Why an Ammeter?

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Model T Ford Forum: Forum 2015: Why an Ammeter?
Top of pagePrevious messageNext messageBottom of page Link to this message  By Paul O'Neil, Fullerton, CA, USA on Thursday, February 05, 2015 - 05:06 pm:

In addition to the ruminations on gearing posted on another thread I often wonder why Ford choose to furnish an ammeter as the sole instrument on the instrument board.

As I understand it, the third brush was to be set for your average driving balance of using the headlights or not. If you thought that the battery was fully charged you needed to run the headlights in the daytime or risk boiling the battery. Batteries already had short lives in those days typically being replaced every year.

It would seem to my electrically challenged mind that a battery charge state indicator (volt meter?) would be more useful.

Why the ammeter? How was it supposed to be used back in the day?

BTW, in my own car I have both the Fun Projects ammeter & voltage regulator which I was able to install by myself just by following the directions. They work perfectly and I think are taking good care of the 6v Optima battery.

Vintage Paul, rudimentary electrician


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ken Kopsky, Lytle TX on Thursday, February 05, 2015 - 05:52 pm:

For one reason, there's no provision to use a volt meter with the switch design. It would be on all the time. It could be wired to the generator output side of the cutout but that's an extra wire and it wouldn't indicate battery charge state. It would simply show the output from the generator.

How did you wire yours?

Did you use the improved switch panel below? :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Paul O'Neil, Fullerton, CA, USA on Thursday, February 05, 2015 - 06:17 pm:

Hey Ken! I'm still enjoying the nickel plating on the steering box. It looks great with the powdercoat on the column.

I have no volt meter nor with the Fun Projects items feel any need for one.

From my very limited understanding of electrics I would have thought that a meter to tell the state of battery charge (voltage?) would have been more useful with the stock cutout. It seemed to me that such a gauge would tell the driver when the battery had had enough so he could switch on the headlights and avoid boiling it.

I'm just guessing . . .

Vintage Paul


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ken Kopsky, Lytle TX on Thursday, February 05, 2015 - 06:34 pm:

A volt meter could be used. It's just that a switch would be needed to turn off the meter circuit. Which is, I think, how the FP instructions read. A push-button switch would work great. When you want to read battery voltage, just push and hold the button. Releasing the button would disconnect the meter.

Or you could really get fancy and run the meter from the battery through a small relay powered by the generator. When the engine was running, the meter would indicate battery voltage. When the engine is off, the volt meter circuit would disconnect.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Paul O'Neil, Fullerton, CA, USA on Thursday, February 05, 2015 - 07:27 pm:

Just a clarification, the FP unit is an ammeter which I have coupled with their voltage regulator - the bit that replaces the cutout.

My curiosity is only about why Ford installed an ammeter which would appear to be less useful than a meter to inform the driver about the state of charge of the battery which might be helpful in deciding when to run with the lights on.

Vintage Paul


Top of pagePrevious messageNext messageBottom of page Link to this message  By JohnH on Thursday, February 05, 2015 - 08:26 pm:

The ammeter really just shows that the generator and cutout are functioning. Imagine if the cars did not have one. You could be driving around for a week with an inoperative charging system and be caught with a flat battery. At the time, it would have been cheaper to use an ammeter than the circuit for an idiot light.
A voltmeter is only useful to a limited extent. It will not show if the battery has reduce Ah capacity, nor will it show if the battery has high internal resistance, unless the battery is under load.
A battery with a shorted cell, for example, will still show a charge at 7V if one of the other cells has gone high resistance.
Also, consider that the cost of a sufficiently accurate suppressed zero voltmeter at the time would have probably cost more than a regulator for the generator. Ford used the third brush method because it's cheap - electromechanical regulators of the type used up until recently were available at the time and used in other cars.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Thursday, February 05, 2015 - 09:02 pm:

Without the ammeter, you would drive until the battery went dead before finding out the generator was not charging. All cars with generator had an ammeter until sometime in the late 1950's when the idiot light replaced it. Then you would only know the generator (alternator) was not working if the light came on. I think the reason for the light instead of ammeter was because with a voltage regulator, one would see many amps charge and followed by almost zero amps. That was confusing to the average motorist, so the light was just a positive indicator of lack of charge.
Norm


Top of pagePrevious messageNext messageBottom of page Link to this message  By Gary H. White - Sheridan, MI on Thursday, February 05, 2015 - 09:31 pm:

Best use of a voltmeter is to use it with the engine off and the headlights on. The head lights provide a load that will better show a deficient battery.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Friday, February 06, 2015 - 12:55 am:

Without an expanded scale type meter, it is rather difficult to get a very exact reading and with batteries the voltage range of interest is rather narrow being just below 6V to just over 7V. If this were displayed on say an 8V full scale meter it would not be something you could read at a glance and tell what was going on like you can with an ammeter. Furthermore if the battery were down a bunch and you watched only the voltage you could damage your generator since its charge rate was limited to about 15 Amps so you could be charging at over 15 amps and not know it until you smelled or saw smoke from the generator. The adjustable 3rd brush had its limitation but it worked well enough that people bought it to have the starter and simply put up with its shortcomings. VR's and expanded scale Voltmeters were not simple to make with electro-mechanical means which is all they had during the T era. Personally I think the electrical engineers did a pretty darn good job with the T's electrical system and especially given what they had to work with.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ken Todd, ............Red Deer, Alberta on Friday, February 06, 2015 - 11:31 am:

Methinks the reason that the manufacturers went to an idiot light in the '50s was simply to cut costs and improve their bottom line.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Paul O'Neil, Fullerton, CA, USA on Friday, February 06, 2015 - 11:48 am:

Thanks guys, I think I understand why the ammeter was used now.

How did drivers manage the charge of the battery? How did they know when it was full and that it was time to turn on the headlights?

Vintage Paul


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dick Fischer - Arroyo Grande, CA on Friday, February 06, 2015 - 11:54 am:

I agree that the ammeter is most useful for managing the battery charge. By selection of hi beams, low beams, or parking lights on my Model A I can set the charge just above zero for extended driving.

But, like Paul, I always wonder how long I should drive on full charge before cutting back with the lights.

Dick


Top of pagePrevious messageNext messageBottom of page Link to this message  By Paul O'Neil, Fullerton, CA, USA on Friday, February 06, 2015 - 01:32 pm:

There musta been some sort of simple rule of thumb if nothing else back in the day. Many new Ford owners would have had little experience with mechanical issues and would have needed guidance to decide when to charge & when to turn on the lights.

On my Flivver I have the FP VR so I don't worry but on the two Hudsons with cutouts its by guess & by golly.

Vintage Paul


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Friday, February 06, 2015 - 02:41 pm:

Paul:

In truth the whole battery market was different. There was no rule of thumb and Ford simply copped out by telling customers to match the charge rate to their driving habits. Before about 1939 Battery shops were on every corner and batteries were changed very often. Ford like many others thought that the problem of short battery life was caused by UNDERCHARGING of the battery so for the Model A they came out with a POWER HOUSE generator that could easily more than double the charge rate of the ordinary generator used prior. That proved to be a bad idea since it merely destroyed batteries even quicker and also ammeters and wiring if one was not careful. Finally they started to look for something to control the generator output dynamically and that was found to be the vibrating reed type of mechanical VR. They worked but had a very wide range of voltage over which they could be made to work. This gave rise to VR outputs being considered OK with output voltage ranges from 6.8V to over 7.5V which is why a lot of guys today wreck their batteries still because they insist that the VR should put out 7.5 since all old car people always think that "MORE IS BETTER" but it isn't. Today the modern VR can track not only the ideal Voltage for the battery but also even change that voltage based upon surrounding temperature which is desirable for even longer battery life. The VR's I make are in fact temperature compensated since it really didn't add anything to the cost of the VR to do that. Since a T only starts the car and it runs on magneto after that - the battery should be recharged in a matter of minutes and one should get a very very long life from a T battery unless the battery is overcharged.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dick Fischer - Arroyo Grande, CA on Friday, February 06, 2015 - 03:21 pm:

As a kid I recall that most gas stations ("filling stations") had a special jug for filling batteries, and the attendant would check the specific gravity of your battery if you asked. Maybe that's how a person learned to regulate his charge rate -- by the attendant telling him if his battery was low or high on SG, and if he seemed to need more battery water too often.

Dick


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