Window motor current draw

[BDA]

Does anybody have an idea for how much current window motors draw?

[Grumblebuns]

Is there any place where you can rent a clamp on ammeter I'd let you borrow mine except the postage both ways will probably be more than the ammeter.

[BDA]

I really appreciate the offer, Grumblebuns. The reason I was concerned is that I'm adding relays to my window motor circuits and the live wire to the relays will be fused. What I figured was that since US fuse ratings are roughly equivalent to 1/2 the British fuse rating and since the standard window motor circuit (as all standard circuits on the car) go through a British 35 amp fuse, I just figured a 15 amp fuse for the live wire to the relays was close enough. We'll see...

[314159td]

In general, fuses in these cars are there to protect the wires. The failure mode is too much current travelling thru the wire, generating more heat than can be safely dissipated, melting the insulation and potentially catching fire.

Match the original wire gauge, then match a fuse to that gauge's dissipative capacity or lower, never higher. If there are smaller gauge branches from that main supply, they need to have their own smaller fuses in the event one motor goes out or tries to draw all of the current. That changes with electronics, but you can apply broad rules to simple 12V stuff.

The ABYC rules on wiring are actually a decent (thought conservative) guide as boats today are still wired like cars from the 1960s.

[Kendo]

Doesn’t the rating difference between USA and British fuses have to do with one of them being fast-blow, and the other slow-blow? If so, is it better to have one or the other in a car?

[BDA]

You have it correct, Kendo. I've attached a document that describes it. I don't know which is better. I suspect it's a "tomato - tomato, potato - potato, let's call the whole thing off" sort of thing. If you think one way, you use US fuses or if you think the other, use Brit fuses. Just don't put a 35 amp US fuse where a Brit 35 amp fuse belongs.

[Grumblebuns]

What's scary is that the yellow power wires to the window motors are not-fused. They tap off upstream of the  fuse block. I don't remember what the wire size is, at least 14 gauge AWG or British equivalent, maybe 12? Anyway, on British Wiring's website "14 gauge" equivalent to 28 strand is rated for 17.5 amps and "12 gauge" equivalent to 44 strand wire is rated for 25.5 amps. I must have operated the windows on my TCS a couple of hundred times and I don't remember what the ammeter on the dash read while operating the window switches

[TurboFource]

So are the British fuses more or less than USA? What should I be using since I am currently going through dash wiring....

[BDA]

I just looked at the wiring diagram quickly and didn't notice that the yellow wires were before the fuse (that's just like me!)! Shouldn't those yellow wires be white (hot only with ignition on, unfused)? On the other had some standards list yellow for door locks (https://www.triumphexp.com/article/lucas-wiring-colour-guide.50) which I suppose has a certain equivalence.

[BDA]

So are the British fuses more or less than USA? What should I be using since I am currently going through dash wiring....

You should use roughly half the amperage of a US fuse that replaces a Brit fuse but you should use the Brit fuse in the first place. Of course when you add electronic gizmos, their manuals will use the US standard (unless you got the gizmo from England!). Check the document I attached earlier.

[Fotog]

Any information about the current requirements of any gizmo is independent of the source (US or UK).   A component that's said to draw 5 amps should nominally draw 5 amps whether it's been specified in the UK or US.  It's only how the fuses work and are rated between the different countries that differs. 

[BDA]

 

[EuropaTC]

Hi folks,

I'll start off by saying that I have no idea what the motors draw in normal use, only a vague memory from watching the ammeter and my recollection is that the big jump, 10 amps or more, came at the end of the window travel when it hits the stops and I was still holding the switch down. Normal travel didn't register so much, maybe 5 amps or thereabouts.

Having said that, when I fitted the relays to both the Europa and Elan window motors I just went for broke and fitted far higher capacity relays. IIRC they were 30amp units or maybe 40amp, I'm just not sure and don't have the invoice in either file. It won't help you guys over the pond but I bought everything from here, including another fuse box which is located in the front of the car;

https://www.12voltplanet.co.uk/make-break-relays.html

I ran brown wiring for the relay power feed to match in with the higher rated wiring from the ammeter. This is definitely a good mod to make, the speed of the windows is just like a modern car, even when the motor isn't running and you're just working off the battery voltage.

I've attached the modified wiring diagram for anyone interested. The original is higher quality but won't pass the 1024 limit on attachments.

Brian

[Fotog]

Nice documentation, Brian.  I hope to do that some day.  Thanks!

[Fotog]

Link to a short video showing my ammeter as window is raised and lowered:
https://photos.app.goo.gl/puWxHY7RYwGuhD1P7
It looks like it's roughly 15 amps, going to maybe 20 when the motor stalls. 
If you're not able to view that video, let me know and I'll figure out another way to post it.