Buyer beware may be LM338...... advice Welcome !

[Harry Dalek]

Not quite correct Harry, many parts are made in China that are just fine. Those under supervision of a reputable company, Fairchild, Microchip and many, many, others with a proper Quality Control program. Those in the video are an obvious out-and-out scam (The TO3 packaged ones). The guy with the TO220 devices I think it is simply not having a heatsink - also no small (100n) caps on the input or output quite possibly leading to instability....especially with an inductive load (motors).

Any case Steve i will add that advice to my shopping searches next time ! i tend to look at reply's as to what other people have said about the parts this one had nothing

Those LM338's you bought, you cannot see if there's actually a chip inside without an X-Ray machine. Or simply they're all just duds.

Caveat emptor - Buyer beware.

Yes i did think of smashing one open but i came to my senses and thought i would try a lower power supply on a few and see ....This time it worked fine on a few tried so there is a regulator init ...this pleases me at least so far its as good as a LM317 ....Next i will test it with a 24 volt supply from the phonoVision project see how they hold up ...i hope i just had a few duds in the batch if not these are not up to the LM338s standard ...i will Test tomorrow .

[Steve Anderson]

The absolute maximum difference between the input and output terminals is 40V, recommended is 35V maximum. Also re-reading the datasheet, a 100n disc-ceramic cap on the input and at least 10uF electrolytic on the output to keep the thing stable...and don't forget the heatsink! The metal tab is connected to the output pin, make sure the heatsink is isolated electrically from other stuff or use an insulating thingy.

Steve A.

[Klaas Robers]

Harry, I saw that the thing behaved properly until you dimmed the voltage. Then there was still running 0.5A.! I would suggest you to see what happens if you do the same test, but with no more than 0.1 A load, or even unloaded. It is possible that the temperature shut down doesn't work properly, or fast enough, but if you keep the dissipation low enough, that they will work. Then you still can use them as a stabiliser.

The effect that I saw is a transistor, that works properly, but with too high dissipation and too low heat sink. And then the transistor dies the death of heat. That is the collector and the emitter are welded together. Have you been holding your fingers to the stabiliser when you did this experiment?? Try it, but switch off immediately after you burnt them.

[Harry Dalek]

Harry, I saw that the thing behaved properly until you dimmed the voltage. Then there was still running 0.5A.! I would suggest you to see what happens if you do the same test, but with no more than 0.1 A load, or even unloaded. It is possible that the temperature shut down doesn't work properly, or fast enough, but if you keep the dissipation low enough, that they will work. Then you still can use them as a stabiliser.

The effect that I saw is a transistor, that works properly, but with too high dissipation and too low heat sink. And then the transistor dies the death of heat. That is the collector and the emitter are welded together. Have you been holding your fingers to the stabiliser when you did this experiment?? Try it, but switch off immediately after you burnt them.

Klaas that video is not me just some one else that had problems with hes Lm338s.

But i am using my supply for a dc motor control as well thing is i am having no problems with the Lm317's which i am using about 5 in parallel dissipate heat and they are handling this fine ...i don't like using these in parallel but it was a solution at the time for testing experimenting .

I was and will use your PDF on motor control to work on better speed control of my recorder in time that was my next step ..but i was not expecting the problems with the LM338T's just to supply the voltage to the improved idea ! i only needed 1 good one out of the 100 ! looks like this will not be the case as i can't trust them ...Testing on a lower supply voltage 12v that adjust the voltage fine so i think i am just going to use them for 12 volt to 5 v when needed i can see using them even at the range of what a LM317 is useless instant death of the regulator ! i will be chatting again to the seller ! i want them all replaced .

Reason i ordered the LM338Ts to just use one of these ...and replace all the LM317s

I did do some more tests today to see whats up and i will post up the results in the next post reply to Steve .

[Harry Dalek]

The absolute maximum difference between the input and output terminals is 40V, recommended is 35V maximum. Also re-reading the datasheet, a 100n disc-ceramic cap on the input and at least 10uF electrolytic on the output to keep the thing stable...and don't forget the heatsink! The metal tab is connected to the output pin, make sure the heatsink is isolated electrically from other stuff or use an insulating thingy.

Steve A.

I did make a mistake on the supply input its not 24 its 34 volts Still they should work to 40 volts input .

OK Steve here are the results hooked up just as you have mentioned the regulators that i know worked fine on the lower 12 volts supply die instantly in the 34 volt circuit which the Lm317's work fine in but replace them with the so called 5 Amp versions they die instantly no heating up time nothing just death !

Testing the Lm338 before used in a conductivity test with the multimeter ...meter ground on the output pin and on the adjust it shows 757 and 807 on the input pin ..... after a quick test in the circuit with the 34 volt supply the voltage does not adjust at all ...
Taking the regulators out after they have been used in the circuit 3 of them show same 757 on the adjust pin but the input pin shows 315 355 400 on the 3 dead regulators
On resistance test the input pin is 190 ohm 240 270 ohm when used and dead
So these regulators do not work with in data sheet specifications ..there's a regulator in them but its not a Lm338T ..and i will tell them alright .
I also experimented and hooked 2 or 3 together always the same result one at least fails instantly ! the other 2 or one seem fine but the failed one causes the others to not work logical may be 4 or 5 together but whats the point ...they will only work with low voltage amp supply not what it is or i payed for .

[Harry Dalek]

I gave it to them in a few replies ...
This is not on ! i am explaining you are selling fake LM338T regulators this would be against the law in China ? all i ask for is real LM338T regulators this is the last time i am asking for them to be replaced ...your next reply is your choice ! i want the real 100 LM338T i ordered ! please resend !

The reply from the seller below ! i will now wait and see what they resend !
Not only that they gave me a choice of what they look like ...i told them i don't care what they look like i care that they work !

ok.if you need ,we can resend a new package to you.

[Steve Anderson]

If you bought them through E-bay, Alibaba etc. is there no mechanism in place to protect you in these circumstances? Usually they have a customer satisfaction rating too.

Whatever, we'll await what turns up this time, though I'm not that optimistic.

Steve A.

[Harry Dalek]

If you bought them through E-bay, Alibaba etc. is there no mechanism in place to protect you in these circumstances? Usually they have a customer satisfaction rating too.

Whatever, we'll await what turns up this time, though I'm not that optimistic.

Steve A.

I have only used Alibaba a few times ,Ebay is similar to this the seller and buyer have a chat first if there's any problems ..Yes all 3 have satisfaction ratings and aliexpress also has postings as well so hard for them to not fix any thing like this or people might more on to another seller if they see a bad report .

It was just 16 bucks but i hope they send some real ones this time they look different to the type sent ...up to them really i made it plain what would happen if they did this again ! mad Harry ...i will post up what turns up .

[Andrew Davie]

AliExpress has ****extremely good**** customer support/satisfaction.
I find the "chat online" option and although it's hard to get past their "helpful robot eva" you can do that.
And when I have a person online to help me, I'm always polite, state exactly what happened. They then raise a dispute.
For me, all four of the diputes I've ever had have been settled in my favour.
When you get AliExpress involved, it's big bikkies for the sub-store involved. They don't want a bad rating because they can be kicked off the site.
That's the route I would go. Sellers will try and con you and/or delay you until various deadlines have passed.
With bad goods, I'd go directly to AliExpress themselves, and demand a refund - not a replacement.
The replacement - if it ever arrives - will be not what you want.

[Harry Dalek]

AliExpress has ****extremely good**** customer support/satisfaction.
I find the "chat online" option and although it's hard to get past their "helpful robot eva" you can do that.
And when I have a person online to help me, I'm always polite, state exactly what happened. They then raise a dispute.
For me, all four of the diputes I've ever had have been settled in my favour.
When you get AliExpress involved, it's big bikkies for the sub-store involved. They don't want a bad rating because they can be kicked off the site.
That's the route I would go. Sellers will try and con you and/or delay you until various deadlines have passed.
With bad goods, I'd go directly to AliExpress themselves, and demand a refund - not a replacement.
The replacement - if it ever arrives - will be not what you want.

Well i really want to give the sellers a bad report just for what they did , and i am willing to wait a few weeks all they have to do is replace the bad regulators with good and get out of it .....16 bucks means nothing really i am not to bothered ...reason i did not ask for a refund ,i want them to work now and give me what i ordered if not i will go down your road mentioned and make them feel like they are in a Quentin Tarantino movie ...without the blood and guts of cause

[fertooos]

Mine was on a heat sink but no indication of ever working no heating up at all no need to dissipate the heat output same as input voltage ...hes might of just been genuine then as you think .

Moderator note: apologies for the considerable delay in approving this post. I slipped under the radar, not noticed by the moderators.