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MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG TD TF 1500 - Dynolite and Dynomator Alternators

I know the issue of alternator conversions was featured quite recently but I was at MG Live at Silverstone yesterday and was able to examine both a Dynalite and Dynamator alternator conversion. The former is expensive at £500 but is metal bodied and has a tacho take off. It appeared to be a little bigger in diameter than an original but the length was the same. The latter is much cheaper at £140 but doesn't have the tacho drive and the main casing appeared to be plastic with aluminium end plates. Before I commit to buying one, probably the Dynalite so I can use the tacho, I would love to hear the experiences from someone who has actually done a conversion. I have mentioned before that I tried to fit an alternator from a Ford Transit to my TF but there wasn't room within the tapering bonnet. One excellent tip I picked up though is to connect the output from the alternator, with a new 60A wire, directly to the battery side of the starter switch and then a wire from this connection to feed the car's electrical circuits. This means the ammeter will only show a discharge but won't be fried if the alternator is charging a run down battery.


Jan T
J Targosz

Jan,

I was told by a good source that the ammeters are overbuilt and can take far more than 30 amps - basically not to worry about it.


Jim
J Barry

Jan,

I cannot attest to the strength of the amp meter in a T series but I have converted a good number of other machines over the years and although the amp meters peg for a few seconds after start they seem to shrug it off. I believe Jim Barry is correct in that they're overbuilt enough to take it.

Jim
JE Carroll

How do you isolate the battery power to alternator when engine is off if connected directly?
Don
D Hanna

Don, it's just a swag, but diodes in the alternator would handle the isolation. I believe that the alternator requires that a voltage must be applied to the control terminal for anything to happen. Bud
Bud Krueger

Don,

Bud is correct; the diodes take care of isolation. The battery terminal on an alternator is always hot. Unlike a generator, never disconnect an alternator from the battery, or disconnect the battery in an alternator equipped car if the engine is running as it usually results in alternator destruction. It's usually not a problem but many T cars have a battery disconnect switch which is an alternator killer if so equipped and switched while running.


Jim
JE Carroll

Hi Jim,

I have a killer switch on the earth lead of the battery. This isolates everything (including the clock!). I have never switched this off with the engine running but if I did, and had fitted an alternator, would this destroy the alternator?

Jan T
J Targosz

Jan,

Here's something of an explanation from a marine battery switch installation guide:

If a battery switch is turned off while the alternator is producing current, the voltage will increase due to the sudden elimination of the load. This will burn the diodes out in the rectifier quickly. To prevent this, a battery switch with an alternator field disconnect (AFD) can be used. The AFD is a secondary, isolated, single pole switch within the battery switch, through which the alternator field current source wire from the voltage regulator is wired.

The AFD is constructed in such a way that the AFD switch does not close until slightly after the main switch contacts have closed and it opens slightly before the main switch contacts open. This insures that there will always be a path for the alternator's output current when the alternator is producing power. The field disconnect will only work on alternators with an external regulator. The diagram below illustrates the connections. Blue Sea Systems battery switches 9002 and 9004 have an AFD.

I've managed to kill three myself. No, I'm not a slow learner as two were by accident.

The first was about 45 years ago. It was common to disconnect a battery to see if the generator was working and a volt meter wasn't handy. I tried it on a new alternator equipped car. The lights went way bright then died as the alternator gave up. The next was when I shut the battery switch off on a loader as one of the headlight wires had smoke escaping. I stopped the fire but the alternator was toast too. The last was when I was standing on the door ledge of a truck reaching for the roof lights to replace a bulb and kicked the battery disconnect while doing it. Again the lights went real bright then died.

I've read that the alternator may just spike but continue to work but I've killed three and marine shutoff switches are available that disconnect the field before interrupting the main power. So I wouldn't chance it.

Jim
JE Carroll

Thanks for explaining the need for power to the alternator. My MGs all have generators and battery shut offs. I am thinking of changing the TD to an alternator, the engine and the rest of the drive line is MGA so there is no need to worry about keeping it stock. I had just assumed that when the key was off the alternator was disconnected.
I learn something everyday here, wish I could retain it all.
Don
D Hanna

This thread was discussed between 22/06/2014 and 24/06/2014

MG TD TF 1500 index

This thread is from the archive. The Live MG TD TF 1500 BBS is active now.