Electronics > Beginners
Diodes in parallel.
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Gregg:
If the batteries are the same chemistry why not just parallel them but fuse each battery with a fuse slightly larger than the load so that if one battery happens to fail short circuit, the fuse will just blow.  I do this with my shop alarm batteries after trying diode isolation and finding out I was just wasting energy and complicating things.  I put a small LED with a resistor across each fuse to give a quick visual if a fuse has blown.  To change batteries or isolate one for testing, just pull the fuse.
Rick Law:

--- Quote from: wraper on July 18, 2018, 01:36:35 am ---
--- Quote from: Rick Law on July 18, 2018, 01:27:28 am ---So from my understanding of your reply, it would appear that I am okay as long as if my total current is not exceeding the rating for each individual diode.

--- End quote ---
But then there is no point doing this. Imbalance would depend on how different diodes are, so it's a pure luck in picking diodes and each device built will be different. Also important how good is thermal coupling between diodes and if some diodes are not headed by something else. It's okayish when they are in single package as they are thermally coupled and likely closely matched. But when you start placing separate diodes on the PCB, it get's really bad. Even trace length and width to each diode starts matter a lot. It could be 20mV voltage drop on the track which causes 3 times different the current through parallel diodes.

--- End quote ---

Got it - I understand that one.

My experiment happened to use the diodes from the same roll.  So that part is okay.  I should put some thought into how to get a shared heat sink or other ways to couple them thermo-wise.

Well, may be the experiment doesn't need them (< 1amp), but for sure if/when I do one for higher current.



--- Quote from: Gregg on July 18, 2018, 01:45:52 am ---If the batteries are the same chemistry why not just parallel them. ... ...

--- End quote ---
Experimental only.  So I am using batteries that I redeploy on something else regularly.
wraper:

--- Quote from: Rick Law on July 18, 2018, 01:58:52 am ---My experiment happened to use the diodes from the same roll.  So that part is okay.

--- End quote ---
Even when they are from the same batch, usually difference is huge.
Zero999:

--- Quote from: wraper on July 18, 2018, 01:36:35 am ---
--- Quote from: Rick Law on July 18, 2018, 01:27:28 am ---So from my understanding of your reply, it would appear that I am okay as long as if my total current is not exceeding the rating for each individual diode.

--- End quote ---
But then there is no point doing this.
--- End quote ---
Lower volt drop.

I can see what you're saying, but in practise it does work. The current sharing isn't perfect, but it's enough to give a lower voltage drop, than what one would expect using a single diode.
wraper:

--- Quote from: Hero999 on July 18, 2018, 10:24:38 am ---
--- Quote from: wraper on July 18, 2018, 01:36:35 am ---
--- Quote from: Rick Law on July 18, 2018, 01:27:28 am ---So from my understanding of your reply, it would appear that I am okay as long as if my total current is not exceeding the rating for each individual diode.

--- End quote ---
But then there is no point doing this.
--- End quote ---
Lower volt drop.

I can see what you're saying, but in practise it does work. The current sharing isn't perfect, but it's enough to give a lower voltage drop, than what one would expect using a single diode.

--- End quote ---
It's pretty crappy way to decrease the voltage drop to begin with. As BrianHG suggested, if you want low voltage drop, use MOSFETS.
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