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Old 18-06-2012, 16:53   #16
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Most modern alternators have " load dump " protection for circuitry built in these days. While this is to protect against just the battery being disconnected ( and not the load as well) in reality it also protects in a complete disconnect.


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Old 18-06-2012, 18:13   #17

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Re: Simple Question on Charging

Stu, I remember looking up the part number that was oin the original zapstop, and it was either a zener or a slightly more exotic diode, IIRC about $5 in single quantity from DigiKey around 1990, versus $25 for the ZapStop at West Marine.

And, it was made by some small company. Apparently later aquired by Xantrex, and since acquired by Balmar, who now integrate a FUSE in the package as well.

But diodes are still not one-shot devices. If you put enough power on them long enough to slag 'em down or blow 'em up, yes. But if you only want them to pass surges to ground, and you've properly specified the power rating?

Come on now, tell me you've EVER heard of a diode that blew, every time, in routine service. Tell me Zener diodes aren't used to send spikes to ground repeatedly.

Yes, I know all spike protection devices eventually die a heroic death. But that can mean hundreds of spikes down the line. The ZapStop as originally sold was only supposed to protect against the occassional "Oh sh.t! I switched the batteries and the engine is still running!" and it most definately didn't have to be replaced every time.

I expect Balmar's addition of a fuse, is to protect the line in case the diode fails shorted instead of blowing up.

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Old 18-06-2012, 22:41   #18
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Re: Simple Question on Charging

Try reply #10, here: Alternator Question? -
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Old 19-06-2012, 06:49   #19

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Re: Simple Question on Charging

Interesting to note that Maine is sayingthe Balmar's will blow their 10A fuse--instead of the diode. Which I think just confirms that the diode is not a one-shot device. The question is, rather, if a zapstop has been chosen with enough capacity to survive repeated use. There are 1-watt diodes, and 100-watt diodes, and more available out there. The ones that can survive higher power are usually "stud" designs, that (as you know) look like stubby little bolts, threaded to install in heat sinks. With the standard 500% marine retail market, those ain't gonna show up at the chandlery.<G>

I can also tell you why some automotive alternators have integral protection (against spikes and open outputs) and others don't. Money. As usual. If you put protection internal to the alternator, even simple spike protection, those components take hits and eventually fail. Delco had at least one model with internal spike protection and got panned because they were seeing large numbers of failures before the 100,000 mile mark, unacceptable for a car. Originally they though this would be a good idea because spikes can destroy those (at that time) thousand dollar LED tail light arrays, etc. and save a lot of other repairs. Except, it is hard to convince an owner that you've prevented other problems they can't see. Goodbye, integral protection.

Alternators have also been built to survive "no output lead" conditions because it is also quite common for the output lead to become disconnected by accident (while work is being done) or age (chafe & loosening) AND one of the oldest cons in the business has been for electrical shops and highway robbers to intentionally disconnect the output lead for 20-30 seconds and then say "See, this is why your battery is dead, your alternator was no good" intentionally blowing an alternator to make more work while replacing a battery.
There are a lot of (as you know) "heroic" regulators in the IC electronics industry, some of them have worked into alternator design. And if they cost 50c more...they won't be in anything "built to a price", so we can never assume they are.

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