Reply #1 on: April 19, 2015, 06:22:27 am »
Nice teardown and photos. Thanks.

I bought one of these as well. It's the first electronic load I've used and so far have I've only used it to do some basic power supply and battery testing. I've barely tapped into its capabilities. I'd really like to find a copy of the full user manual.  I have not been able to figure out how to use the front keypad to access all of its functions, though I'm sure this is due to my own ignorance about using electronic loads.
 
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Offline Stan Best

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Re: Amrel EL1132 Teardown
« Reply #2 on: October 06, 2020, 02:09:46 pm »
Hi there, if you are still around. We bought an EL 1132 new in the 90s, still got it and it has never ever had any issues. If only i could say the same for organisation in our lab.
We have really irretrievably lost the manual and need to write some code to control it via the GPIB buss . Some time spent trying every search avenue has failed to find an online copy either. I have emailed AMETEK parts, but it don't hold out much hope.
If anyone on here has still got the manual and can help that would be fantastic. I have no idea how you would get the information to us but its for the company so any expenses can be covered. 
 

Offline philpem

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Re: Amrel EL1132 Teardown
« Reply #3 on: October 07, 2020, 07:09:04 am »
Hi there, if you are still around. We bought an EL 1132 new in the 90s, still got it and it has never ever had any issues. If only i could say the same for organisation in our lab.
We have really irretrievably lost the manual and need to write some code to control it via the GPIB buss . Some time spent trying every search avenue has failed to find an online copy either. I have emailed AMETEK parts, but it don't hold out much hope.
If anyone on here has still got the manual and can help that would be fantastic. I have no idea how you would get the information to us but its for the company so any expenses can be covered.

There's another thread about these DC loads here which might be of help: https://www.eevblog.com/forum/buysellwanted/dc-load-on-ebay-89-dollars/?all

The Dropbox link in that thread goes to a programming manual and still works as of this morning. Unfortunately it's too big to attach to this post :(

I contacted Ametek back in 2014 and they told me that they had no information on the EL-1132. It dates back to around 1998.

If you do find a complete user's manual, I'd be very interested in a copy.

Thanks
Phil.
Phil / M0OFX -- Electronics/Software Engineer
"Why do I have a room full of test gear? Why, it saves on the heating bill!"
 

Offline Stan Best

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Re: Amrel EL1132 Teardown
« Reply #4 on: October 07, 2020, 08:58:07 am »
Perfect, the programing and cal info was still there and all safely in a shared Dropbox folder here now.
In the meantime we did get moving by getting lucky with the serial commands in another manual. A bit scary but it worked.
Wouldn't it be nice to get kit engineered like those Eloads today? Our unit has done about 10 years in goods in on QA and gets powered up maybe twice a year in the lab. We did pay full price back in the day.
 


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