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MG MGB Technical - Alternator that looks like a dynamo

Evening all,

Sorry to be so infrequent in posting in here. Having four young kids and my own business has never helped. My youngest starts Primary School in September, she's four, so hopefully I will have more time then.

Anyway, a quick question: I have a Mk1 MG BGT, standard other than running twin 12V batteries and a cutoff, fitted by the PO. I need a new alternator, and have seen some on eBay (gulp!) which look like dynamos. As I like an original look (recently ditched pancake filters for originals), I like the idea but thought I'd ask in here to see if anyone has ever tried one (and could maybe recommend a reputable supplier..?)

Thanks!

Piers
Piers Colver

Not on my PC at the moment, but I think I have a link to a website saved. I will have a look when I get a chance.
Dave O'Neill 2

Thank you Dave!
Piers Colver

Piers

Here are a couple...

http://www.powerlite-units.com/about-dynalites/

http://www.accuspark.co.uk/dynamator.htm
Dave O'Neill 2

That's very kind of you Dave, just what I was after (and much more reassuring than eBay..!). Thank you very much.
Piers Colver

Piers; curious about you using twin 12 volt batteries in tandum. By cutoff do you mean that they are only connected during use? In the electrical engineering world; keeping 12 volt lead acid batteries connected in tandum is taboo; because if one shorts, a fire could result due to rapid high current drain.
Rich Boris

I recently viewed a V8 which had 2x 12v batteries. I'm not keen on the idea, either.
Dave O'Neill 2

Fairly common practice on comercial vehicles to have two 12v batteries and a cutout to disconnect one when the ignition switch is in the off position
Having it wired like this is like carrying your own jumper battery with you all the time
If you happen to leave your lights on or run the battery flat somehow, as soon as you turn the key to on you have the other battery there ready to supply that power you need to start

willy
William Revit

How often do people flatten the battery by leaving the lights on, I wonder. Having had a couple of (Lucas!) batteries suddenly fail with no prior warning, it would have been useful in that circumstance. But even then it's only been twice in 40 years, not worth the weight or the outlay to me.
paulh4

Hi Rich,

Yes, two 12V batteries connected in tandem, installed in the wells under the back 'seat'. There is a cutoff in the rear footwell, operated using a red plastic key on the key fob, which I turn off whenever the engine is off.

The setup was installed by the previous owner. He is an engineer so I tended to trust it, perhaps foolishly - I confess I had not considered the fire risk, thanks for raising it. Other than that, the car is entirely standard, mechanically. I have not messed with the mechanical side at all, yet, as the car had some bodywork issues - it had later, and rusty, doors fitted, as well as rusty front wings. So I have sorted those bits out, then the gearbox went so I had to shell out for a 3 synchro non-OD rebuild, which ate the rest of the budget. I'm only now thinking about the mechanical side in any detail. I will be able to take it all more seriously from the New Year - I'll have a new double garage, space for a second classic and some tools, and all with all four kids in school (finally) I'll also have some time on my hands. I work mostly from home so between that and the new garage/workshop (having it built in the Spring) I have this dream of letting the cars become a larger part of my life.

But aside from my ramble, you raise a good point - do people think I should be junking one of the batteries?

Thanks for all the thoughts.

Piers
Piers Colver

As Willy said, multiple batteries are common on commercial vehicles. In fact, it was/is common on larger non-commercial vehicles like diesel pick up trucks. My older semi used 4 six volt batteries hooked up 2 in parallel and two in series to arrive at 12 volts. Trucks slightly newer than mine did similar, but with all 12 volt batteries. It is also common in marine application.

If you get a dead short on a hot line from a battery, it may well cause a fire, but I fail to see why multiple batteries makes this any more likely other than the addition of an extra battery cable. If it were my car, I would leave both in place. When time comes for a new battery, I would probably replace with only one, but that would be a financial decision rather than a safety consideration.

Charley
C R Huff

I am not sure that I understand what the problem is with a single 12 volt battery. If the battery looses charge from little use of the car, you could do the same thing that I have done with our TD (which is not driven much in the winter due to chemicals used to retard icing on the roads). My solution is a battery tender that is plugged in whenever the TD is parked in the garage. The battery tender will keep the battery fully charged without over charging as it alternatively discharges the battery a small amount, then recharges the battery to the optimum level, keeping the battery fresh all the time, while greatly extending the lifetime of the battery. Cheers - Dave
DW DuBois

The trouble with using a battery tender all the time is that it conceals the fact that the battery is losing capacity. Fine if the car will be unused for many weeks, but otherwise you could travel away from home one night and find it is too weak to start next morning. Like many things they have their uses, but are not a panacea.

There are other options like jump-starting with a battery pack that can be kept in a glovebox, or super-capacitors. However you would need to test both from time to time to check they are still OK, and the latter needs a donor car to be charged up from.

Two standard capacity batteries in parallel will generate double the current if there is a short in the wiring, but since one is more than enough to start a fire it's a moot point. What's more of an issue is that no two batteries are the same and one will always discharge into the other if left parked with them still paralleled, and if one of them loses a cell that current could be significant.

Personally I don't think any of them are worth the bother.
paulh4

Thank you very much for all the thoughts! I love how no two cars are ever quite the same, even if they're superficially barely altered from standard.
Piers Colver

This thread was discussed between 22/07/2017 and 26/07/2017

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