Original Style W116 Battery

[ptashek]

OK.. silly question maybe, but a 74Ah battery, when measured with an ammeter, engine running, and engine off.. Would the ammeter always read 74ah? What about the alternator in a W116? Was that one designed to even charge up to 74ah, or is that only related to voltage?

The ammeter wouldn't show anything useful.

A voltmeter would show somewhere between 13.8V (engine on, healthy alternator) to 10.8V (engine off, flat battery). You should never see more than 14.4V across battery terminals with the engine on. If you do, the voltage regulator in the alternator is shot.

The 74Ah capacity rating means a fully charged battery, in theory, can supply 3.7A of current for a continuous 20h at room temperature, before reaching full discharge voltage. Capacity is not something you'd measure with an ammeter.

The alternator in a typical W116 is rated at 55A at the regulated voltage, which would be around 13.8V.  That's what's supplied to the battery terminals with engine on, to charge it up, and to all other units to run them. It'll charge any automotive 12V battery just fine.

There's also the cold cranking amps rating, which defines the maximum short-burst current the battery can supply at some specified operating temperature, without being destroyed.

[floyd111]

Yes, indeed. I should have known the answer to this one myself. A and ah are not the same. Silly.
So, my ammeter would be showing whatever my alternator is generating in amps?

If that is the case, this would bring me to the next question.. Did MB offer a variety of alternators for their W116?
I would think that if they went to the trouble of commanding a 70A VDO ammeter, they would have wanted that dial to stay nicely at the 70A mark, not?

[ptashek]

Yes, indeed. I should have known the answer to this one myself. A and ah are not the same. Silly.
So, my ammeter would be showing whatever my alternator is generating in amps?

If that is the case, this would bring me to the next question.. Did MB offer a variety of alternators for their W116?
I would think that if they went to the trouble of commanding a 70A VDO ammeter, they would have wanted that dial to stay nicely at the 70A mark, not?

Your ammeter would show close to 0, unless you connect it in series with an active receiver. I think you're confusing voltage and current. If you put a voltmeter across the output terminals of a running alternator, it should read ~13.8V DC on a healthy unit. Input is three-phase AC.

I'm not sure if there was a higher rated alternator available for the W116. Some people upgrade to W126 units, which are rated at ~90A.

[Peter]

I've seen both the standard alternator and a high amp alternator advertised fro the W116, not sure that the higher amp alternator is a true option but I guess it might have been if you ordered your W116 new with telephone, fridge, reclining rear seat etc etc. The listings were on Ebay USA.

[floyd111]

Your ammeter would show close to 0, unless you connect it in series with an active receiver.

There must be such a receiver, or the ammeter would serve no purpose. With all the heavy equipment draining amps, that ammeter was not a luxury.
VDO supplied this ammeter with an inbuilt shunt (whatever that does or mean.)
So, is that receiver not in that ammeter?

Brief.. where does one connect the ammeter cables, to what unit, in order to get a proper amp-reading?
Since I am not an electrician, nor a mechanic, I can't be sure. Also, since that ammeter seems to not-exist in the EPC, I am not sure I can track that data from parts fiches either.
I CAN contact the VDO company that supplied those ammeters to me. They should know..I hope.

[ptashek]

Your ammeter would show close to 0, unless you connect it in series with an active receiver.

There must be such a receiver, or the ammeter would serve no purpose. With all the heavy equipment draining amps, that ammeter was not a luxury.
VDO supplied this ammeter with an inbuilt shunt (whatever that does or mean.)
So, is that receiver not in that ammeter?

Brief.. where does one connect the ammeter cables, to what unit, in order to get a proper amp-reading?
Since I am not an electrician, nor a mechanic, I can't be sure. Also, since that ammeter seems to not-exist in the EPC, I am not sure I can track that data from parts fiches either.
I CAN contact the VDO company that supplied those ammeters to me. They should know..I hope.

A shunt is just a fancy name for a resistor resistance built into the unit, which creates a voltage drop across it's terminals that allows the unit to measure the current.

I have several wiring diagrams and neither has that ammeter in it. If anyone knows exactly, it would be MB or VDO.

Normally a car ammeter is put in series with the positive output terminal of the alternator and the positive battery terminal.