Author Topic: Changing Pots to multiturn in a 30V/3A PSU (Read 22789 times)

ym58 · « **Reply #25 on:** July 15, 2015, 03:23:29 am »

Quote from: nctnico on July 14, 2015, 08:51:16 pm

I wouldn't buy these kind of potmeters from Ebay. My experience so far has been that their range does not extend to zero. A 10k pot may have a minimum of 100 Ohms or so.

You bet !
Once I receive them, they'll be showing markings like "Boornes" or "Burns"

!!!

Quote from: JacquesBBB on July 14, 2015, 09:45:36 pm

I used a Bourns 10 turn pot that goes to zero.
The one mentioned above looks like, but if it is not certified to be a bourns pot, it is probably not.

Do you still have one of these 10-turn pots that you once salvaged to mod your PSU ?
I can buy one from you ... better trust yours than theirs !

JacquesBBB · « **Reply #26 on:** July 15, 2015, 08:23:04 am »

Quote from: ym58 on July 15, 2015, 03:23:29 am

Do you still have one of these 10-turn pots that you once salvaged to mod your PSU ?
I can buy one from you ... better trust yours than theirs !

Sorry, I do not have spare 10k 10 turn pot. Maybe you can give a try to the chinese one, but at your own risks (I buy many parts on ebay, but you have to be ready for the worst).
Otherwise
this is a good price for a genuine one
http://www.mouser.fr/ProductDetail/Bourns/3590S-2-103L/?qs=sGAEpiMZZMvygUB3GLcD7uCOAMig3YAGWQdFc%252blENJE%3d

ym58 · « **Reply #27 on:** July 15, 2015, 09:00:01 am »

Quote from: JacquesBBB on July 15, 2015, 08:23:04 am

Sorry, I do not have spare 10k 10 turn pot. Maybe you can give a try to the chinese one, but at your own risks (I buy many parts on ebay, but you have to be ready for the worst).
Otherwise
this is a good price for a genuine one
http://www.mouser.fr/ProductDetail/Bourns/3590S-2-103L/?qs=sGAEpiMZZMvygUB3GLcD7uCOAMig3YAGWQdFc%252blENJE%3d

JacquesBBB · « **Reply #28 on:** July 15, 2015, 09:34:17 am »

On ebay, they do not charge you for small items as the postage from China is per gram and very cheap. This is why they remove all packaging. Postage takes from 3 to 8 weeks to deliver.
If you order larger items, the postage can be very expensive.

Mouser sends from the US (not France) or other places by FedEX, and you receive your items in two days from the order.
Moreover, the postage is free for orders above 65 € . I always order with invoice over 65 € HT.
I usually have a backlog list of thing to order, so when I need something urgently, I fill the order with other stuff that are in my backlog list. Like that, postage is free and very fast.

ym58 · « **Reply #29 on:** July 15, 2015, 11:00:07 am »

Yes, you're right (concerning shipments from Asia).
I place orders for electronic parts nearly everyday and up to now I never "really" had to complain about quality (except sporadic resistor inversions on PCBs) nor delivery times (mostly 3-4 weeks from China mainland and 2-3 weeks from HK).

So, my guess is that I don't take much risks to order from there a pair of "Burn's" pots given their price (less than 4 USD/each, free shipping).

Actually, my asking you if you still had a spare pot handy was just to have a chance to make (small) business with another salvager frog

!

JacquesBBB · « **Reply #30 on:** July 15, 2015, 01:18:18 pm »

Quote from: ym58 on July 15, 2015, 11:00:07 am

Actually, my asking you if you still had a spare pot handy was just to have a chance to make (small) business with another salvager frog !

No problem. If you are missing any parts from your PSU, do not hesitate to ask. I have several of them. Some that I fixed, some others that I keep for parts.

ym58 · « **Reply #31 on:** July 15, 2015, 02:05:52 pm »

Good to know, thank you for proposing

I just purchased mine 63€ on Price Minister (almost new, a good deal, I think).

What I really miss on it though, is:
(a) fine tuning pots (this topic's subject)
(b) backlit LCD (I wish I could fit a few under-volted LEDs inside, but not quite sure where and how ... ?)
(c) 4 or 5-digit LCD especially for the ammeters (like those LCD described and tested by paulie here)

Any enlightenment ?

ym58 · « **Reply #32 on:** July 16, 2015, 04:07:36 am »

@JacquesBBB,

Just to keep you updated :

Apart from that, do you have any suggestion regarding points (b) and (c) mentioned in my previous post (backlit LCD and 4-5 digit LCD) ?
Thanks.

JacquesBBB · « **Reply #33 on:** July 16, 2015, 04:27:57 am »

Quote from: ym58 on July 16, 2015, 04:07:36 am

Apart from that, do you have any suggestion regarding points (b) and (c) mentioned in my previous post (backlit LCD and 4-5 digit LCD) ?

I would not recommend to do b) before c).

Both are possible. You can take the power at the 5V PSU or at the display which I think is 9V.

You can try. This is more simple than changing the pots as more accessible.

ym58 · « **Reply #34 on:** July 16, 2015, 04:39:12 am »

do you think paulie's LCD will fit inside the PSU and work straight on without having to mod any electronic (especially for the probe lines) ?

I am asking you so because you wrote that you have a few of these PSUs broken apart and I think that you can assess better than me the feasibility of such a LCD swap ...

JacquesBBB · « **Reply #35 on:** July 17, 2015, 09:44:50 am »

Is this what you want ?

For the Voltmeter, I just put it in parallel with the previous one (who do not appreciate that much. Should be better to remove it ).
For the ammeter, its more complex, but should be possible.

I am not sure its worth it on this PSU, though .

ym58 · « **Reply #36 on:** July 17, 2015, 11:05:02 am »

Actually, I'd rather have the ammeters to be 5-digit than the voltmeters, the reason being that constant current circuits generally needs to be more precise (see Lithium revitalize or charge cycles !) than constant voltage circuits (1/100 V accuracy is way sufficient).

Have you ever measured the internal resistance of the original Selectronic ammeter ?
I'll try to PM paulie to check what his are ...

JacquesBBB · « **Reply #37 on:** July 17, 2015, 11:43:16 am »

I just wanted to show you what it would look like.
I just made a temporary lousy solder to put the new display in parallel to the old one.
I confirm that is is 9V that is there for the alimentation of the display. Works fine.
I have already removed it. Just let it for the picture.

So Yes, it is possible to fit these voltmeters (these are the same as Paulie's).

I have done the study long ago for the ammeters, but do not remember. Will have to dig out, but no time now.

ym58 · « **Reply #38 on:** July 17, 2015, 12:00:25 pm »

Thanks for the info.
Concerning the ammeters : ain't no rush ... any time you get a hand on your previous studies, just let me know !

JacquesBBB · « **Reply #39 on:** July 19, 2015, 01:38:35 pm »

As it is, 10 mV corresponds to 0.16 A at the ammeter.

ym58 · « **Reply #40 on:** July 19, 2015, 01:48:52 pm »

Quote from: JacquesBBB on July 19, 2015, 01:38:35 pm

As it is, 10 mV corresponds to 0.16 A at the ammeter.

that is a mere 62.5mR impedance ... meaning that at full current capacity (3A), the voltage drop due to the serial ammeter would be around 200mV.
am I right ?

JacquesBBB · « **Reply #41 on:** July 19, 2015, 02:52:32 pm »

I just made a direct measure of the shunt resistor and found 65 mR ( with 5 mR uncertainty)

So this is it.

ym58 · « **Reply #42 on:** July 19, 2015, 03:08:03 pm »

thank you for your commitment and so precise info concerning this 30V/3A PSU !
---
all that remains for me to do now is to obtain as precise specs as yours from eBay suppliers for I guess some of them (not all, fortunately) don't even know what an impedance is

selling ammeters, swimming suits and plastic wedding rings all together does not require to be skilled in all fields ...

ym58 · « **Reply #43 on:** July 20, 2015, 12:48:52 am »

JacquesBBB,
FYI, the discussion related to PSU ammeters continues here ... you're warmly welcome to join and contribute.

FrankT · « **Reply #44 on:** July 22, 2015, 08:15:06 am »

I have a slightly different model, a Sinometer HY3005D-3, 30 volts, 5 amps.

It had the same 6.8k pots, so I replaced them with 10k multi turn. Voltage still goes up to 30v, but the current is now limited to 4.4A.

JacquesBBB · « **Reply #45 on:** July 22, 2015, 08:54:06 am »

Quote from: FrankT on July 22, 2015, 08:15:06 am

I have a slightly different model, a Sinometer HY3005D-3, 30 volts, 5 amps.

It had the same 6.8k pots, so I replaced them with 10k multi turn. Voltage still goes up to 30v, but the current is now limited to 4.4A.

I presume that if you put a 21k resistor in parallel to the pots, you will retrieve exactly the previous setting with the
same limits .

ym58 · « **Reply #46 on:** July 22, 2015, 11:41:23 am »

Quote from: FrankT on July 22, 2015, 08:15:06 am

I have a slightly different model, a Sinometer HY3005D-3, 30 volts, 5 amps.
It had the same 6.8k pots, so I replaced them with 10k multi turn. Voltage still goes up to 30v, but the current is now limited to 4.4A.

FrankT,
Which pots did you change with multiturn-10K's : Current, Voltage or both ?
Coz JacquesBB's tweak to parallel then with a 21K resistor to drop the impedance down to 6.8K should normally affect (improve) the pots' linearity only.
I am a bit surprised it has now limited the current output ...

FrankT · « **Reply #47 on:** July 24, 2015, 09:11:12 am »

Quote from: ym58 on July 22, 2015, 11:41:23 am

Quote from: FrankT on July 22, 2015, 08:15:06 am
I have a slightly different model, a Sinometer HY3005D-3, 30 volts, 5 amps.
It had the same 6.8k pots, so I replaced them with 10k multi turn. Voltage still goes up to 30v, but the current is now limited to 4.4A.
FrankT,
Which pots did you change with multiturn-10K's : Current, Voltage or both ?
Coz JacquesBB's tweak to parallel then with a 21K resistor to drop the impedance down to 6.8K should normally affect (improve) the pots' linearity only.
I am a bit surprised it has now limited the current output ...

I changed both.

I didn't notice the change to the maximum current until after I had reassembled the unit. Then it was a case of "meh, it will do for now". I will try a parallel resistor if I ever take it apart again.

ym58 · « **Reply #48 on:** July 24, 2015, 11:30:38 am »

Quote from: FrankT on July 24, 2015, 09:11:12 am

I didn't notice the change to the maximum current until after I had reassembled the unit. Then it was a case of "meh, it will do for now". I will try a parallel resistor if I ever take it apart again.

Meh, I can understand

...
The real need to have a 5A PSU and not a limited 4.4A is not that crucial ...
HOWEVER, the point is to be sure that the current indication is reliable since you changed the pots !
Did you crosscheck it with another ammeter (one outside of the PSU box) ?

FrankT · « **Reply #49 on:** July 25, 2015, 03:21:13 am »

Quote from: ym58 on July 24, 2015, 11:30:38 am

The real need to have a 5A PSU and not a limited 4.4A is not that crucial ...
HOWEVER, the point is to be sure that the current indication is reliable since you changed the pots !
Did you crosscheck it with another ammeter (one outside of the PSU box) ?

Good point. I just checked it and the indicated current is within 20mA.


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Author Topic: Changing Pots to multiturn in a 30V/3A PSU (Read 22789 times)

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