Bob,
When a tamping diode is part of the relay, which should be the positive for
the trip? 85 or 86?
Thanks for the overall explanation. I leaded something today :-)
TonyC
-----Original Message-----
From: Bob Tom <tigers@bserv.com>
To: dakota-truck@dakota-truck.net <dakota-truck@dakota-truck.net>
Date: Tuesday, September 07, 2004 8:24 PM
Subject: Re: DML: Interesting relay failure
>
>At 10:44 AM 9/3/04, you wrote:
>> Yeah, this wasn't a "standard" relay like what most people would think
>>of, it had a slightly different form factor, but it operated the same as
>>a standard 4 terminal relay. Actually, there is a 5 terminal version
>>of the standard 4 terminal relay, its got an extra terminal, usually right
>>in the middle. A "standard" 4 terminal relay has the 2 terminals for the
>>coil (12v switched source and ground) 85 and 86, then the 2 terminals for
>>the switched circuit (12v source - 30) and the output to accessory (87).
>>The 5 pin relay ads the 87a terminal, which is connected to the
>>12v source (30) when the coil is *not* energized. (In the proper
>>electrical terminology, its a "normally closed" switch as opposed to a
>>"normally open" switch. 5 terminal relays with both 87 and 87a pins
>>are both normally open and normally closed relays, they can be used for
>>either one, or both at the same time (almost like 2 relays in one) :-)
>> -Jon-
>
>The 5-pin relay is commonly called a Bosch relay but is made by other
>manufacturers (Siemens, Potter& Brumfield, etc.). They are the most
>widely used, versatile and can handle up to 30 amps, which is more than
>suitable for most applications.
>
>The 30 pin is set perpendicular to the other pins. Normally, it doesn't
>matter which way you pass the current on the 85 and 86 coil pins because
>if you hook it up backwards, the coil will still activate the relay.
>
>However, relays sometimes have an odd tendency to turn themselves back
>on briefly. To counter this, a diode ( a 1-way switch) is placed between
>85 and 86. This is referred to as a tamping diode. A diode wall has a
very
>high resistance in the opposite direction. When a tamping diode is used,
>it is important that the coil is hooked up according to polarity. If a
tamping
>diode is used and it's hooked up backwards, the result is essentially like
>shorting a wire out, which will likely burn something up eventually :-(
>
>I'm just wondering if what you were experiencing was this odd tendency.
>DMLers do seem to have odd tendencies :-P
>
>Bob
>
>
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