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Charging system help

Posted: Fri May 23, 2014 2:31 pm
by finallyrunning
I'm currently running a battery in the trunk with a painless Killswitch relay, 100 amp alternator on a 5 crank inch pulley from jones racing. I have a 900 cc battery with 1000 reserve capacity the issue is that the alternator is not keeping the battery charged when running fuel pump water pump and fans. That's not including running headlights brake lights turn signals that I would be using that night for street driving. Am I not spininng the alternator fast enough. Or is that 12 gauge painless wire that runs to the back to charge the battery not enough? It does charge, I can cruise around for a few hrs. But when I get home and check the battery it only has 46 % charge.
Any ideas?

Re: Charging system help

Posted: Tue May 27, 2014 7:45 am
by Bruce69Camaro
I'm going to say you need a bigger line going back to the battery.

I'm running a 6 awg wire back to mine and I think I was told to use 4 awg. I know some that run bigger.

There is a good chart online that shows you what size line you should use, but I can't remember where it's at, maybe someone can help find that link?

Just to be safe, add up all of your amp draw and make sure your alternator is big enough. I'm using a 105 amp and it sound like you should have enough.

I'm running a 5.4" pulley and I'm showing 14.1 volts at an idle, with you pulley, you should be good enough. I was also running a 4" pulley and that was border line, running 13.9/14.0 volts.

Make sure all your components are grounded good too. I run a ground bar and have everything hooked to that.

But I'd start with a larger chargering cable going back to your battery.

Re: Charging system help

Posted: Tue May 27, 2014 5:25 pm
by finallyrunning
Okay thanks that's what I was probably thinking I just can't understand why the painless shut off relay has such a small wire that supposed to run all the way up to the alternator. I have the kill switch relay in the trunk near the battery you think the six AWG wire run back to that relay would be fine ?

Re: Charging system help

Posted: Tue May 27, 2014 5:45 pm
by Bruce69Camaro
I'm running 6 awg and been told I should be 4 awg but I haven't had any issues
but your running more stuff then me so maybe 4 awg would be better. I wish I
could remember where that wire size chart was at.....

Re: Charging system help

Posted: Thu May 29, 2014 9:32 am
by finallyrunning
Okay thanks a lot. I have the wiring chart that you're talking about. But that four or six awg wire is going to run to the painless shut off relay before it gets to the battery. Which the 6 awg is down to 12 again. But at least it'll be a step in the right direction

The 14.1 volts you're pulling is that at the battery in the trunk or behind the altenator?

Re: Charging system help

Posted: Thu May 29, 2014 10:44 am
by wheels
One thing you should be sure of it the difference of the voltage reading from the alternator output connection to the voltage reading at the battery. Should be less then .5vdc or the closer the better. The Power Master website has great info regarding this.

Re: Charging system help

Posted: Fri May 30, 2014 11:48 pm
by wikd69
I ended up having to go with a 140 amp single wire and run a dedicated 2 gauge (I think it was 2 gauge) from the alternator all the way back to the battery. I use a separate much heavier cable running forward to a master switch up front. Measure and add up all your amperage draws - you might be surprised. I added a Lincoln Mk VIII electric fan and the damn thing pulls around 40 amp all by itself.

Re: Charging system help

Posted: Mon Jun 02, 2014 4:34 am
by finallyrunning
Okay great sounds like some good stuff but I'm still stuck on the one question that painless master shutdown relay do you hook your 4-6 or two AWG wire up to your painless cut off relay or are you running it right your battery.(which will keep case running) If you run it right to your battery or battery switch. The reason that's there is to keep the master cut off switch from spiking the ignition box. Right? And if I run that wire through the painless relay I'm hoping I'll still get the 14.1 charging at the battery

Re: Charging system help

Posted: Tue Jun 03, 2014 5:02 am
by Bruce69Camaro
finallyrunning wrote:The 14.1 volts you're pulling is that at the battery in the trunk or behind the altenator?
Sorry, forgot to answer this, I measured this at the battery, which was in the trunk and at an idle.

Re: Charging system help

Posted: Wed Jun 04, 2014 12:59 pm
by bracketchev1221
I have 4 gauge from the alternator to the battery side of the cutoff switch. 12 gauge is not enough for such a long distance. I would bet the 12 wire is getting hot and the resistance is going up in the wire as the battery goes dead.

Re: Charging system help

Posted: Mon Jul 21, 2014 9:02 am
by finallyrunning
Ok. Final update.
The painless shut down relay that I had was the 30amp relay ( which I think they don't sell anymore) so bought the new 250 amp shut down relay that comes with 8 gauge wire from alt to relay and from relay to battery side of cut off switch.
Got 12.80 at the alt, and 12.35 in the trunk at the battery. Drove the car for about 30 mins with fan,wp,fp, parking lights. And battery was at 95% when I got home.
Prob solved (I think).
So thanks for all the input and help. Soon be at the track

Re: Charging system help

Posted: Mon Mar 06, 2017 9:04 pm
by finallyrunning
Hi everyone......
I'm back.......unfortunately...... still having problems.
if you have been courteous to read and post on my problem thank you.

update 8awg wire battery to 140 amp alternator. good 8 (must need 6?) awg gound wire from battery to roll bar, to each cylinder head, to block, to alternator housing, to core support.... changed alternator pulley to smaller pulley to spin it faster at idle. get 13.4 at alternator 12.8 at battery I trunk.
my voltage drop is not bad. but even with 140 amp alt. it still drags battery down.

was told by magnflow tech(getting fuelpump rebuilt) go 16volt or 2 batterys ( no room for 2) . really considering the 16 volt system. just have found all kinds of different opinions on the net.
to much wear for ignition systems for a street car and accessories ,etc

can someone point me to a good article on how to convert from 12 to 16. what I need to protect etc

or anything I'm missing I've wired a dozen racecars no problem..... my car??? go figure!!!!!! haha

thanks everyone this is a great reference.

Re: Charging system help

Posted: Tue May 30, 2017 10:50 am
by wheels
In my experience and opinion a 140 amp alt is more then enough. The alt should put out 14 VDC with a fully charged battery. Make sure the battery is actually good, charge it then check the volts. If anything less then 13.5 out of the alt, the alt may have an issue.
Your previous post about the 12.8 and 12.35 levels, the drop (the 1/2 volt drop means the wiring should be ok) isn't terrible but the levels are, with that alt you should not be below 13, there should be no way it's working that hard....unless you have something drawing a lot of current....or the battery is fried....Remember the alt is not supposed to charge a dead battery, it can but it's not meant to...