Ammeter fitting

Post by **lowedb** » Fri Sep 12, 2003 8:17 am

I have to disagree with the point about 'radiation' from the cable running in the cab. Any radio frequency noise (interference) generated by dynamos, motors, relays etc will be on all cables. The harness acts like an antenna. The high current wiring is carrying more DC, but that produces a static magnetic field, no electromagnetic radiation. Manufacturuers are not running cables away from passengers for fear of litigation. What they are doing is reducing the emissions from the motors, ECUs and so on so that they don't interfere with the rest of the world, and on board radios, phones, TVs etc. They have to do this because it's law as well. Don't even get me started about the junk talked about mobile phones and 'radiation'

The point about the fire risk is well made, but can be overcome by adequate fusing. Of course if the fuse fails, you lose everything.

I don't understand the point about not using the body as the earth return. That's exactly what you do do. All ground leads are kept as short as possible.

I have to disagree about safety, too. properly modern cars (last ten years) may look worse after a crash, because they have absorbed all the impact. I'm not a fan of airbags, but crumple zones, side intrusion beams, anti burst locks, collapsible steering wheels, pretensioned seatbelts, ABS and so on DO make cars safer, and the mog has none of these. It does have character, and is fantastically easy to maintain, but I wouldn't want to crash in one, ever!

Post by **Chris Morley** » Fri Sep 12, 2003 8:08 pm

Scott, it was 3 a.m - I'm something of a midnight owl and I had a lot of stuff to go through after getting in from the pub.

Cats are also called moggies here - in fact my two moggies often sleep inside my (rusty) mog !

I'm using the work computer now (tsk tsk...

) and I still can't see the images. Sorry to say I didn't see any Minors in Sydney when I visited a few years ago and I kept my eyes peeled.

You can't deny the advances in car safety and Lowedb is right to highlight the improvements and point out that crumple zones will look awful after a crash. Not that many small cars have all of these features even today.

The Minor's 'safety cell' however is probably superior in certain respects to many modern cars and that saves lives in certain circumstances. My main worry with the Minor is that the seatbelts are inadequate. I can't say I want to have a crash in any car, even if it is modern.

Post by **Gareth** » Fri Sep 12, 2003 8:12 pm

I can't see the images, either.

Make sure that when you wrote your signature, you set it out like this:

Code: Select all

[img]http://www.mysite.com/mypicture.gif[/img]

Don't put any spaces after the [ img ] command.

Post by **washer-bottle** » Sat Sep 13, 2003 12:59 am

lowedb is correct, but I got you all talking. I am not saying they are right - just that its being looked at! Yes EMC is important and as for mobile radiation I couldn't possibly comment - wait 10 years. Some even worry about the field generated by the wires in your car tyres when rotating.

What I wanted to say was that what is unique to fitting an ammeter is the high DC current inside the cab still gives of some radiation due to the ripple from the alternator as its on the direct feed from it to the battery.

The idea of the seperate return on a rear battery is to avoid going through the chassis with the high starter motor current. Some people even talk about twisting the cables - sounds like nonsense to me.

As for safety fit extra fuses to your Minor then only part of your electrics "will" fail. For winter wiring tips from the Prince of Darkness see
http://www.kitcar.com/articles-kitcar/h ... rince.html

I am not starting on about safety of modern cars - you are right they just make you feel safer. Just remember that the steering column is like a javelin pointing at your chest and there is no crumple zone to take any impact when you are behind the wheel of a Minor. Thats why Minor drivers are generally safe drivers.

"He who drives like hell gets there first".

Fit your ammeter, marvel at the power and have a good weekend.

Post by **dennis** » Sat Sep 13, 2003 12:29 pm

well that has put our minds at rest about the steering acting like a javelin, i am pleased you mentioned that point!!!!!

Post by **lowedb** » Sat Sep 13, 2003 1:30 pm

Field generated by the car tyres rotating? How does that one work? Earths magnetic field? Anyway the rotation of them is such they wouldn't move a loop through the flux, as they rotate in the same direction as the wires run.

Yes there is some ripple from the dynamo / alternator. But this is pretty low frequency. The effects of the mains wiring in your house would be far worse.

I don't see the advantage of not using the car body to carry the starter current. So long as its properly welded together, and the connections are sound, then where's the benefit in a separate lead?

Twisting wires together is good for stopping them picking up interference. The electromagnetic field counteracts itself in each twist as the wires sit the opposite way. The voltage induced in the first loop, opposes that in the second. Great for audio sstems and sensors on engine management systems, but not much effect on a bulb.

Post by **rayofleamington** » Sat Sep 13, 2003 8:38 pm

using the body as the earth is fine, but with a rear mounted battery there is more variation in the local voltage at each part of the car during cranking. If something starts to malfunction then this extra difference in earth potential and earth spikes can cause problems on modern electronic systems. So the fall back solution is anadditional front to rear cable to carry the starter current, but that would be a rare choice.

crumple zones and vehicle crash design is high priority to manufacturers and can be a leading priority (there are well known examples where crash safety improvements are allowed mid development when other improvements would not be considered)
Head on crashes, and offset front crashes used to be high on the fatality list so it's good that modern cars are constantly improving.
The front of a moggy has a crumple zone, although I'm not sure if it is intentional. If you see a minor after a light or medium front on accident the front end has crumpled, with the bumper passing force to the inner wing, which bends and rips away from the engine bay floor.
I don't know how it would do compared to a 10 year old car, but for its time it is very good.
If you use a minor without a seatbelt, then you should talk to a retired ambulance driver!!! They were well known in the 60's as following head on accidients the driver was usually found dead with the steering column through his chest (the steering wheel would just break away)

As for EMC from using an ammeter - I thought the comment was a bit tonge in cheek, as compare to using a mobile, or living near pylons it would not register on the scale. I woud still be nervous about running the entire current through the dash on 1 wire - if anything fails and draws high current you'll have a smoking wire unless it is properly fused.

Vehicle wiring looms are also being changed to reduce weight, and cars now come with communication networks, so the rear lights or wiper will be activated by a signal betweeen modules. not hard wired from the switch. Less wiring = less weight. (not a problem on Minors as the loom usually weigh less than the waxoil)

Post by **lowedb** » Sat Sep 13, 2003 9:58 pm

Mmmm.
Sounds like Ray of Leamington might have experience of modern vehcile electrical systems. Dead right about the way systems operate today with complex networks. (Ray, if I say CAN do you twitch?)

There is a difference during cranking, but the systems are well able to cope. During normal running, though, I'd still stick with using the body. The cars I work on have two batteries, both in the boot (there's no room under the bonnet) and we are quite happy that the body is the best earth return.

Remember we are talking about Moggies though! I maintain that the comments on EMC and earthing / routing of main current cables that were made regarding how it can affect people are open to question.

I've unintentinally moved the debate onto modern cars, and that's not the point. The great thing about Mogs is being able to fit the entire wiring diagram onto the back of a postage stamp. There isn't a single thing that you can't figure out with just a bulb on the end of a wire.

Post by **rayofleamington** » Sat Sep 13, 2003 10:14 pm

Oh the wonders of high speed CAN! Fortunately that's only a side issue for me. A couple of wires that make the car work - in theory...

There isn't a single thing that you can't figure out with just a bulb on the end of a wire.

Modern cars... are one of the reasons I like minors.

Post by **Kevin** » Sun Sep 14, 2003 12:22 am

Now that I am totally lost with the technical expertise show above how do you suggest is the safest way and how should an Ammeter be wired and with what guage cable and fuse etc, that is bearing in mind we are talking Morris Minors and not the latest Vovlo type `R` a friend has just turned up in.

Post by **rayofleamington** » Sun Sep 14, 2003 11:04 am

the fuse should be rated large enough to take the maximum current that will pass through.
>>Hopefully someone has some experience on that, and can suggest an appropriate value?? <<
To be accurate, add up all the currents of all the consumers (not an easy task). To do it the easy way I would just consider that there wasn't a fuse there to start with so even if you pick a big one it shouldn't reduce the safety.
The wire needs to be rated to take a current larger than the fuse, otherwise it can catch fire before the fuse blows. Safety would suggest a ratio of 2:1 . That is stightly overkill but would help you sleep soundly.

Also you need to consider the ammeter itself - does it have a maximum current or recommended fuse rating? Even if you protect your new wiring with the fuse, you may overheat the ammeter (during a short circuit fault) if this is not considered.

Sorry if this sounds a bit cautious, but there's a bit of saftey involved. I would be more likely to guess values on my own car, but am reluctant to guess for someone elses car.

(ps - sorry about going off in tangents. As soon as someone mentions modern cars, we tend to get carried away doing comparisons.)