Alternator or battery issue

[Garybreadner]

The battery gauge swings from one side to the other with the engine running and I'm wondering if this indicates a problem with the alternator . Lately even after a short run the battery struggles to re-fire the engine. The battery is fairly new and I always have it on a conditioner. The kenlowe fan kicks in a 70 which is most all the time when I run it and I guess this is putting even more strain on. ( should I set it higher maybe 75-80) Thanks for any advise.

[MarekH]

Dear Gary,

There are two things you eed to get a handle on to guide you in sorting this out:-
1/ What is being measured?;,
2/ What is the benchmark measured against?

1/ The gauge is a bimetallic strip type which works by current passing through some heater wire which slowly makes a bimetallic strip bend and pull the needle across the gauge. Even if the voltage jumps from 0 to 12 volts instantly, the gauge will lumber across to the other side of the scale over a period of five to ten seconds. Put another way, the gauge only displays smoothed out changes which cause it to move.

That said, the label on the gauge is a misnomer. It does not measure battery voltage at all. It is fed by the green wire from the fuse board ("A"), which in turn is fed from the white wire from the ignition switch ("B") which itself is fed from the brown wire at the ignitoin switch ("C"), which comes through the loom from the terminal post ("D") and finally to the battery ("E"). The battery itself then has a spur to the alternator ("F").

The routing is important because it contributes considerably to the gauge reading. There are numerous bullet connectors and an igntion switch in the path and the resistance of the power circuit is not zero. This means that a voltage drop will be observed along the path proportionate to the current being carried along each stretch of wire.

For a last leg, the voltage that the gauge sees will be affected by the current drawn by all of the other gauges sharing the green wire. It'll also be affected by the voltage drop observed along the components using white wire on the way to its junction to the spur that goes to the gauge and so on and so on. The voltage drop across the ignition switch is recorded in the gauge and finally all of the car's electrics which share the common wire between the terminal post and the battery between D and E will affect the reading.

In short, battery voltage is ain't. If you see a substantial change in current draw along that chain, then less voltage will appear at the gauge if there is any substantial resistance in the wiring or connectors.

The gauge also needs to be earthed securely and by implication, so do the car's components which are along the common path used to supply the gauge.

2/ Once the engine is running, the alternator should take over powering the car as the alternator outputs 14 to 14.4volts rather than the battery 12.6 to 12.9 volts. Put another way, if the path from E to F or the earth return from the alternator to the battery are compromised then the gauge needle should move to reflect this.



The purpose of the radiator fan is to provide additional cooling as judged by a temperature operated switch which should be set high enough to only remain activated if the water being returned to the engine block is so hot that it's passage through the engine will result in the outflow exceeding a temperature that makes the mechanical thermostat remain wide open. Put bluntly, the radiator's job is to overcool the water such that the mechanical thermostat forces water directly back into the engine (rather than go to the radiator) to keep the engine hot. There is a constant yo-yo battle between the radiator and the thermostat as they are designed to do jobs diametrically opposite to each other and the radiator must always win.

It isn't obvious to me from your description what is going on, but there are a number of things to look at.
a/ You report that the battery struggles to refire the engine. If that is an accurate diagnosis then you probably have an alternator (or alternator wiring) problem as the battery is only designed to be used to start the engine, not run the car. (You may just have a poor fuel mixture problem for all I know.)
b/ You are using an aftermarket fan which may be too current hungry and being misused. If the water is cooled too much, then the thermostat closes and sends the water via the bypass directly back into the engine - there is no point running a fan at this point as there is no water circulating along the radiator loop. You basically want to cool the water only just enough to keep the mechanical thermostat cycling and no more - the mechaical thermostat combats any overcooling by design because that is its job.
c/ at low rpm, the alternator may not be active.

kind regards
Marek

[Garybreadner]

Thank you very much for your comprehensive reply Marek.
You have given me a lot to think about and try to Implement.
I very much appreciate your time and effort .
Gary.

[abowie]

The battery gauge swings from one side to the other

Do you have a voltmeter or am ammeter?