alt issues = 2 diffrent batterys ?

[brian84corvette 10+ year member]

hey guys.

trying to figure out some delima I have here.

battery under the hood is a optima yellowtop. I checked its voltage today with a dmm, and it was resting ( float charge - just turned the car off ) at 12.68

rear battery is kenetik 800 - resting at 13.36 - again just turned the car off.

both batterys are connected with 0 guage + and - and i use a pair of electrical cut off switches ( marine ) to turn off the + when I shut off the engine, so the back battery doesnt equlize with the front.

any how - when I start the car up cold, I get 14.2v

wich then turns to 14v in under 5 min. and after the car is warmed up or driven for more than 10 min. I have trouble getting the alt to charge over 13.7v

and it likes to sit at 13.5v at stoplights.

I have a digital voltage readout on my dash right above my rpm so im always looking at it.

some one told me that having two diffrent styles of battery is probably causing my alternator to see funny things in its charging mode, wich is why it could possibly be putting out lower voltages.

is this possibly true ?

and is there anything that I can do to fix this ?

I have heard about people adding some kind of in line resistor to the charge exite wire wich makes the alternator see a greater need for power ?

also saw some posts on that = a good way to start a fire in the car.

any how -

I do plan to get a good alt soon ( like 1 to 4 months from now )

but would like to make shure that all my issues are sorted by that time

so I dont do funny things to a $400+ alt.

lmk what yall think. thanks.

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[NoPh33rRaCiNg 10+ year member]

just kinda sounds like alt issue? i have no problems running a red top and kinetik in the rear.

 

[loopkiller 10+ year member]

Honestly OP it sounds like everything is fine, except that HC800 voltage seems a tad high. Now does your alt kick up to the higher voltage when you present a load? If not, it is supposed to kick down when it senses the batteries are full.

 

[brian84corvette 10+ year member]

no - once the alt is warm I guess, and it drops in voltage - it will not go back up.

even if I realley pump the system hard - and I start dropping in voltage down to 13.0 ish

when bassing out on something like dj billy e - the alt does not kick back in above 13.7.

for some reason I thought the alt should be making 14.4 all day long, at a lower amp when its not needed - but still keep 14.4 voltage. is this not a true statment ?

and running around at 13.7 is ok ? - I mean im not throwing my batterys on the charger or anything, and for the past fiew I have been beating up on my system - so if there was a big problem - then I would expect low voltage from my batterys - but they are both verry much charged up at the moment.

 

[dbeez 5,000+ posts]

Do you have a factory alt or high output alt installed..

 

[brian84corvette 10+ year member]

factory alt. was rated for 120a

but is old designed alt. I believe gm maxed out this crappy case alt and gave it the smallest pulley avalable to speed up alt rmp to give the most power it could at the time.

in 1985 they replaced this alt with a better unit. so 84 = ghey for me.

I have no idea if my alt in my car is the factory origonal, but I do know its old as heck

and should be replaced. im thinking what ever is inside it is not working like it used to.

haha.

 

[dbeez 5,000+ posts]

I would say 13.7 is not bad if the volts were really dropping then i would be concerned..

 

[loopkiller 10+ year member]

Overall, I would say that your voltages are by far safe, but they might not be optimal. Now I say this with the thinking of an SPL competitor in mind. If you were burping and needed that last 0.2db, then yes that half a volt would matter. But in a daily setup, if you don't drop below 13.0V and your batteries maintain a full charge, there is not much to worry about.