Re: [DML] Run Cooling Fans Flat Out ? / Bob Zilla

[Martin Gutkowski <webmaster@xxxx>]

Hi Bob

**waves frantically** it's the irritating english guy from Memphis :-)

'fraid I've got to question some of what you've said here, mate...

ZillaDelorean@xxxx wrote:

> Here's the rub:
> If you choose to pass the current needed (20 Amps minimum ) through both the 
> stock relay sockets ( blue fan fail socket & fan relay socket ), you will be 
> running some of those terminals at their design current limits.
*cough* - The DIN relay standard for this type is 40A...

> That's 
> assuming the car was brand new, the terminals are very tight and completely 
> without oxidation ( tarnish ).
This should allow 40A without excessive heating. I agree it probably 
doesn't but we're not actually talking about a continuous 40A in this case.

> Well, the car is 20 years old. It is likely that connectors have been 
> jockeyed in and out of these sockets for many years. The more expanded and 
> tarnished they become the less current they can pass efficiently. As a 
> result, they are likely to overheat and melt down a relay socket.
Agreed.

> As if things aren't bad enough, running the fans continuously overtax the 
> Alternator. With the fans running, the Alternator is required to supply 20 
> Amps Min at all times. That's assuming nothing else in the car is running. 
> Very unlikely ! At night when cooling is needed the least, you are also 
> running the head lights ( another huge draw ). 
> What, you haven't had enough alternator problems already, you want to tax 
> it more ?
I'm puzzled as to why you think that drawing current from an alternator 
below its rated output will cause it problems? No, I'm being pedantic. I 
know what you're saying, but even with the FanZilla, the fans will still 
draw the same current. You're not giving the alternator a "rest" by 
turning the fans on and off all the time. In fact you'll probably give 
it more wear by loading it with the startup current repeatedly. This is 
opinion though. FWIW I still have the Ducey and deserve everything I get :-)

> The temptation to modify the stock relay wiring configuration is often 
> appealing in the short term. In the long view it's not the way to go. Should 
> you EVER decide to sell your car, the next owner will have no idea what 
> you've done. Many new owners can attest to this. 
100% agreement. I love my car for many reasons, but one of the main ones 
is it's complete lack of any kind of mods. (Except one - the dash lights 
come on with the headlights and not with ignition!). Even when I'm 
modding it, I will not permanently change the wiring.

> The Beauty and Magic of the "Duty Cycle".
> Every Engineer is familiar with this concept. It allows a device to work way 
> past it's design limits.This holds true for the DeLorean. By allowing the 
> cooling system to Cycle, it runs at nearly a 50% duty cycle. This means in a 
> typical AC cycle configuration, it passes current for only half the time, 
> allowing the entire electrical system to cool down. 
Okay, a "duty cycle" is the ratio given between "on" and "off" but only 
over a specific period; **typically a minute**. Of a motor, this is 
given by the S2/S3 rating. S2 defines the maximum length of time the 
motor can output nominal power before reaching maximum operating 
temperature. S3 defines the duty cycle the motor can handle if repeated 
ad infinitum. The same fact can be applied to actuators with supposedly 
small, weak motors....

I also want to question what happens when the cooling fans kick in at 
idle to cool the engine. On my car it takes a good minute to bring the 
engine's temp back down to the point of the otterstat cutting off. This 
is a far longer duty than the AC generates and easily long enough for 
any heat problems to become apparent.

> This is how the terminals 
> in the relay sockets can work past their design limit. The Lotus Engineers 
> knew EXACTLY what they were doing. If your cooling system is up to snuff it 
> will work just fine. 
I was under the impression that Lotus engineered the chassis. DMC wired 
the cars up using Lucas parts? I doubt very much that they "designed in" 
a time period to allow the wiring loom to cool down!!! THAT would be 
treating the symptoms and not the disease.

> When you decide to run the fans continuously to remedy a poorly functioning 
> cooling system you are treating the symptom and not the cause of the problem. 
> Do yourself a favor: 
> FIND THE REAL PROBLEM AND REPAIR IT PROPERLY.
...by cleaning/replacing the crimps, using new relays and for god's sake 
TEST it before taking a long trip! YES, I've done this to my car because 
of my low gas problem - that will be fixed, but meantime this takes a 
LOT of load OFF the electrics. Who knows maybe one day I'll get around 
to actually building one of my fan delay circuits :-) I think, however, 
running the fans continuously makes more sense though.

FWIW I drove over 400 miles over the weekend with my fans running 
continuously when the AC was on. Steve Strelczak has been running his 
fans continuously for weeks now while a new otterstat turns up. I will 
warn him to keep an eye on it.

My car has only 5000 miles on it and has very clean electrics... I am 
unlikely to suffer as others, so I bow to your superior experience with 
DeLoreans.... I just have to stick my bib in on specific electrical 
facts.... sorry.

Martin
#1458
(Degree in electronics and builder of fighting robots which use S2 
motors at 200A+ to the point of catching fire <grin>)