Parallel Volt Regs And Ballast Resistors

Hello Michael,

Can't comment on the importance of that resistor, but fractional ohm resistors like that are available commercially if you want to avoid the space of a home-made resistor.

Do a Google search on "current sensing resistor .015 ohm" and also try Ebay. I've seen them there from time to time fairly cheap. Obviously, not all current sensing resistors are fractional ohm values.

Good luck.

Chuck

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Thanks Chuck, I looked at sites like Newark and they didn't turn up anything so figured they didn't exist.

Cheers,

Michael

Go to

But you might not need to spend any money at all if you just want some ballast resistance. Try using paper clips. The cheap steel in paper clips has much higher resistance than copper does, so you can use short pieces. Dab the end of the paper clip in some flux to make it easier to solder (electronics flux, not plumber's flux).

About the only difference between cheapo steel versus current sense resistors is that the steel has a big temperature coefficient, but that's actually a good thing for current-limiting.

Another thing you could try is get a hold of some nichrome wire, perhaps by cannabalizing a power resistor, but nichrome doesn't solder well.

Great idea!

Michael, if your ohmmeter doesn't let you measure down to 15 milliohms, you can pass a current of, say 1 amp, through a piece of clip and using a DMM, measure the voltage drop. Most DMMs ought to read 15 millivolts OK. This is a four-wire resistance measurement FWIW.

Chuck

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"Michael"

Post the link.

....... Phil

If you are going to try putting regulators in parallel, the resistors are generally necessary. Each regulator will be trying to control its output and doesn't expect other regulators to be doing the same thing to the same output, where some conflict can arise. The better value of the resistors will depend on the load and the regulators themselves, but the resistors provide a little bit of "working room" for each of the regulators to have some measure of control over their own outputs, as they were designed to have, while allowing their aggregate current handling to be summed into the load. Just wiring their outputs together isn't wise.

What kind of current are you talking about, load-wise? What's the regulator? (And are they just trying to sell you regulators, when a bypass transistor around it might do a similar job for you?)

Jon

I don't know what the OP was using, but here's one link to a datasheet that recommends the use of 0.015 ohm ballast resistors:

javascript:openreq('http://www.ortodoxism.ro/datasheets2/0/00hl8utol4qogo8hlqilf35r0opy.pdf') LT1083-FIXED datasheet

Bottom of page 9.

Chuck

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I've never had a problem soldering zinc plated paperclips using only electronics solder. I use pieces of them them between D connectors to make custom adaptors

or a toaster etc...

also 0.015 ohms would be a very short piece.