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Min voltage drop in silicon rectifier?

I want to isolate flooded lead acid batteries from each other using power rectifiers like these:

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I would charge them through the rectifiers.

From the graps, it appears that there is a 0.5V drop across the rectifier even at low current.

Inasmuch as the batteries could be ruined (boiled off) over time by a significant trickle charge, I need to know the voltage drop at, say,

10mA -- so I know where to set the float voltage.

How can this be ascertained, short of experimentation?

Ken (to reply via email remove "zz" from address)

Reply to
Ken
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The experiment is probably worth doing, because at 10 mA, the rectifier is operating way below the bottom of the graph. It shows that a room temperature diode drops about .65 volts with 10 amperes going through it. As the current falls, the voltage keeps falling at about 60 millivolts for each time you divide the current by 10 (for an ideal diode). So to get from 10 amps (the bottom of the forward voltage graph) to 10 mA, you have to divide by 10, 3 times, so the forward voltage will be somewhere around .65-.06-.06-.06=0.47 volts.

Reply to
John Popelish

Which sounds garbage to me. The drop will remain fairly constant.

That said: I think what the OP needs to do, is have some feedback directly from the batteries being charged, and use that feedback to control the charging voltage. The drop across the diode becomes irrelevant.

Reply to
John Smith

Why? I thought this effect is expressed by Ebers-Moll, or so. At

20C, 58.26mV/decade from (kT/q)*ln(10/1). But I'm a hobbist, so I'll listen to why it's garbage with rapt attention.

Jon

Reply to
Jonathan Kirwan

Ahhh, I'd say that going from 0.65 to 0.47 over a 3 decade range of current is "fairly constant"!

Best regards,

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

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Home of DaqGen, the FREEWARE signal generator

Reply to
Bob Masta

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