electronic load amp/voltmeter conections

[tekguy]

hi all i have built a chineese xiaolin 150watt electronic load kit,its this one:https://www.aliexpress.com/item/33020512009.html?spm=a2g0o.detail.1000014.11.670448bfQSkNIe&gps-id=pcDetailBottomMoreOtherSeller&scm=1007.40000.267768.0&scm_id=1007.40000.267768.0&scm-url=1007.40000.267768.0&pvid=70a52b99-2e4a-4c21-a055-d4a60c9797b3&_t=gps-id:pcDetailBottomMoreOtherSeller,scm-url:1007.40000.267768.0,pvid:70a52b99-2e4a-4c21-a055-d4a60c9797b3,tpp_buckets:668%232846%238116%23972&pdp_ext_f=%7B%22sku_id%22%3A%2267162119657%22%2C%22sceneId%22%3A%2230050%22%7D&pdp_npi=2%40dis%21GBP%2110.24%219.21%21%21%21%21%21%40211b442116636081784537432e5d6e%2167162119657%21rec
does anyone know whats with the conections they are on about?,i want to connect a chineese volt/amp meter to it but what the ali page says totaly confuses me.

[ledtester]

The connections are:

IN +/-: power supply being tested
A +/-: connections for an ammeter - note A- is the same as IN-
V +/-: same as IN +/- to be used to connect a voltmeter

For instance, you could put a multimeter measuring current across A +/-. If you do not use an ammeter then you must short A+ to A-.

For one of those volt/amp panel meters with a thick red and black pair and a thin yellow wire, you should connect:

- black to A-
- red to A+
- yellow to V+

[tekguy]

cheers for that,whats the waffle on there aliexpress add any idea?,something about a diode.

[ledtester]

The diode(s) aren't needed if you're careful, they are just there for "anti-reverse connection".

Anti-reverse connection: 1. The input terminal is connected in series with a large current diode, such as 10A10

[tekguy]

this is the add with my pcb .

[tekguy]

so when you say black wire to A- quote,is it the thick black or thin meter ground?,quote:For one of those volt/amp panel meters with a thick red and black pair and a thin yellow wire, you should connect:

- black to A-
- red to A+
- yellow to V+
also i assume the yellow should go to the in+ve to measure the load voltage,i thought there was issues with these meters having a common ground or something?.

[ledtester]

- black to A-
- red to A+
- yellow to V+

Yes, I'm referring to the thick red and black wires here.

The thin red and black wires go to some power source. For instance you could use the 12V supply.

also i assume the yellow should go to the in+ve to measure the load voltage,

I'm not sure what you mean by "in+ve", but as I said above the yellow wire should go to V+ which is the same as IN+ -- check the traces on the PCB.

Of course, I'm making an assumption of what panel meter you have.

i thought there was issues with these meters having a common ground or something?.

What exact model meter do you have?

[tekguy]

the yellow wire is the voltage sense wire for the meter,its the thin red and black feeds the power for the voltmeter,surley the yellow goes to the third pad up on the left of the pic marked v+?.

[ledtester]

In my first reply I said:

...
- yellow to V+
...

[tekguy]

well i got this going,the most load i could wind it upto was 3.9amps with a 15v input from my psy,it was going for maybe 3 mins then bang a 1000uf cap exploded,no venting just blew the can clean off,its the 1000uf nearest the main input connections for the ampmeter+voltmeter etc,just measured my psu for ripple and its 6.3mv,any idea what caused this?.

[ledtester]

Probably this:

What happens when you put an electrolytic capacitor the wrong way?

https://www.eevblog.com/forum/beginners/what-happens-when-you-put-an-electrolytic-capacitor-the-wrong-way/

[tekguy]

Forgot to mention,ive fitted all the electrolytics on the pcb with the -ve corrisponding to the white marking on the pcb,is that correct on these chineese boards?.cheers.

[tekguy]

Well looking at the pics i have the caps polarity correct,acording to the pics on the sellers website and pcb markings,the pcb was powered by a 12v wallwart and the load input my linear psu outputting 15v ish,the cap that blew up was a 16v 1000uf item,is the voltage rating to low?,otherwise i cant think what caused it??.cheers.,should this now be in the repair section?.

[ledtester]

Was it C7 that blew up?

If you're feeding in 12V DC into the "AC 12V Input" then you probably don't need C7. In fact, if you're feeding in 12V DC you can bypass the rectifier bridge completely.

If you used the cap supplied with the kit then it is very possible it was defective or mismarked to begin with -- these kits are put together using the lowest cost components. Try with a cap from a reputable distributer.

[tekguy]

well i replaced the remains of the cap with a nichicon 1000uf@50v,it now does 4.5a max with a 15v input,i notice only 2 of the 0.22 ceramic resistors are getting warm,the other 2 are stone cold!.also the chineese amp/vold meter is well off even after adjusting the trimmer pots,by about 15%.

[tekguy]

yes it was c7.

[tekguy]

i assume it not reaching full power as sutch and only 2 power resistors getting warm i have a pair of dead fets?,I have just scoped the gates and they all look the same,any idea where to go on this,max load it manages is just over 5a max at 15v.

[ledtester]

Modifications and MOSFET selection for this design is discussed in this thread:

https://www.eevblog.com/forum/projects/upgraded-lm324-based-150w-72v-10a-electronic-load/msg1506610/#msg1506610

also the chineese amp/vold meter is well off even after adjusting the trimmer pots,by about 15%.

That's about par for those cheap meters.

[tekguy]

would mxp1005at FETS WORK IN THIS?,ITS JUST I HAVE SOME TO HAND,CHEERS.