17 replies to this topic

[Lewiseasterbrook]

hi everyone!

 

i have a 1978 mini 998 and i have fitted a custom sound system in the boot and inside the car im running a sub with seprate amp and two 6x9s from another seprate amp and when i turn it right up my power protection light comes on for my amp that powers the sub and i still get a flat battery with the engine running and music on loud, im sure that its the fact my altinator isnt strong enough to cope with both the cars need of electric and the sound system.

 

i went on the MINISPORT web site and found a 70 AMP altinator the one i have on the car at the momment is a 45AMP all im really wanting to find out is if i fit the new more powerful altinator is that all i will have the replace? or will i need a bigger battery? if i do it could make things really tricky!!

 

any help would be great!!

 

cheers:)

[Captain Mainwaring]

Both would be ideal really. A big battery will give you some more time at idle when the alternator isn't knocking out it's full capacity.

[Willthewelder]

Big batteries last longer. They're not working at max capacity cranking over on a freezingt cold morning..

[Skortchio]

That's a 2 fold question.

 

If your lights dim / amp cuts out / etc. when the car is running and you're electrics are on then your alternator isn't providing enough power and you need a higher capacity one.

If you are using electrics when the engine is off for long periods with no chance of running the car, then you need a larger battery.

 

Both situations assume that the wiring is good and there's no earthing going on that shouldn't be and the alternator in good condition.

Having a hoofing great battery won't fix things if the problem is with the power generated by the alternator, it will only delay it.

 

If the alternator isn't keeping the battery charged in normal driving then either the battery is naff, the alternator is naff, there is a bad earth sucking the power away or the load placed upon it is too great.

 

TLDR:

Check for bad earths to start with, if nothing is amiss then your alternator isn't up to the job.

If you plan on listening to music with the engine off for long periods a larger capacity battery (ideally a deep cycle) will let you start the car afterwards

[HarrysMini]

I would say get both. A mate of mine has modified his battery box to fit a battery from a Land Rover. It works brilliantly. The higher power alternator will make sure your battery stays charged.

[Lewiseasterbrook]

True but because I have built the boot, to make room for a bigger battery I will have to take everything back out witch is a lot of work

[Lewiseasterbrook]

All wiring is good and the battery is fully charged as I trickle charged it last night if I had I more powerfull altinator at 70amps would it damage the battery I am using by overcharging

[Skortchio]

You don't need to modify your boot for a bigger battery, by any means.

There's a whole range of batteries that will fit just fine in the standard battery box and provide more than enough AH and CCA for all but competition needs.

 

096 is about the absolute largest that will fit without modifications, costs about the same as a mini standard one too.

 

 

But as the problem is with the engine running then it is more likely the cause is the wimpy 45amp alt.

A 70 won't damage your battery, electricity works by draw not push. :)

Edited by Skortchio, 08 June 2013 - 09:14 AM.

[Lewiseasterbrook]

Cheers Skortchio big help! I guess your running something similar to what I am?

[lrostoke]

You'll probably want to look at upgrading the wires from the alternator to the solenoid.

 

No point fitting a 70amp alternator if the wirings only designed to take 45amp.

[Skortchio]

Did mini ever change the ve+ and earth leads? I thought they were universal.

No worries Lewis, my car has a fair amount of electrics, aye.
Running a 90 amp alternator with 0 gauge power and earth cables.
But for a basic stereo with amp and maybe some spots a fresh alternator is more than enough.
:)

The alt to solenoid wire is dead short so you'll not fet much v drop. Assuming the wires are the same across the models of course

[lrostoke]

On a 78 if the solenoid is in the original place the wire from the alternator will need to run to the drivers side inner wing.

 

later models the solenoid moved to the top of the starter motor so that is a fairly short wire

[Skortchio]

Ahh, I bow to your knowledge on this one :)

Then yes, totally agree a 4 gauge wire will be a good call.

[74mini1000]

I will be rewiring mine within a few weeks, I am fiberglassing my dash right now. I am going to run 2 gauge for power and ground. Then it is going to get a couple small amps and speakers. I have found 120-160 amp alts online for reasonably cheap. If I upgrade to that, I should probably rewire the entire car right?

[Skortchio]

120amp + is some pretty serious ICE!

If you're running non competition levels I'd advise against going beyond 70 amps, remember a bigger alternator will pull power from the engine. If you're not using it you'll be gimping your performance as a result.

 

But no, you won't need to rewire the whole car. the electrics will only pull the currant they need, the alternator doesn't pump it about the car like water or gas, for example :)

 

Did the same myself just a week ago.