dshepp806

Bird,..we've hit on this before and I liked your idea of DME protection at the relay rail. Well,..NOW, we've heard Loren state (essentially) the same.....I think I'm on to looking at an approach to protect the DME from overvoltage from an "outboard" approach. Geeze, guys will go the distance to keep the headlamp current off of the stalk contacts through relay modification. NOW, we're talking about protecting a much more expensive part such as a DME, from overvoltage......a no brainer, if you ask me. Yes, another failure point but so goes it.

I'd like to see these protection relays that you're mentioning Bird.

Best,

Doyle

dshepp806

I'd definately consider this an upgrade,..an important one, at that. Seemingly simple, at that (too).

Best,

Doyle

rusnak

^ Me too!! I'd buy one, but I don't consider myself capable of making one.

And was I being inconsiderate? I know how much Loren HATES Pelican Parts and Radio Shack both.

Lorenfb

"Loren, you have a Benz overvolt relay lying around?"

Yes, but it did its job, i.e. it's done. My customer assumed he had
a bad M/B ECM, but his charger 'cooked' the relay.

The M/B over-protection relay is a 'passive' device in that it blows
the fuse once over-voltage occurs. The ideal circuit would shut-down
the DME relay at a set voltage (16-18 volts) and restore the voltage
once the voltage was below the setting.

The circuit could be easily placed in the existing DME relay.

rusnak

I would love to buy two.

whalebird

Thanks Loren. That does clarify a bit. The rule was that if the fuse was blown, the relay was done. Some thought the fuse could be replaced. Try here, about 2/3 down the page, red top relay(aluminum casing). click on the image and you will see the pins, and their outputs. The circuits (85,30,15 etc) are the same for Porsche as benz. I would love to see a plug and play for such a device in a Porsche.
http://www.europartsdirect.com/epc-items.asp

Lorenfb

"The circuits (85,30,15 etc) are the same for Porsche as benz."

The problem is that the DME relay has a fuel pump control part
of it, i.e. part A - power to ECM, part B - power to fuel pump.

I'll come up with a circuit and try to fit it into a DME relay.

dshepp806

Well,..there you go! One helluva thanks to you, Loren.

Best,

Doyle

Lorenfb

Here's the circuitry added inside the stock 911 3.2 DME relay to protect the
DME ECM from an over-voltaging alternator:

rusnak

I move to make a new thread with ^ that diagram. Is there a second?

dshepp806

Nice,..very similar to::::::::

Thanks Loren.

I second that move, but would want Loren's blessing in doing so.

Doyle

rusnak

Absolutely. I was thinking a new thread with tags would make a better breadcrumb trail on Google for someone who was specifically looking to avoid a dme overvolt condition.

Lorenfb

"I move to make a new thread with ^ that diagram. Is there a second?"

Do it! It's for you guys to use to protect your electrical system.

"Nice,..very similar to:::::::"

That's correct, i.e. The BASIC functionality is the same, the defrost unit turns 'on'
a relay and the DME relay mod turns 'off' a relay. The defrost circuit is over-designed
by someone who had an interest in selling components to the defrost relay manufacturer,
Hella, and thus could have been simplified.

Remember:

1. The defrost unit - turns 'on' the center heat element with a cabin switch thru a relay
and the upper/lower elements are turned 'on' thru a second relay when the battery voltage
goes above a set point.
2. The DME relay mod - functions as a normal DME relay (powers the DME pins 18/35
and powers the fuel pump via the ECM pin 20) but then shuts-off if the battery voltage
exceeds 18 volts.

dshepp806

THANKS LOREN!!!!! I started a new thread, per your blessings....

Doyle

dshepp806

And thanks to Rusnak for the thread suggestion! Never thought my battery thread would end up with an overvoltage protect theme....I learned a lot on this one!!!

You are (and always have been) a big help to me Loren.

Best,

Doyle