Current meter

[John Orentas]

Martin.

 

Quote Martin.

 

"If the battery was drained on a cold morning trying to start this Sierra, then the alternator would give its all (at least for a while) and be charging at about 100% of battery capacity".

 

It doesn't work like that. The 90 amp rating of the alternator must be seen as a 'maximum' output' it would never try to put a 90 amp charge into a single battery.

 

In fact I am not sure that an alternator rated at 90 amps can be regarded as a continuous rating at all, I have been trying to find some data on this. It is possible that a 90A unit can only output say 60A constantly.

 

Going back to the Sierra, going along in daytime with little electrical load and a fully charged battery your 90A alternator would be outputing about 3 amps.

[David Schweizer]

John O, I can assure you that my system is not like the Tardis, the ammeters just work normally without any attention from me, and the volmeter switch is normally set to the OFF position and is used ocassionally to check whether either of the batteries are beginning to run low. I don't see the point of having a voltmeter working when the engine is running, unless you want to monitor the charge voltage, which is pointless as that is moniored and regulated by the Alternator controller.

 

I am sure that the man in Hanneys (Radio Spares Shop in Bath) said it was a shunted meter. It is a rectangular analogue meter and there is a capacitor (or is it a resistor?) either linking the two conatcts, or between one of the contacts and the connection to the switch. (I cant remember which offhand) The man in the shop said it was something to do with it being a 12volt meter. Anyway it works and it only cost a couple of Quid.

 

I am not particularly well informed on electronics so rely upon the advice of those that are. My skill (such as it is) is limited to being able to make up circuits from diagrams provided by someone else.

[buggsy]

I wonder about this charging rate too.

10% of my (now) 440AH is 44amps

(bear with me - it is my last day before Christmas!)

My 90amp alternator came off a Sierra 2.3l diesel - with a single battery.

If the battery was drained on a cold morning trying to start this Sierra, then the alternator would give its all (at least for a while) and be charging at about 100% of battery capacity.

The alternator controller manufacturers seem to have completely ignored this percentage of capacity idea - why?

 

I will be buying a Sterling/Prestolite package of controller and alternator together - the Prestolite alternator being rated at 110A.

I would need 10 batteries for this to balance out (at 110AH each) - or five if you go by the 20% version of the equation.

Yeah - OK - you're pretty close as I would actually have six.

 

Will certainly look at Driftgate but they don't seem to have much of a name - I for one have never heard of them!

 

M

<{POST_SNAPBACK}>

[buggsy]

Just to add even more confusion to this subject have you considered the latest alternator to battery charger from Sterling?

[Guest]

Once saw a device on the net where a car alternator was driven by a lawnmowwer engine. The interesting thing was they were using a wire wound potentiometer to control the field wihin the alternator instead of just a low wattage lamp. Obviously it required human intervention, but was presumably a crude sort of alternator controller. It was claimed that by regulating the field, that the voltage and current could be regulated during charge.

[khaffra]

A shunted voltmeter is an Ammeter, They are commonly known as shunted voltmeters when they have external shunts, all ammeters have a shunt or resistor somewhere in them and then actually measure voltage across this resistor or shunt.

A shunt is just a known value resistor which the voltmeter scaled as an ammeter reads the voltage across. (works using ohms law).

If using an external shunt it must be the correct value for the meter otherwise you will get errors in your readings.

[maffi mushkila]

Once saw a device on the net where a car alternator was driven by a lawnmowwer engine.  The interesting thing was they were using a wire wound potentiometer to control the field wihin the alternator instead of just a low wattage lamp.  Obviously it required human intervention, but was presumably a crude sort of alternator controller.  It was claimed that by regulating the field, that the voltage and current could be regulated during charge.

 

The output of an alternator is governed by three things

 

1. Field strength

 

2. Speed of rotation

 

3. Number of conductors rotating within the Field

 

So a potentiometer or more usual a rheostat is is suitable as a controller if you have the time to sit and adjust it all the time the alternator is running.

 

Years ago generators (in aircraft) were controlled using a stack of carbon washers in series with the field under the influence of spring pressure on a soft iron core pressing on the stack, which was opposed by a magnetic field produced in a coil by the output.

 

On start up the stack was compressed (min Resistance) as the output increased the magnetic field in the coil pulled against the spring decompressing the stack, increasing the resistance, reducing the field current. At operating voltage the coil field strength would be equal and oposite to the spring pressure holding the pile of carbon washers mid way between fully compressed and fully decompressed when the operating voltage was reached the regulator was in equalibrium.

 

 

Adding a load to the generator would drop the output, consequently the voltage across the coil would drop reducing the current through the coil allowing the spring to compress the pile, reducing the resistance, increasing the current through the feild so increasing the output. As the output voltage increased the coil current would increase, the magnetic pull against the spring would increase so reducing the the spring pressure on the pile until everything was again in equillibrium.

 

The difference between fully compressed and fully decompressed was about 0.4mm of movement of the soft iron core.

 

See I have nothing to do again.

[weeble]

Years ago generators (in aircraft) were controlled using a stack of carbon washers in series with the field under the influence of spring pressure on a soft iron core pressing on the stack, which was opposed by a magnetic field produced in a coil by the output.

 

<snip>

See I have nothing to do again. 

<{POST_SNAPBACK}>

 

Yikes! the old B2 Carbon Pile Regulator Maffi? That takes me back a bit.

 

When are you going give the lesson on Mag-Amps?

 

Even less to do today than you

 

Cheers.... mike

Edited January 12, 2005 by weeble

[weeble]

Yikes! the old B2 Carbon Pile Regulator Maffi? That takes me back a bit.

 

<{POST_SNAPBACK}>

 

Ooopss..... After lunching with a former service colleague I've been assured I really meant to refer to a "type 23" regulator. Wasn't the B2 (or was it P2) the associated generator?

Ah well, it's true what they say about memory fading with age

Whatever they were called, I remember them being a bu**er to set up on the bench!

 

Cheers.... mike

 

P.S. whatever, it does prove what little I have to do today when pub conversation reverts to such matters.

[maffi mushkila]

Ooopss.....   After lunching with a former service colleague I've been assured I really meant to refer to a "type 23" regulator. Wasn't the B2 (or was it P2) the associated generator?

 

 

P3 generator. Close but no banana.

 

Now Mag amps what an amazingly simple piece of equipment.

 

Here's a funny story.

 

The first comissioned female engineer to teach at 1 Sof TT went to great pains to inform students that Mag Amps were old fasioned and not used in aircraft anymore so they didn't have to know about them.

 

This was about the time the Tornado came into service, you've guessed it the flying Mag Amp store.

Edited January 12, 2005 by maffi mushkila

[weeble]

P3 generator. Close but no banana.

 

<{POST_SNAPBACK}>

 

P3. You're absolutely right Maffi..... I'll win back my beer in the pub tomorrow lunchtime

The second pint will depend if I can remember if I came across them on Meteors or Shackletons.

Better go before this thread is moved to the virtual pub.... can't afford to go twice in one day!

 

Cheers....

[maffi mushkila]

P3. You're absolutely right Maffi.

 

Of course!

 

..................... Meteors or Shackletons.

 

Meat boxes, Shacks had the B3278 me thinks.

 

How sad is that!

[weeble]

Of course!

Meat boxes, Shacks had the B3278 me thinks.

 

How sad is that!

<{POST_SNAPBACK}>

 

LOL..... Now the part number would be worth a chaser from the top shelf

[maffi mushkila]

LOL.....  Now the part number would be worth a chaser from the top shelf

 

I'm not that sad!

[FLIRKER]

John

 

Sorry if this is a simple question but regarding one of you original posts do you have any advice on where/how to wire in the ammeter.

 

Thanks

Al

[John Orentas]

Al.

 

A centre zero type is better as this will show the charging and discharging of the batteries.

 

Not easy to do this without drawing little sketches. You need the ammeter instrument itself, (it may be a digital or analogue type) and the matching 'shunt'. The shunt is basically a sort of resistor which forms part of your battery / alternator circuit, when current is flowing through the shunt there will be a very small voltage difference across it. It is this voltage difference* which is detected by the instrument and indicated as amperes.

 

One end of the shunt should be wired to the positive terminals of both domestic batteries, the other end will got to the alternator supply (the heavy cable) and all the appliances, lights etc. In practise probably to supply side of all the fuses.

 

Wired in this way a positive reading on the meter will indicate the charge from the alternator, when the engine is not running it will show the discharge of the batteries when loads are applied.

 

When the engine is running and the batteries are charging, switch on an appliance e.g. the water pump, you can witness how the regulator in the alternator 'balances' the load at the same time maintaining the charge rate.

 

*As the circuit goes from charge to discharge, the voltage difference too changes polarity.

 

The above will indicate the state of the domestic batteries only. Avoid running the starter circuit through the shunt, the very high current will grossly overload it.