Two ammeters in parallel

Maybe it is supposed to. Mine clearly didn't. The workshop manual describes the operation of the control box as a voltage regulator "incorporating constant voltage control for the charging circuit", with the contacts opening to prevent over-voltage being output. The implication is that if I am taking a lot of amps out of the dynamo, the voltage is unlikely to exceed the contact opening voltage and everything the dynamo produces goes down my jump leads.

I assumed it was a circuit board failure or a blown fuse that stopped them all working at the same time, but I have never looked at the way they work to see the possibilities. I have seen a diesel tractor started from cold using smouldering blotting paper as a glow plug, so it obviously doesn't need anything complicated in a car to provide heat, but it probably has associated computer linkage for the fault diagnostic system to report faults, and circuit boards do fail.

Elsewhere in this thread someone has suggested that perhaps the glow plugs failed progressively and when the last one failed the engine wouldn't start. That is a possible alternative.

I have no idea which is correct.

It was the dynamo not the starter motor. I typed the wrong thing. It was driving another car's starter motor (in parallel with my own battery) for a lot longer than would normally be the case, and the windings will have heated from the number of watts being generated. Dynamos don't have much of an integral fan for cooling.

Jim

Instead we get days of discussion in a group that mostly doesn't understand the basics of electronics, yet insists it does.

But you don't have to do it that way.

You can buy a 50A four point (kelvin connection) shunt, flip your multimeter to volts, and measure up to a

One of the panel meters for sale, is designed that way and includes an external shunt. But being Amazon, none of the units I reviewed have specs, and it's like buying a pig in a poke. You can't tell if it's 10% accurate or 1% accurate. There was one panel meter with 4.5 digits and *no* accuracy spec. What's the point ? Why have 4.5 digits unless you can brag about it ? Maybe two of the digits read "00" all the time ?

Yes, you can add two meter readings together.

For the ops purpose, motor current, you don't need

But there are many ways to do this properly, they're sitting on Amazon right now, and they have no specs...

You have to switch over to a real supplier, Digikey, Element 14 or whatever, and find a supplier with specs.

You should be able to buy metrology with specifications just like the specs that come with a multimeter. There is usually a page or two with "+/-1% and 3 digits" type specifications. You want to buy a product with specs. Some day, you may need the accuracy.

Paul

So re-reading your text, you use the dynamo to start the engine?

Bill

These days a lot of consumer products have >1 sets of specs that contradict each other :)

But the ones to beware of are when they agree - then they're lies. I can only hope the move away from China might solve this.

PS no need to buy a shunt, cut a food can. Metals change R as they get hot but are good enough for many jobs. Dunk em for better accuracy. And don't use ali for current shunts, the oxide is a problem.

NT

I used the power from my dynamo to drive the starter motor in the other car.

Jim

Ever thought of converting to an Alternator?.

Did this with several old cars over time and it worked very well:)...

Hasn't it always been and what are the specifications that we should really question?

Buy a 4 jewel watch or a 8 jewel watch? How many are just stuck inside of the case rather than being used as bearings surfaces?

Anyone remember the early front panel marketing for CD players, the more bits for the DAC quoted on the front of the box the better the player! A "48 bit" player may have only had a single bit DAC.

Obviously an amplifier that quotes music power rather than RMS power is better because the numbers are much bigger.

Is a 20 mega-pixel camera better than a 10 mega-pixel camera? Probably not if the overall detector size is the same. The latter could have a better sensitivity and a better signal to noise margin.

Can you really hand hold a camera with a x15 zoom as shown in the adverts?

Those cheap (£3) panels meters from china are possibly no better than 5% accurate, but maybe better. The chances are that they all use the same IC which requires a couple of non-critical external components. The precision reference and comparison circuits are all inbuilt in the IC. I agree that not quoting a specification should be a major warning sign about purchase if the item is intended for serious measurement rather than just a handy-wavey indication but if you don't want to spend maybe

As for just lying about specifications just go on Ebay and just look at the quoted specifications for some rechargeable AA and AAA batteries and the specification for replacement phone batteries that will last 4x longer than those fitted by reputable manufacturers. A single AA battery is now capable of powering an electric car for 250 miles!!!!

I have kept the car configured as it was when it left the factory, and the dynamo and control box combination works OK (and I have a spare dynamo in my garage in case it is needed).

I am also aware that I could convert the electrics to negative earth, but I haven't done that either, though I have installed a cigarette lighter socket delivering a negative earth connection so that I can use a car battery powered tyre pump or other gadgets like a Satnav which require that polarity.

Jim

Converting to negative earth will reduce corrosion, and is worth doing for that reason alone. The only reason not to do it is of the existing factory fitted radio needs a positive earthed supply.

It does not affect the originality, and is easily reversed.

how does that work exactly?

I think my irony meter just went FSD...

That was me. When I first got my (Diesel) ?koda Felicia (far from new! But I presume it had recently had the 'plugs replaced), it seemed to start within a quarter of a turn, if I waited for the light to go out before cranking; I'm not exaggerating, it really did seem to fire as soon as the engine was turned. It progressively got harder to start, so I eventually had them replaced, which brought it back to similar (though not quite as good). I don't think it had any fancy diagnostics, though if your neighbour's is modern, that might have.

(I loved the "peer pressure" response!)

Ah, so I guessed wrong.

It always struck me as odd - especially in the days of dynamos - that cars had the two devices; surely one could serve as both. Presumably the design differences needed for operation at different speeds/durations made it less bother just to fit two devices. []

There was a car in the 60's that had a unit doing both jobs. Was it the Beetle?

Trouble is trying to do 2 jobs it likely does neither well. Starters are quite low geared but dynamos about engine speed. At least 1 cheap (eastern-european?) car had a combined starter-dynamo. I can't remember the make. As a car tinkerer I was asked to look at 1 by a co-worker, took 1 look at the manual and declined.

Paul.

Well, my Messerschmitt KR200 has a 'Dyna-Start' unit that does both and does so pretty well (in that it's never been a problem)?

It's also interesting that it can also start and run the engine both ways, giving you 4 speeds in reverse. ;-)

Not sure it could be classified as a cheap car though, then or now, more expensive than a Mini at the time I think?

;-)

Cheers, T i m

These young 'uns won't understand FSD...

My brother bought an old Gogomobile in the 1960s, dirt cheap because it was advertised as a non-runner and he had to get a friend with a car to tow it round to his house. It was a Gogomobile Royal, like this

Then the way the engine started was a puzzle, because there was no sign of a starter motor, or any kick start mechanism but there was a diagram showing that there was a "lichtsmaschin" (I can't remember exactly how it was spelt) on the front of the engine underneath some airflow cowling for cooling. That was wired through some complicated relay arrangement to the ignition switch and the battery. When the key was turned it operated a relay and connected the battery to one set of wires going into the cowling, and when the key was released it dropped the relay and connected another set of wires to the battery. It was a single device attached to the crankshaft that turned the engine to start it and one started it charged the battery.

After charging the battery and winding the engine over for a while for the mechanical pump to get the petrol from the tank to the engine it did start.

Gogomobiles were made in a Bavarian factory, so not quite eastern European, and BMW bought the company in 1967 to gain ownership of some useful patents.

Jim

If he thinks this thread does demonstrate the group's understanding of electronic basics maybe he could moonlight as a standup comedian. Some do but so many replies show no grasp of elementary stuff.

NT