13 replies to this topic

[cal844]

hello again folks!! 

i'm going to be fitting a CB radio for the runs this season, so i'd ideally like to fit a 70 amp alternator, do i need to modify my wiring?!

[KernowCooper]

No need for a upgrade just for the CB Radio standard they are only 4w or a max of 12w for the new ones coming July

[HarrysMini]

Definitely no need for a 70 amp alternator if the only modification you've done is a CB radio.

[cal844]

sorry, should have stated that the car has smiths auxillary guages(oil pressure, clock and volt meter) and there is also an amp for the radio aswell, the car has just been starting lately(slow crank but still starts) due to lots of short journeys...

[Dan]

Well if you do make lots of short journeys then a higher output alternator could help it charge quicker after starting but only if the current one is limiting it. Nothing you have fitted really warrants having a high output unit (depending on what is fitted now, you haven't said what car it is) but if you really want one the only wiring you would need to improve would be the link from the alternator to the solenoid. A higher capacity battery and a good check over of the main cables and earths would probably be a better investment.

[cal844]

Its my 1993 1275 carb car... It is currently fitted with a 45 amp item.. I find that the heater is slow at 40 mph in 4th gear, I like my heat!! Lol

I've checked the wiring, its in great condition for the original wiring

Edited by cal844, 11 March 2014 - 08:19 PM.

[Stu1961]

Am I correct in thinking these bigger alternators are a drain on horsepower.

[Cooperman]

A more powerful alternator, when it is putting out the maximum it can will obviously take more engine power to run it, but it won't be charging so often as it will charge quicker so the total power consumed in running the electrical system will be the same.

However, the correct way to 'size' an alternator is to do a 'power loading chart'.

You add up the wattage of every single electrical item which could be switched on at any one time. This gives you a maximum total wattage. Divide that total wattage by 12 which will give the maximum amps ever needed and multiply by 1.2 to give a 20% reserve. That is the size of alternator you need. Any bigger is unnecessary.

If a lot of short journeys are undertaken make sure the battery is trickle-charged overnight every few days. Even a 70 Amp alternator will take a full half-an-hour to re-charge a low battery at normal running revs.

[cal844]

Thanks cooperman!is there a list of wattage figures for every switched item??

[Cooperman]

Each item has a specific wattage, but first you need to list EVERY electrical item.

For example, each headlight main beam will be 55 watts, unless you have fitted 100 w bulbs.

Then do you have spot, fog or driving lights? If you do add these

The sidelights are 5 watts each side, front & rear.  

Then add number plate light bulbs, instrument lights, heated rear screen, heater motor, radio/stereo, etc.

Come back on here with any item in your list of which you are not sure of the power required.

[cal844]

Well its usually (during winter)

 

Screen demist

Heater

Lights

Radio

Wipers

And occasional indications ;)

[Dan]

That's about 25A.

[jelboy89]

What is the wattage of the rear screen?

Jez

[Dan]

60 ish, depends how many tracks are broken! I've measured them at just under 5 amps.