Testing a 404 dynamo

The Original Donk · Posted: Mon Oct 08, 2007 7:27 pm Post subject: Testing a 404 dynamo

After running the mog mainly backwards and forwards a matter of 5 metres i've not had much chance to try out the lighting, but today came that test when I was moving it about in the dark...when

The engine cut out and couldnt start it again from the drain from the batteries.

Ive got another two dynamos, so I want to know if there is a way of testing them?

failing that i suppose its more messing to make an alternator fit.

minimog · Off-Road Guru Joined: 25 Nov 2004 Odometer: 1700

dynamos workdiferently from alternators in that they only start to charge when they are turned a 1000-1500 rpm so if you have been running the mog on tickover or low revs it wont of even started to put any current into the batery so it will deaden the batery
you should have a light on the dash that stays lit untill the dynamo starts to work then it goes out
hope this helps

The Original Donk · Posted: Tue Oct 09, 2007 4:48 pm Post subject:

hmm, that may settle a bit easier beens as its a couple of days away from being roadworthy.

Im really looking forward to tarmac terrorising Twisted Evil

Ive not found a charge light for the dash yet so thats next on the list

DDBCretin · Gate Opener Joined: 29 Jul 2007 Odometer: 5

The charge light is the red lens over on the left hand side of the dash.

It should glow brightly when you turn the ignition on and dimly when the truck is idling. Like MiniMog said when you rev the engine up a bit the light should go out. The light is wired in such a way that it indicates the direction of current flow: If it's glowing then current is flowing out of the batteries. If it's not glowing then no battery current is being used or the batteries are being charged.

To test your generator rev the engine up a bit and check voltage between ground and the regulator positive terminal. If all is good it should read ~27-28 volts. Let the engine speed drop and it should fall to battery voltage ~24-25 volts.

An alternator upgrade is pretty easy and worthwhile. I installed a Delco 27SI a year ago and have had no trouble since doing so.

moggs · Posted: Wed Oct 10, 2007 1:48 pm Post subject: charging

silly question but you have wired up the dynamo correctly i presume ????
and another thing make sure the bulb works also as older wiring on things need the bulb to work, otherwise it wont charge
my alternator is off a leyland roadrunner 24 volt

The Original Donk · Posted: Thu Oct 11, 2007 8:25 am Post subject:

well i wired it up according to the wiring diagram you provided

but the bulb is not plugged into the holder

How easy is it to acquire and fit the alternator

I really want it running properly...its so close now.

Dave, did you get my text?

jackj · Gate Opener Joined: 11 Jun 2011 Odometer: 1

Can anyone help me by listing the steps involved in removing and replacing the dynamo on my 1937 4 1/4 ? Many thanks in advance.

dynamo laundry detergent

Turnip · Posted: Sat Jun 11, 2011 6:48 am Post subject:

On a standard 12 volt Lucas dynamo if you connect the F and D terminals together and put that to live of a battery then put earth to the body of the dynamo - it should run as a motor - obviously with the fan belt disconnected. If it doesnt, it is often down to brushes stuck in holders. Dynamos which have been left unused for a long period can lose their residual magnetism and need to be re polerised by "flashing" a live feed to the F terminal - motoring the dynamo to test it usually does this for you. I dont know how the terminals on a Mog dynamo are labelled and of course this is all at you own risk!!
Hope this helps?

Anyone want this nice complete 404 cab before I have to learn how to put it on "that site" ?