Back to the Morris. I have an ammeter, 30-0-30, and the dynamo is rated
13.5v, 22 amps. Still +ve earth. What I don't have is suitable brown cable, and there seems to be a lot of conflicting advice.Found cable described as 3.0mm? 44/0.30 27.5 Amp, which seems OK, or should I go for 4.5mm? 65/0.30 35 Amp to be on the safe side?
Any idea of 'standard' car Lucar connector size? Options seem to be
6.3mm, 8mm etc. I'm guessing 6.3, being equivalent to the old 1/4 inch?Thanks!
was the original brown?
Voltage drop is likely to be the no 1 consideration. 1mm2 pair drops 44mV p er amp per metre, so 22A 3mm2 drops 0.323 volts per metre. 1m of that is go ing to seriously hamper your battery charging.
you're the one with the measurand!
NT
Someone better informed will be along in a minute, but bear in mind that you don't want to introduce too much voltage drop in the cable and connectors on those ancient Lucas systems. My recollection (which may well be flawed) is that the original cables in those days were more like modern 6 mm^2 than 4 mm^2.
There isn't an original as such, but yes, the cable being extended is brown, so I would like to follow the same scheme.
OK, good point. I will go for the larger size. It is certainly a common addition to a Minor, even (or particularly) those still using a dynamo.
Well, yes, but measuring to a fraction of a mm with a steel rule is not easy, particularly when the connection is buried under the bonnet. I'm sure 1/4 inch was the 'standard' automotive size back in the day, and 6.3mm is close enough to 1/4 inch.
The terminals on a Lucas ammeter I have here are 3/8". I suggest you use
6mm cable as a minimum. Have you considered fitting a digital ammeter? The shunt resistor can be fitted in a plastic box somewhere where the battery lead doesn't need to be extended. Then you simply take two (thin) wires to the actual meter, or to the dividing circuit if the meter needs one. If it does, build the dividing circuit into a sealed box because otherwise damp affects it (very high value resistors are involved) and alters the reading. The meter also needs a supply and a ground. You can take the supply from the ignition circuit. If you get an illuminated one it's best to select one rated at 15V, otherwise the little LEDs will burn out prematurely.Bill
4.5mm2 will get you 0.215v drop at full current, not as bad but still hampe rs charging on an already low voltage output.
A battery voltmeter is a way to avoid the issue, preferably expanded scale from 10v to 15v, or in your case 14v.
NT
Many years ago I decided to add an ammeter to my Mini. No idea what cable I used but I sited the ammeter on the little shelf to the right of the steering wheel.
One day going to work I smelled burning and realised it was the ammeter and in a flash I grabbed the cable with my hand and pulled it with sufficient force to break the connections but not after the burning hot plastic and wire had seared my hand.
Of course nowadays I would ask on here before making such an installation. Drove the rest of the way with my right hand out of the sliding window in an attempt to keep it cool.
It's very easy to 'oversize' the cable to try and reduce losses but it could inadvertently mechanically overstress the connections either at the regulator, or at the ammeter
The 3mm^2 especially being multistranded looks similar to what would have been fitted new on cars thus equipped.
At these current levels sizing the cable to the connectors you will be using and getting a quality interface, preferably crimped, between the wire and the connector is IMHO slightly more important than the actual wire size itself.
The Lucar connectors came in iirc about 5 sizes, 1/4" being most common but also
3/8" 3/16" , 110 thou which is just below 1/8" plus half inch.The dynamo regulator connections will almost certainly be a mix of 1/4" and 3/8" and possibly 3/16" or on earlier models bare wires into screw terminal blocks.
Every wire will be brown, either plain or with a tracer. The correct colour codings are online.
Go for some kind non-invasive DC hall effect sensor, and log the readings digitally?
Use what Lucas did?
The metric sizes are simply modern measurements of the old. They are interchangeable.
You can actually just measure the voltage drop across the ground lead from battery to chassis. No need for a shunt resistor as such.
I made one for the ol' Rover which doesn't have an ammeter. But arranged it to drive a tri-colour LED. Red for discharge, amber for balanced, green for charging. A lot easier to fit on the dash than a meter.
Is this one of those plus and minus gauges? I used to have a Morgan on in my shed and it really was an ammeter, may of the ones you see these days have a shunt and a millivoltmeter sender and a normal meter or lcd. Brian
In message , "Dave Plowman (News)" writes
I fitted several ammeters to cars many years ago, but each came as a kit, with cable. Trouble is, I now don't know what Lucas supplied, back then. I find it very difficult to visualise what cable looks like. Easy to read the description, but without seeing drums of the stuff, I'm not confident I would choose the correct size from description alone.
Snag is modern cable can look very different from older stuff at a glance. From the pretty old woven fabric to the later PVC and later still thin wall PVC. But you can measure the diameter of the conductor and calculate the metric cross sectional area, which modern cables are specified in.
It also depends on what is wired via your ammeter. It will obviously show charge, but not everything on the car might be wired through it to show discharge.
However, as with all such cables, you won't do any harm using a larger one
- provided it can fit the terminals.
In message , "Dave Plowman (News)" writes
The main connection from the battery goes to the starter switch. From there (same side of the switch), a brown wire goes to the A terminal of the Control Box. The idea is to break that brown wire for the ammeter, so the ammeter reads everything except the starter motor.
The existing brown wire is probably 6 inches long, but mounted on the bulkhead, so extending to an ammeter would require an additional 18 inches or so, in both directions.
In message , The Other Mike writes
Very helpful comments and great links Mike. Thank you.
Dunno. Remember on my '55 MG Magnette, not everything was wired via the ammeter. The factory spotlights for one. All too easy to exceed 30 amps.
Must admit I'd be more inclined to fit an alternator so you don't have to worry about how many amps you're using. ;-)
And if you want to know battery state, a voltmeter is more useful.
Fit a 3" length of the biggest possible cable the connector will take into the connector. Connect this to a fatter cable by means of a soldered joint wrapped with self-amalg.
Bill
That makes the ammeter pointless.
Bill
In message , Tim+ writes
Well, possibly, but I have owned the car since 1996, and the dynamo has always been fine. I don't feel I need an ammeter as such, I just found it in a box of stuff in the shed. No idea where I got it. Found a +ve earth radio too, so may have a go at that.
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