hey peeps, me again, come to pick your brains in regards to my slovak warhorse problems...

basically ive narrowed down the charging problem to the alternator, more specifically the rotor, which is not magnetising as it should and therefore not generating the nescessary current to charge the battery...

as i understand it the alternator rotor is not a permanent magnet, but it is an electromagnet which is magnetised using the vehicles battery, and this sems to be where my alternator is failing.

now the question...

Is it possible to run a cable directly from the battery to the alternator rotor to manually excite it so i can check for an output?

of coarse, i could be talking complete bollocks, but any help would be appreciated as this is the only major problem that is stopping the jawa from being roadworthy...

Here's the schematic if it helps:

am i right in thinking that the field current ("DF" in the schematic) is supplied from the regulator?, if so then is it possible that the regulator is at fault? (is there any way to test it)

Here's the schematic if it helps:

am i right in thinking that the field current ("DF" in the schematic) is supplied from the regulator?, if so then is it possible that the regulator is at fault? (is there any way to test it)

As to testing it God knows, i'm sure you can its just how. Looking at the drw'g i'd say the regulator controls the primary voltage and as such the magnetism in the armature to control the output voltage to acceptable levels.

In theory if you put a voltage across DF and run the motor it should charge then all you need is a way to control said output.

Have you already tested for continiuty across the rotor Steve ?

thanks for the reply cynic, but for the purpose of testing would i need to control the primary current to DF or would it be okay to just run a cable from the positive on the battery directly to the DF terminal on the alternator and see if the battery charges? (the engine would be idling so the output should be low enough to not do any damage if unregulated... in theory), if i then get a charge i will know its the regulator that is wanked out

another question, is the Rotor itself permanently magnetised? i may be able to buy a second hand rotor but i dont want it to de-magnetise in the post...

thanks for the reply cynic, but for the purpose of testing would i need to control the primary current to DF or would it be okay to just run a cable from the positive on the battery directly to the DF terminal on the alternator and see if the battery charges? (the engine would be idling so the output should be low enough to not do any damage if unregulated... in theory), if i then get a charge i will know its the regulator that is wanked out

another question, is the Rotor itself permanently magnetised? i may be able to buy a second hand rotor but i dont want it to de-magnetise in the post...

Can't see why it shouldnt generate something.

As to magnetism on the rotor i cannot say but the fact it has a coil winding in it suggests its not a permanant magnet as there are some magnetic contacts on there by the looks of it.

As said by barkwindjammer, you have done the basics and checked the continuity of all this. Especially as there will be a couple of sliprings/armature and some bushes somewhere in there. All weak spots.

BWJ: yes i tested for continuity and the reading was 0.3ohms which seems to be fine

The rotor isnt magnetised, its purely an electro-magnet made of soft iron (this doesnt mean it wont be slightly magnetised-with age), you can put 12v directly to the rotor circuit, this excites the rotor, once the alternator is spinning and powers up-this initial 12v kick drops off

not a bike alternator I kno', but they all work on same principal.

how it works

nice, i'll give it a spark off the battery tomorrow and see if that will get a charge... if that works then i will try swapping out the regulator... (no doubt another part made from unobtanium)

the voltage regulator controls the amount of juice to the electromagnet which then controls the amount of charging that occurrs.

this is to stop the battery overcharging. I'd look there!

drewps

According to the workshop manual, there is no way to test the regulator under workshop conditions...

if i can find a regulator with the same connections will it be a straight fit or does it need to be any particular specification? (Wattage, Amps, Ohms, Lightyears e.t.c)

Would THIS fit?

tried sparking the field current directly from the battery with a multimeter measuring the voltage across the battery but there was no voltage increase in the battery and thus no charge... so i moved the multimeter to the negative side of the rotor but was getting about 0.2 vdc...

so, does that mean the rotor is f*cked?

If your getting a continuity reading then the rotor is ok, its only 1 single winding, therefore you get something or nothing usually, however you shouldnt get a continuity reading between winding and any other metal parts of the rotor-except obviously the commutator, normally as well as the insulating varnish layer there will be a plastic shield that the coil is wrapped around, so it seems unlikely that there would be a 'short' from the coil to the rotor shaft

tested the rotor winding and have continuity between the two terminals but no continuity to the casing or rotor shaft...

negotiations for a second hand rotor have begun...

tested the rotor winding and have continuity between the two terminals but no continuity to the casing or rotor shaft...

negotiations for a second hand rotor have begun...

sup to you m8, but I'd go wi Drewpy and say the problem sounds like its in the regulator/rectifier area

i cant really see how that would be, ive tested the diode bank/rectifier and they are all functioning correctly, and i bypassed the regulator when i applied the field current... :S

sods law really, when i've got the time to play with it i havent got the money, and when ive got the money i dont have the time! , will have to wait until im in work now as replacing both the regulator and rotor is out of the question, its going to have to be one or the other

new alternator rotor has been sourced and ordered, £13 inc p&p