volt drop on amp

[hold em]

hey, have a problem on my brothers nissian safari which is 24v but dont think thats the problem, ran the amp power cable from the battery to the amp which is 12v to earth, and 12.4v or so when everything turned off, turn on the car so the headunit turns on, and the voltage drops down to 7v?? so i pulled out all the wires to the amp except the power and it goes back to 12v, start putting the wires back in while its going while watching the volt meter and as soon as i plug in the remote wires it drops it down to 7v, tryed and different amp which is less watts and it pulls it down to 4v?? and the voltage from the remote wire to earth is 12v, anyone have any idea whats going on? and the power cable is not to small, its a massive cable and was working perfectly in another car

[holdenboy]

So the car is 24v.....what do you have along the lines of a 24-12v converter for the amp?

Something like an amplifier will need 20-40A+ 24-12v converter depending on the amp.

[hold em]

na theres 2 batterys, there in series so one feeds into the other so one is 24v to earth other is 12v to earth if u get what im saying

[holdenboy]

No not really, i understand there is two batteries wired in series (2 x 12v batteries), but i would assume both batteries would read 24v?

Then theres the other way to go, which is the two batteries wired in parallel, which would give you 12v at both batteries, is the vehicle itself 24v? (like the starter motor, alternator?).

I assume you have a fuse near the battery on the amps' power cable? I would be double checking that, its a common cause of resistance, which i think sounds like the problem.

[StoneX]

See for what he means about batteries in series... Series batteries : DC CIRCUITS

First battery to ground will be 12v at positive, second battery in series to ground will be 24v at positive. Example uses 6v batteries but you get the idea.

Some automotive equipment (usually from trucks) requires 24v, so this is how they do it in a 12v vehicle.

[axemurderer101]

i would be checking your ground cables, also how old is the battery your running your power cable from? im an auto elec apprentice and have had batteries when load tested drop from 12v to almost 0v when adding even a little load.

[hold em]

heres a diagram i drew explaning what i mean, i guess ill check the resistance of the wire, you recken the volt drop is caused by the load from the amp?

[holdenboy]

Ahh, thanks StoneX.....didnt realise you could do it like that (shows how much experience i have with 24v vehicles )

Still, i'd be checking the fuse / fuseholder, connection to battery terminal and the earths at the battery and the amp. Could also be the battery itself as axemurderer101 suggested.

[hold em]

i would be checking your ground cables, also how old is the battery your running your power cable from? im an auto elec apprentice and have had batteries when load tested drop from 12v to almost 0v when adding even a little load.

batterys should be good, about 3yrs old and dos'nt struggle to start or anything

[hold em]

all fixed, was a bad join to the battery, took it off gave it a sand a rejoined and fixed =)