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MG TD TF 1500 - Low cost alterrnator in a dynamo case

Here is a comparison of the std C39 PV2 dynamo from a TF and the low cost alternator (costs 139.95 with Tacho drive in the UK). The alternator is slightly wider. The old pulley wheel and fan drop straight on to the shaft and woodruff key. The spring washer provided is too thick to get the nut more than half on, so I substituted with a thinner plain washer. The main terminal in a 9.5mm male blade. The minor terminal is a std blade, but there is also provision for an M4 nut. The std mountings are correctly spaced. There is no lubricator for the rear bearing and as a consequence the threaded extension for the tacho projects less. The std tacho reduction gearbox fixes straight on. This gives rather more clearance between the gearbox and the distributor, which to my mind is a very good thing, especially if like me you have a non std (larger diameter) distributor. The vent holes at the front of the alternator are clearly larger than on the dynamo. Construction externally is all alloy castings. It is advised that the cable link from the alternator to the battery is upgraded to 45Amp. The instructions are very brief but there are circuit diagrams for rewiring using the existing voltage regulator (taking its functionality out of circuit), or for using a dummy regulator. The dummy regulators seem overpriced so my plan is convert a scrap regulator into a dummy, and use the internal space for an in-line fuse. More when all up and running.

Dave Hill

Hi Dave,

Fitting fuses inside the old regulator is an easy job - see attached photo. Please let us know how your alternator performs. The one I had problems with was different to yours and vastly more expensive c400. I fitted heavy duty wiring and was concerned about the ammeter - my alternator is rated at 75A. However all appears to be fine. After starting the engine and switching everything on - halogen lamps, auxiliary lamps, electric fan etc. the meter shows a 5A charge but this quickly goes down to just over zero. I suspect the problem could be if I had a fully discharged battery when 75A would be available for charging!

Jan T

J Targosz

Good stuff. Interesting, your choice of fuse, I was just going to use a single 40Amp blade type, this being the max for that type. The max output of the alternator is said to be 45Amp, which is easily enough for me. What you are experiencing with the ammeter is much in line with my expectations - should be fine as long as the battery doesn't get very run down. I was thinking the simplest method to upgrade tye wiring would be to double up between the alternator and the ammeter, and the ammeter and the battery.
Dave H
Dave Hill


That looks great, but what alternator is it?

I would like to try it on my TF, but who sells it?
Don Harmer

Hi Dave,

Try Vehicle Wiring Products they have everything you could possibly need and their catalogue has details of the current capacity of all the wire they sell. I had several old fuse boxes and I was able to cannibalise the clips for my conversion. I have fitted relays for all the lamps and the electric fan and took a heavy duty wire from the alternator to my "fuse box" and then on to the power contacts on the relays. I used the original lamp switches and wiring to power the relay coils. I had considered connecting the heavy duty wire to the battery to disable the discharging side of the ammeter but it is the charging which is critical. I used "thin wall" cables which are similar diameter to the originals but can take about three times the current. Vehicle Wiring Products have all the original core colours and tracers. I wrapped my loom with "Tessa Tape" and you will see from the photo of my fuses it looks very good.


J Targosz

Ok, will do. I used relays on the headlights and thermostatic fan as well. Had considered doing so on the foglights, but not bothered because I'll probably never use them, and may switch to LEDs anyway. Also considering a relay on the brake lights to save the pressure switch - I have had a couple of attempts to buy suitable LEDs instead, but they turn out to be either too short to be visible from the side or the dual functionality with the side lights is not operational for some reason that I can't fathom.

These cheap alternators are sold in the UK by BB Classics and Accuspark. Somebody will be selling them in the US. At the price I paid they must be being made in the Far East or India. Having said that, they look quite well made.
Dave H

Dave Hill

This thread was discussed on 02/03/2015

MG TD TF 1500 index

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