Alternative Alternators ?

[Charlescrown]

Have you done an output test on the alternator to find out how much it can put out? I would think 85 would be more than enough in that car. Don't know what your running to draw so much current. I would measure the voltage at the battery and if it's less than 14 put the diode in the sensing wire to step it up.

[immortality]

Yeah, I think 4ga over the length of the run should see you right.

[immortality]

The current rating is not really what you want to look at in this case. While a '50A' cable could carry more over a short distance and have no problem, the voltage drop becomes significant over the distance you have to run it. Losing near on a volt over the cable becomes an issue for charging a battery!

Some quick calcs using some wiki cable resistances at 50A over a 6m distance, 8ga loses around 0.6V, 4ga loses 0.2V. At 80A its 1V and 0.4V.

Not all cable is created equal either, look out for the rubbish cable with a heap of insulation to make it look like thick cable.

Moving the sense wire to the battery or putting a diode inline with the sense wire can help if its still a problem. A diode increases the charge voltage by around 0.7V.

This is spot on, however he's probably trying to pass a lot more than 50amps through said cable so I would imagine the voltage drop would be even greater. Heat increases resistance which creates more heat and becomes a vicious circle and hence the reason I suggested he check the cable temp as it's a good indicator to how well the cable is coping with the load. At work we get a guy with a thermal camera in once a year for this exact reason, it a reliable method to quickly find issues with anything electrical.

The Jaycar cable is the good stuff. The other good stuff is electrical welding flex, it has the proper cross-section to suit the load and it's double insulated but it's not cheap.

It's funny you mention the diode, almost all the V6 alternators I have ever tested sit @ about 14 volts but struggle to get much more. A lot of the more modern calcium hybrid type batteries also like a slightly higher voltage.

[Holden202T]

Don't know what your running to draw so much current. I would measure the voltage at the battery and if it's less than 14 put the diode in the sensing wire to step it up.

2 x bosch 044 pump (approx. 16amps each max) = 32amps
1 x carter lift pump (around 10 amps)
2 x thermo fans about approx. 5 amps each) = 10amps
6 x LS2 coils - now im not sure on these but from what I can find on the net about 4amps each) = 24amps

so that stuff is going to pull 76amps (max) then there is whatever is needed to run the computer, ignition module, and all the other electrical bits and pieces, and that's before the lights are on! (whats a standard H4 bulb normally use??)

I think the main issue is the battery charge terminal is probably only going to supply 40-50amps at best, that's assuming it doesn't loose too much over the 5mtr odd length.

I have checked the alternator and there is 14.2v I think it was at the back of it, and there was about half a volt lost across the run to the rear of the car .....

I can always pump it up with the diode if needs be if a larger lead and sense wire to boot don't fix it.

[immortality]

It really is a shame you have to send all the electrical power to the back and then front of the car.

[Holden202T]

hahaha yeah theres always a compromise, I didn't want the isolator in the middle of a panel and so the back of the boot was the best option at the time!

[The1]

The current rating is not really what you want to look at in this case. While a '50A' cable could carry more over a short distance and have no problem, the voltage drop becomes significant over the distance you have to run it. Losing near on a volt over the cable becomes an issue for charging a battery!

Some quick calcs using some wiki cable resistances at 50A over a 6m distance, 8ga loses around 0.6V, 4ga loses 0.2V. At 80A its 1V and 0.4V.

Not all cable is created equal either, look out for the rubbish cable with a heap of insulation to make it look like thick cable.

Moving the sense wire to the battery or putting a diode inline with the sense wire can help if its still a problem. A diode increases the charge voltage by around 0.7V.

This is spot on, however he's probably trying to pass a lot more than 50amps through said cable so I would imagine the voltage drop would be even greater. Heat increases resistance which creates more heat and becomes a vicious circle and hence the reason I suggested he check the cable temp as it's a good indicator to how well the cable is coping with the load. At work we get a guy with a thermal camera in once a year for this exact reason, it a reliable method to quickly find issues with anything electrical.

The Jaycar cable is the good stuff. The other good stuff is electrical welding flex, it has the proper cross-section to suit the load and it's double insulated but it's not cheap.

It's funny you mention the diode, almost all the V6 alternators I have ever tested sit @ about 14 volts but struggle to get much more. A lot of the more modern calcium hybrid type batteries also like a slightly higher voltage.

thats cause they run a 14v regulator

[immortality]

They are 14.4v regulators yet I regularly see high 13's only especially if it's an older vehicle. Even brand new alternators showing only 14.1-14.2 if you're lucky. Then you need to account for voltage drops through the various items in a wiring loom and things don't looks so great.

I did have a play around with a hot-earth system on my old VN and found 0.3 volts (@ the battery) even though I had gone through all the factory earth points cables/connections etc.

[Charlescrown]

Looks like from those figures you are maxing out and I am inclined to agree with you and fit a bigger alternator. Boy the one fitted must be getting a little hot. I have run alternators to the max on a test bench and they start smoking.

[Holden202T]

well the alternator "should be capable" of 85 amps .... so i am more leaning towards the charge cable or sense cable is the issue rather than the unit being maxed ....

also keep in mind while i've listed max amps of all the stuff in the car, its not that often that they are all using the max at the same time, for example, the second pump is only on under boost, so that is at the most only for 7-10 seconds at a time anyways, then the lift pump is not actually under pressure so it might never see max ..... then thermo fans probably only see max on start up ? .... as for the 6 coils, they are all changing duty cycles all over the shop, same with injectors and the like so there are alot of variables....

im fairly confident that the charge cable needs an upgrade, so i want to do that regardless, and in doing that first i can fairly quickly and easily see how much difference it makes in the shed idling without having to have it racing ..... and honestly if it runs only off the battery for a drag run then charges the rest of the time that is "acceptable" and a marked improvement on what i am seeing now.

also found some more info on the LS2 coils which says that i'd likely see a max of 10amps per set of 2 (3 x 2 sets in wasted spark) ... so might be seeing up to 30amps from them..... fair difference to the single coil, but you need it for a better spark i guess