Picked up a CSI1802X bench supply ($50, 0-18v, 0-2A)

[cellularmitosis]

I saw this supply online for $50 and after seeing a couple of tear-downs and finding the schematic, I just couldn't resist.  I've got a few mods planned for this little guy

Website: http://www.circuitspecialists.com/bench-power-supply-csi1802x.html

Schematic: http://www.circuitspecialists.com/pdf/1802X_schematic.pdf

Previous forum thread: https://www.eevblog.com/forum/chat/insides-of-a-0-18v-2a-power-supply-the-csi1802x/

Tear-down I found on a blog of a similar model: http://pickandplace.wordpress.com/2012/06/08/qj1502c-15v-2a-power-supply-review-labornetzgerat-test-mastech-hy1502d/

[c4757p]

I see they fixed some of the problems my identical-looking Mastech version had. Interestingly, that includes the frequency compensation networks. Glad I never found the problem with those...

[cellularmitosis]

First, a worst-case thermal test (leads shorted, amperage knob all the way up).

The hottest point I could find by probing with a type-k thermocouple was the head of the screw which secured the pass transistor to the heat sink.

Ambient temp at the time of test was 23C.

At the 5-minute mark, the pass transistor screw measured 72C.

At the 10-minute mark, the pass transistor screw had climbed to 82C.

I also measured the bridge rectifier (four discrete 3 amp diodes), which read quite a bit hotter at 93C (this surprised me a bit).

There was another transistor (a TO-220 D880Y) which read 68C.

I also measured the transformer case, but it was only 33C.  After powering it down I felt the transformer to confirm, and it seemed very mildly warm.

[c4757p]

At the 5-minute mark, the pass transistor screw measured 72C.

At the 10-minute mark, the pass transistor screw had climbed to 82C.

I see the 65°C thermal cutoff switch in the schematic is just for show.

[cellularmitosis]

One thing I really liked about this supply was the 1mA readout.  However, the single-turn pots are totally hopeless for dialing in an exact value.

Keeping in the spirit of the cheapest possible power supply, I gave it a little upgrade using the cheapest possible 10-turn pots.  Luckily they fit precisely into the existing holes, and they just barely fit next to the circuit board.  No drilling required!

This was a huge improvement in usability.  Now, I can dial in 20mA through an LED relatively easily.

One thing to watch out for: all of the screws are self-tappers directly into the plastic or sheet metal, so it is extremely easy to strip them out while performing mods like this.

edit: spelling

[cellularmitosis]

(Apologies for the incorrectly rotated photos, they are all rotated correctly when viewed on my laptop, so I'm not sure what I can do to fix that situation...)

[cellularmitosis]

On second thought, the relay for the second tap kicks in around 6.6V.  I wonder if using a dummy load to draw 2A at the bottom of the second tap (6.6V) would be even more of a worst-case scenario for heat?  (18v-6.6v * 2A should be greater than 6.6v-0v * 2A, right?).

[GeoffS]

(Apologies for the incorrectly rotated photos, they are all rotated correctly when viewed on my laptop, so I'm not sure what I can do to fix that situation...)

It seems to be a forum thing. If I download the images and view them they are the right way around.

[c4757p]

(Apologies for the incorrectly rotated photos, they are all rotated correctly when viewed on my laptop, so I'm not sure what I can do to fix that situation...)

It seems to be a forum thing. If I download the images and view them they are the right way around.

If they were taken with a phone - many (most? all?) don't actually rotate the image when you rotate the phone, they just stuff a tag in the EXIF data. Some viewers respect that tag and others don't.

[GeoffS]

Spot on. Images taken with an iPhone 4
They have the OP's GPS coordinates too 

[BravoV]

Spot on. Images taken with an iPhone 4
They have the OP's GPS coordinates too 

Missile location locked on.... 

[GeoffS]

Spot on. Images taken with an iPhone 4
They have the OP's GPS coordinates too 

Missile location locked on.... 

Nice looking place but a bit close to the freeway 

[Napalm2002]

I'm going to buy one of these power supply's. Can u give me the part numbers and where u purchased the upgraded pots?

[cellularmitosis]

Before you order the super cheap parts, keep in mind that I have been warned by other forum members that they are junk.  I will not be surprised if these fail in a month, but I'm ok with that, as I know not to use this supply to power anything expensive or precious.

Search ebay for "wxd3-13 10 turn".  You don't really save much until you order in quantities of ten (at which point they are $1.50 each).

[Monkeh]

Those pots are okay so long as you're exceedingly careful handling them and soldering.

[Napalm2002]

How many ohms? Is there a better source? Maybe a ill more expensive and more quality version? Of the ten turn pots I mean?

[Pasky]

Wow thank you for all this information, I'm tempted to grab one myself for $50.  I don't need anything over 12V, 1.5A anyways.

Before I pull the trigger, is there anything better within the same price range?

EDIT:

Actually, I just saw this:

http://www.circuitspecialists.com/csi3003sm.html

http://blog.circuitspecialists.com/product-review-of-the-csi3003sm-and-csi3005sm-dc-switching-power-supplies

0-30V, 0-3A.  Thoughts?

[rdl]

That is a switch mode power supply. Check the ripple spec. Okay if you can live with 200 mV p-p

Wow thank you for all this information, I'm tempted to grab one myself for $50.  I don't need anything over 12V, 1.5A anyways.

Before I pull the trigger, is there anything better within the same price range?

EDIT:

Actually, I just saw this:

http://www.circuitspecialists.com/csi3003sm.html

http://blog.circuitspecialists.com/product-review-of-the-csi3003sm-and-csi3005sm-dc-switching-power-supplies

0-30V, 0-3A.  Thoughts?

[Pasky]

Ah yes, a switching regulator would cause too much noise for what I would be needing this for, thanks for pointing that out.

I think I'll grab the linear in the original post.  They have another one for $80 that does 0-30V and 5A, but I don't think I'll need anything for the small things I do. 

Can anyone suggest some quality multi turn potentiometers for the knobs?  I don't wanna install something that will just fail within a few months  Thanks.

[mariush]

Have a look at Digikey, Mouser, Newark for some good ones:

Digikey: http://www.digikey.com/product-search/en?FV=fff40004%2Cfff80335%2C5c0007&mnonly=0&newproducts=0&ColumnSort=1000011&page=1&stock=1&pbfree=0&rohs=0&quantity=&ptm=0&fid=0&pageSize=25

Newark : http://www.newark.com/webapp/wcs/stores/servlet/Search?catalogId=15003&langId=-1&storeId=10194&categoryId=800000005295&sort=P_PRICE&pageSize=25&showResults=true&sf=502,783&pf=810046862

Mouser : you'll have to look, I don't visit this one often, but they sometimes have better prices than Digikey.

[Napalm2002]

Can anyone tell me what the values are for the two pots? I would like to upgrade to decent ten turn pots. Can anyone tell me what the resistance values are so I can order quality pots.


Mike m

[Pasky]

From the pictures, they say 10K

[Napalm2002]

I guess that my dumbass should have zoomed in on the pictures!
Good looking out Pasky


Mike m

[Napalm2002]

Just ordered one, can't wait to get it and play with it!