P38 Battery charging improved

[javars]

As Im sure many have experienced in the last couple of weeks, the battery on my 4.6 has been getting slowly weaker (short journeys, everything on flat out) so Ive been hooking the car up to my oxford maximiser overnight every few days.
So I thought I would do a few checks, voltage across the battery with the engine running at 2000 was 13.4v but the voltage at the alternator was 14v. Switch the lights, fans etc on and it would dip to 12v. so basically there was hardly no charge going back to the battery on my journeys to and from work (4 miles)
So Ive fitted 2 extra leads, one from the alternator straight back to the + terminal on the battery and one from the - terminal to the alternator bracket. On retesting the was 14v across the battery, rising to 14.1v with revs. Switch on all the gizmos and I am still getting 13.5v
Will see how this week pans out and report back. Also made sure all the other earths were good afterwards but that didnt change the results.
Cost £9.48
Steve

 

[Datatek]

Typical corroded connections and cables problem. Good fix, should solve a lot of problems.

 

[jwaldron]

I don't get it. How would new connections between alternator and the battery increase the voltage across the alternator? I get how more voltage get from alternator too the battery, but not how it makes more voltage at the alternator itself.

 

[Ridesafe]

With good clean connections, not to mention less wire (resistance) to travel......simples! :high5:

 

[jwaldron]

With good clean connections, not to mention less wire (resistance) to travel......simples! :high5:

Not trying to be funny... but I still don't get it.

My comment was with regards to the amount of voltage generated by the altinator not how much resistance there is between altinator and battery.

I am not questioning the fact that more of what IS being created will get the the batery therefore charge it rather than just tickle it... but surely the connections in this case don't increase the Alternators ability to generate charge. For that to happen I would be expecting some sort of overhaul of the alternator.

Am I being stupid here... having a blond moment perhaps.

Plus resistance depends on the thickness of the wire not just the length, so a new thicker wire for example from lesser quality material as well even though shorter could increase the resistance not decrease it.. true?

 

[javars]

My meter only registered an extra .1 of a volt at the alternator with the new leads, maybe its was just the connection I made was a little better. Maybe its just my cheap old meter. But 5 days on there's no sign of the usual battery drop. Steve

 

[Datatek]

Not trying to be funny... but I still don't get it.

My comment was with regards to the amount of voltage generated by the altinator not how much resistance there is between altinator and battery.

I am not questioning the fact that more of what IS being created will get the the batery therefore charge it rather than just tickle it... but surely the connections in this case don't increase the Alternators ability to generate charge. For that to happen I would be expecting some sort of overhaul of the alternator.

Am I being stupid here... having a blond moment perhaps.

Plus resistance depends on the thickness of the wire not just the length, so a new thicker wire for example from lesser quality material as well even though shorter could increase the resistance not decrease it.. true?

Re read the posting, it was the voltage at the battery that significantly improved, not at the alternator. The resistance of cable and thus the voltage drop (assuming perfect connections) is the product of length and cross sectional area. Putting two resistances in parallel reduces the resistance as there now two current paths. So putting a new cable in parallel with the existing cable will reduce voltage drop giving a voltage at the battery that is closer to the output voltage of the alternator.

No matter what the quality of the new wire it will reduce the resistance as it is parallel with the existing wire.
The quality of copper wire for these purposes is pretty constant.

 

[Mike v.t.s]

id say get the alty checked, sounds like a diode or brush has given up so its not producing full power, also it could be a knackerd battery... first thing is drop test the battery... then start engine and see what ampage your alty is giving and what ampage your battery is excepting, i fooookerd battery wont acept the amps... so first check if the battery is ok etc etc

 

[Datatek]

id say get the alty checked, sounds like a diode or brush has given up so its not producing full power, also it could be a knackerd battery... first thing is drop test the battery... then start engine and see what ampage your alty is giving and what ampage your battery is excepting, i fooookerd battery wont acept the amps... so first check if the battery is ok etc etc

He was not talking about amps, he was talking about volts. If there is a large volt drop between alternator and battery you will not get the required amps

 

[dean68uk]

Ohms law V= IR

 

[Datatek]

Ohms law V= IR

Or V/R = I

 

[jwaldron]

Data; Hand up mate... I should have read the bloody thing correctly before going off all half cocked. Slap me - I've been naughty!!!

 

[dean68uk]

or v/r = i:d

:d

 

[Datatek]

Data; Hand up mate... I should have read the bloody thing correctly before going off all half cocked. Slap me - I've been naughty!!!

Just a Blond moment, not serious I need a bit of light relief I'm sat here writing frigging Christmas cards. :-(

 

[jwaldron]

Out of interest... what should a good voltage be across a good bat and then from alternator to bat??

secondly - if setting additional set of connections up in parallel help things... why isn't this std practice? or is it just a work around for a weak altinator?

 

[Datatek]

Out of interest... what should a good voltage be across a good bat and then from alternator to bat??

secondly - if setting additional set of connections up in parallel help things... why isn't this std practice? or is it just a work around for a weak altinator?

Voltage across the battery after running for a short time and assuming a good battery will be 14.4 to 14.8 volts. It should be near enough the same at the alternator and at the battery.

The aditional wires are nothing to do with the state of the alternator, they are to overcome bad connections or corroded cables. The cables on the battery can corrode inside the insulation where you can't see it which will reduce the current carrying capaicty of the cable

 

[Mike v.t.s]

He was not talking about amps, he was talking about volts. If there is a large volt drop between alternator and battery you will not get the required amps

Yes true true, but still if theres a diode or brush thats worn it wont be able to function at full power. i might of got a tad bit carried away with my post lol

 

[Datatek]

Yes true true, but still if theres a diode or brush thats worn it wont be able to function at full power. i might of got a tad bit carried away with my post lol

If the diode pack is breaking down, the amount of ripple that it can cause will probably stop the P38 from running at all, it could confuse all the ECU's

 

[sandyt]

which terminal on the Alt did you use for the +ve

 

[javars]

The same one that the positive leads already attached to. For those interested my batterys improved tenfold. I never get the feeling the starters slow now.