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Products => Test Equipment => Topic started by: Jay_Diddy_B on October 14, 2020, 10:26:52 pm

Title: ACME PS2L-1000 - 1000W Electronic Load Teardown
Post by: Jay_Diddy_B on October 14, 2020, 10:26:52 pm

Hi,

There is a lot of interest in electronic loads. I am going to share some pictures of an Acme PS2L-1000 load that I was working on.

This load is 60V Max, 110A Max, 1kW Max

This load is about 40 years old, but it shows how the load was constructed. I had the unit apart for cleaning and electrolytic capacitor replacement. The load will work in constant current and / or constant resistance modes.

Manual

The manual can be found here:

http://userequip.com/files/specs/3577/ACME%20PS2L-500,%20PS2L-1000%20Operating%20&%20Troubleshooting%20Guide.pdf (http://userequip.com/files/specs/3577/ACME%20PS2L-500,%20PS2L-1000%20Operating%20&%20Troubleshooting%20Guide.pdf)

The manual contains partial schematics.

Pictures

[attachimg=1]
(https://www.eevblog.com/forum/testgear/acme-ps2l-1000-1000w-electronic-load-teardown/?action=dlattach;attach=1089508;image)

The leads are long enough to allow the front panel to be laid down.

[attachimg=2]
(https://www.eevblog.com/forum/testgear/acme-ps2l-1000-1000w-electronic-load-teardown/?action=dlattach;attach=1089512;image)



This shows the back of the front panel.

Heatsink assembly

[attachimg=3]
(https://www.eevblog.com/forum/testgear/acme-ps2l-1000-1000w-electronic-load-teardown/?action=dlattach;attach=1089516;image)

[attachimg=4]
(https://www.eevblog.com/forum/testgear/acme-ps2l-1000-1000w-electronic-load-teardown/?action=dlattach;attach=1089520;image)

The heatsink assembly can be removed, for maintenance. The transistors are electrically connected to the heatsink. The heatsink doubles as the positive bus bar.
There is a large stud diode and stud SCR. These are for reverse polarity and Over-voltage protection. They will blow the 130A fuse.

Transistor Details

There are nine T0-3 transistor on each heatsink:

[attachimg=5]
(https://www.eevblog.com/forum/testgear/acme-ps2l-1000-1000w-electronic-load-teardown/?action=dlattach;attach=1089524;image)

The transistors are mounted in sockets. Each transistor has 0.4 \$\Omega\$ emitter resistor.
There is no shunt. The current is measured by averaging the voltage across all the emitter resistors.

[attachimg=6]
(https://www.eevblog.com/forum/testgear/acme-ps2l-1000-1000w-electronic-load-teardown/?action=dlattach;attach=1089528;image)

[attachimg=8]
(https://www.eevblog.com/forum/testgear/acme-ps2l-1000-1000w-electronic-load-teardown/?action=dlattach;attach=1089538;image)

There are 34 transistors, that is 1000/34 = 29W per transistor.

Control Board

Here is a picture of the control board. It is a single sided board. I will replace the electrolytic capacitors.

[attachimg=7]
(https://www.eevblog.com/forum/testgear/acme-ps2l-1000-1000w-electronic-load-teardown/?action=dlattach;attach=1089532;image)

Regards,
Jay_Diddy_B

Title: Re: ACME PS2L-1000 - 1000W Electronic Load Teardown
Post by: Jay_Diddy_B on October 21, 2020, 02:10:10 am

Hi,

I have replaced the electrolytic capacitors on the control board:

[attachimg=1]
(https://www.eevblog.com/forum/testgear/acme-ps2l-1000-1000w-electronic-load-teardown/?action=dlattach;attach=1094320;image)


Capacitors used

Code: [Select]

ACME PS2L-1000 Capacitors					
					
Digikey	QTY	Description	MFG	MFG No	Notes
					
1572-1126-ND	2	CAP ALUM 330UF 20% 50V AXIAL	Illinois Capacitor	337TTA050M	
4050PHCT-ND	1	CAP ALUM 150UF 20% 40V AXIAL	Vishay Beyschlag/Draloric/BC	MAL202137151E3	
4023PHCT-ND	1	CAP ALUM 1000UF 20% 16V AXIAL	Vishay Beyschlag/Draloric/BC	MAL202190518E3	was 820uF
56-MAL203038228E3CT-ND	4	CAP ALUM 2.2UF 63V AXIAL	Vishay Beyschlag/Draloric/BC	MAL203038228E3	
					

I did my best to match the sizes of the originals. It some cases it meant that I had to go to a higher voltage.


Regards,
Jay_Diddy_B

Title: Re: ACME PS2L-1000 - 1000W Electronic Load Teardown
Post by: bnetz on April 24, 2024, 08:01:17 pm

Thanks for the great write up! Do you have a working link to the manual? I recently got one and plan on refurbing it

Title: Re: ACME PS2L-1000 - 1000W Electronic Load Teardown
Post by: Phil1977 on April 25, 2024, 01:18:56 pm

One maybe stupid question about big electronic loads: Why does it seem all commercial electronic loads use power transistors to dissipate everything?

In DIY-loads I usually diverted a DC-DC converter from its original use by modification of the control loop. In the end I had a DC-DC-converter that "sends" a controllable amount of power to an external dissipation device like a water kettle or incadescent lamp.

By this setup, you only need a high quality heatsink for the switching losses of the converter - the major part of the load power can be wasted in a part that can be much hotter or is easier to cool by e.g. boiling water. Sometimes I even used an e-bike battery as a "waste device" so that in the end the energy was not lost at all.

Maybe you could even connect a micro inverter like it´s used for small domestic PV-generators and recycle the power to the AC-grid.

PS: A little googling showed that many larger scale battery test loads nowadays backfeed into mains. Would have been to strange if no one else would have had this idea  :phew: