Brian said:
Ian, I am not motivated to get you to back-track or grovel or be in
any way uncomfortable. But auto makers found that auto interiors are
rather harsh for electronics. And the mechanism I mentioned is only
one of several. I guess that applies to boats too, just like it did
with motor-bikes (....obligatory sneer at Lucas omitted...)
Anyway - 100 V spikes are just everyday events for a vehicle with
switched motors, relays, and alternators. - would you believe?
If you don't want to choose a 1N4004 rather than a 1N4001 or
whatever,that's just fine with me. Are you aware of the price
difference?
Brian W
As you point out, the price difference is negligable. If you are buying
in quantity you may even get better price on the 1N4004 as it is commonly
used in small applience SMPSUs to form the bridge rectifier.
I think the common factor between cars and bikes is the use of the
chasis/body as the -ve return, while a competently installed boat 12V
system NEVER uses the hull as the return. This means that any spikes due
to load dump transients from the alternator, SHOULD be shunted by the low
impedance of the battery banks as the -ve from the engine block (or
ideally the isolated -ve from the altenator) shoult connect to the feed to
the -ve distribution busbar at the battery terminal so you dont see the
impedance of a grotty bit of verdigris encrusted copper braid (most land
vehicle -ve battery cables are in less than ideal condition) as a common
element in the charging and load circuits. Also marine battery banks are
usually higher capacity and better maintained, therefore of lower
impedance. Lastly, how often have you seen someone jump start a boat?
Considering this, I would expect a comparitive study of marine
intallations and land vehicles to show us an interesting difference in the
average amplitude of the transients. However, if the cost is not
excessive, in a safety critical system which would be disabled if the
diode shorted, assuming that the Auto industry data is applicable and
using the higher PIV raed1N4004 to 1N4007 and the 1N5404 to 1N5408 series
diodes is understandable and probably reccomendable.
Finally do you think the use if fast rectifier diodes like the UF4004 and
UF5404 would offer any significant benefit in reducing residual arcing and
spikes?
--
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk [at]=@, [dash]=- &
[dot]=.
*Warning* SPAM TRAP set in header, Use email address in sig. if you must.
'Stingo' Albacore #1554 - 15' Uffa Fox designed, All varnished hot moulded
wooden racing dinghy circa. 1961
