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LEDs in parallel for demonstration purposes only is OK?

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treez

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A friend I know has been asked to do LEDs in parallel in 5W LED lamps for an automotive place. They use matched LEDs and parallel them, with no current limiting resistors in the paralleled strings. They are also *not* mounted on MCPCB.
The LEDs are in series strings of three LEDs...and these are paralleled.
The overall lamp is fed by a single current source.

He has been told to do it based on the fact that they say this is for a demonstrator car only.

Should he refuse to do it, on the basis that it will put them out of business?
 

CHEEZ....the things customers ask us to do. Then, when things fail...who is to blame?

I mean...how much more would it cost to add a SMALL amount of series resistance on each leg?

My personal opinion is:
1) I would make an attempt, in writing, to explain the technical reasons to do such and such. Be very specific, and use industry accepted data, not your opinions.
2) That would most likely trigger a response, also in writing. Regardless of the response, both e-mails go into your CYA folder.
3) Do as told by the customer, and if later s**t hits the fan, you have evidence.
 
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ake a lot of care, because even if the diodes are selected, changing the temperature on the chip will change the direct votage, in this case the voltage will be lower, then the current higher and so higher the temperature and so on up to the distruction of the diodes.

If you add a small balancing resistor, the situation will be better.

About the request, very often the customer is saying:
I pay and so I pretend.

In this case only wit a technical report that shows why it cannot work you can save yourself, overall if the situation will degenerate with the intervention of the lawyers.

Mandi
 
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I have "a friend" who has had to do all sorts of dodgy things to get a demo out of the door in time but that is because the time to do it properly isn't available. However, driving a few LEDs properly seems trivial and wouldn't fall in to that category.

Keith
 
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thanks, its the company that are asking him to do it (his employers), not the customer
 

My advice remains the same.

Let's say you heed your company's requests and then, at the worst possible time, something goes wrong...who do you think will get blamed? Your boss?
 

treez said:
Should he refuse to do it, on the basis that it will put them out of business?
Click to expand...
To start with, he should refuse to listen to anything further you have to say on the subject, otherwise his company will go out of business before you've made up your mind what to tell him.

Seriously, how long have you been going on about parallel-connected LEDs now? It seems like at least a year if not two, but maybe my sense of time has been distorted by the tedium.
 
There may not be much value in demonstrating something
that bears little resemblance to the final form. That depends
on what he's trying to demonstrate, what changes will ensue
between here and there, and whether any rational argument
that the hack-demo is indeed useful and sufficient can be
made.
 

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