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Alternator size and amp rating


James Agg

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Hello Robin Hood hive mind! I’m out and about again enjoying the car in the improved weather since sorting my fuel tank issues and so inevitably, my mind turns to other things to sort and improvements to make.

 

I raised up my steering column last year to make a little more room for my knees. Unfortunately I have noticed since doing so that the shaft is in fact touching the alternator. This is obviously far from ideal. It’s only lightly touching and so it’s not at present interfering with my steering ability, but for longevity’s sake of both shaft and alternator, I don’t want it to be this way forever! My alternator belt doesn’t appear to be doing especially well either, and so I’m turning my attention to addressing all of these things. I’ve been looking at possibilities for installing a more compact alternator to replace the stock Sierra Mk1 alternator that I’m guessing is in there currently.

 

I’ve found a compact alternator on Car Builder Solutions that appears based on measurements to be a smaller diameter than the stock alternator, but it is only 40amps which to me sounds a little low. What are the thoughts on this? My car isn’t massively complex electronically but it does have a few bits and pieces that might be overly costly to a 40amp alternator. I have a heater, windscreen wipers and a Sony Bluetooth headunit. The car otherwise has normal things you’d expect such as lights, dashboard cluster etc and all that’s required to run a standard 2.0l pinto. My wife and I are thinking of installing heated seats from intatrim in the not too distant future and so there is the potential draw of that to consider too. My knowledge of how many amps I generally need and what kind of a downsize is just too low is somewhat limited, so any thoughts would be much appreciated! Enjoy the weather - looking forward to Malvern!

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When you say heater I take it to be a standard car heater where the waste head from the engine is transfered to the car through a small water radiator and a fan so 2 to 5 amps depending on fan speed.

Lighting 5 amps for each headlight bulb plus 2 amps for everything else less if you have LED bulbs. so 12A.

Everything else you mention less than 5A. total.

So before electrical heated seats 20 to 25A max.

Electrical heated seats are about 10A per seat though some have a higher initial setting for quick heatup but would only be at that setting for short times unless you live in siberia. 10A gives 120W try touching an old 100W bulb in your house after only a short time you get burnt.

So I recon that 40A just about does you at night on a cold rainy day.

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Have a look at this - https://www.ebay.co.uk/itm/143548367716

It's small, light and 50 Amps rated.  I've bought one of these to replace the standard Ford item on the Cobra.  I fitted something similar on the 2B's pinto which worked well.  Bear in mind that you'll have to modify the existing brackets to suit and may need to provide a +12V ignition feed to it if your original one doesn't have one.

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  • 4 weeks later...
On 5/20/2024 at 3:34 PM, Foz said:

Have a look at this - https://www.ebay.co.uk/itm/143548367716

It's small, light and 50 Amps rated.  I've bought one of these to replace the standard Ford item on the Cobra.  I fitted something similar on the 2B's pinto which worked well.  Bear in mind that you'll have to modify the existing brackets to suit and may need to provide a +12V ignition feed to it if your original one doesn't have one.

Hi Foz. I got this alternator, sorted a bracket and had a crack at wiring it up, and I think it’s not charging as when I run with lights on and heater running, my battery voltage drops to about 11.8 or even worse if at dual carriageway speeds. It settles back up to the early 12s when I come to a standstill and turn off lights and heater, and eventually the battery reaches 12.6 again, so I’m guessing the B+ is doing its thing, but I am for some reason not getting the correct amount of voltage kicking back which makes me think that the ignition feed to the alternator isn’t right somehow. Any ideas? I took the feed to the ignition terminal from the accessory terminal on the ignition barrel and put a fuse in that wire, which hasn’t blown and I’m getting a resistance reading from one end of the cable to the other, so I can only conclude that I’m not doing something right in how I’m connecting it up. What did you do?

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I have now fitted one of these to the cobra and it works a treat but I did initially find that the connector I was using was making an intermittent connection & needed a good shove in.

I've attached the details that I used so you can check your connections - these alternators don't work without the 12V to the ignition terminal and I'm guessing that may be your problem.  Can you connect a meter or test lamp to the ignition terminal on the alternator and make sure you've got 12V ?

Hope this helps,  Steve

Alternator.pdf

Edited by Foz
typo
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I've just had another thought - check you have a good ground connection from the body of the alternator to the negative of the battery.  If you've painted your bracket it might be acting as an insulator and not giving you a good connection to ground.

 

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7 hours ago, Foz said:

I have now fitted one of these to the cobra and it works a treat but I did initially find that the connector I was using was making an intermittent connection & needed a good shove in.

I've attached the details that I used so you can check your connections - these alternators don't work without the 12V to the ignition terminal and I'm guessing that may be your problem.  Can you connect a meter or test lamp to the ignition terminal on the alternator and make sure you've got 12V ?

Hope this helps,  Steve

Alternator.pdf 184.13 kB · 5 downloads

Thanks Foz. Yes, that’s one thing I’m yet to do and that is test to see if I’m getting 12v off the ignition barrel to the alternator. My multimeter should tell all!

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The earth is from alternator to bracket, and the top section of the bracket is as it was with the OEM alternator except reversed to allow for the mounting eyelets being in a different place to the original alternator. Did you need to sand back some of the alternator’s finish for a good earth at the mounting point? I haven’t done and maybe I need to? As far as I know, the ground is good…

 

Re the battery warning light, it’s from the original Ford Sierra clocks and it illuminates when the ignition is in position 1, then it goes out in position 2 as the other warning lights come on, and then it never makes an appearance when the car is started… It’s leading me to believe that the diagram that was on the listing for the alternator (same one that Foz posted) has the labellings of the spade connectors the wrong way round? 

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1 hour ago, James Agg said:

Re the battery warning light, it’s from the original Ford Sierra clocks and it illuminates when the ignition is in position 1, then it goes out in position 2 as the other warning lights come on, and then it never makes an appearance when the car is started… It’s leading me to believe that the diagram that was on the listing for the alternator (same one that Foz posted) has the labellings of the spade connectors the wrong way round? 

You could test the circuit by ignoring the ignition if you are unsure of the voltage etc. Simply make up 2 wires to go directly from the battery 1 with a bulb the other without & connect them directly to the alternator, then put the multimeter across the battery, start the car & watch the voltage, once you've done that you will know if that is working or not, then you can fault the ignition barrel (if required)

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Hi James, to answer your questions :-

I didn't have to clean the alternator itself but did clean up my bracket so that there was a good connection to the alternator body.

I've just double checked the connections on mine and it is definitely wired exactly as the details I posted this morning.  The 12V ignition supply is connected to the terminal nearest the main B+ connection.

Your warning light should come on when you turn on the ignition and stay on until the engine starts and the alternator starts working.

It does sound as if you might have a wiring issue - get that multimeter earning it's keep.

Good luck !

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