Modding an Iskra 100 Amp Alternator

London, ON

The procedure in this blog worked for me.  I do not guarantee it will work for you and if you attempt the mod yourself good for you but you are on your own.  You are responsible for any damage you incur.  Don't be stupid.  I do not know much about alternators or diesels and if you do what I suggest it is a case of the blind being lead by the blinder.  I have no expertise.  This is just something that worked for me.  It may not work for you.

Here you see the alternator in its native environment.
Note the rugged construction - and the 5 Groove serpentine Belt

When we ordered our new Beta 43 diesel a couple of years ago we fitted a 100 amp alternator built by Iskra, a company out of Slovenia equipped with a 5 groove serpentine belt.  With only one exception we were totally satisfied.


Unfortunately the Beta supplied Iskra is regulated by an N type internal single stage regulator.   Most boats in North America use three stage external regulators to drive their higher output  alternators.  

• The benefits of multi stage regulation are discussed by Don Casey in a decent online article at www.sailnet.com/forums/miscellaneous/22175-understanding-three-stage-regulator.html.  

We modified our Iskra alternator and it is now uses P type externally regulated three stage regulation.  It was a simple modification.  Here's how:


What you Need:

1. Iskra brush holder available from Beta marine for a reasonable $40,
2. 5/16" combination wrench and, if you have it, a 5/16" socket,
3. 1/2" open end wrench,
4. a small phillips head screwdriver,
5. a pair of sidecutters or a sharp knife.

The Procedures Step by Step:

1. Turn off the DC power (shut off the main switch),
2. Remove the alternator from the engine and remove the three existing wires,
3. Remove the back cover from the alternator (3 nuts),
4. Remove the internal regulator (2 nuts and one screw),
5. Install the brush holder (2 nuts),
6. Cut an access hole in the back cover for the wires to the brush holder,
7. Run the wires from the brush holder through the access hole,
8. Gently replace the rear cover (3 nuts),
9. Wire up the external regulator,
10. Return the alternator to the engine and reconnect the three wires,
11. Restore DC power

In Pictures:

The alternator sits calmly unaware of what is about to happen.

There will be three wires on the back of the alternator.  Depending on what is easier you can remove the wires and then the alternator or remove the alternator and then the wires.


Often the wires are short. If you remove the alternator before the wires you may rip the wires out by accident.  Just go slow and be gentle.

Removing the big wire from the back of the alternator using the 1/2" open end wrench.  


The big wire is positive and is connected through the battery switch directly to the battery.  If you short it to the engine block you will get a lot of sparks and some melted metal.  Avoid this.


I wrap all tools in electrical tape when working around wiring on the engine.

In an excess of caution I wrap the exposed end of the big wire with electrical tape to prevent accidental shorts.


Once I did not wrap the end and I got lots of sparks and some melted wire.  This is how I learned to avoid this.



 Here is the alternator removed from the engine.  It is resting face down (the pulley is on the blue mat) and you are looking at the back.


I have drawn orange circles around the three nuts you must remove to take off the rear cover.  One of the nuts is recessed and if you have a 5/16" socket it makes life easier.

Shown here is a lug on the back of the alternator which is held in place by another 5/16" nut.  You only need to remove the top nut and the tab.  Do not remove the nut which you will find under the tab.  Not fatal if you do but why cause yourself more work.


When you have removed the tab just gently pull the rear cover straight off the alternator. GENTLY.  You do not need to worry about brushes or anything.  Just gently pull the cover straight off.

When the cover is removed this is what you will see.  


Cool.

The photo to the right shows the internal regulator.

Here you see the regulator from a different angle.  Circled are the two nuts and the one screw you must take off to remove the internal regulator.

Just remove the nuts and the screw and then gently lift the regulator off the posts on which it is braced.  Be careful because you are removing the brushes too which are an integral part of the regulator assembly.

Removing the nuts on the internal regulator assembly.

Removing the single screw on the internal regulator assembly.

Installing the new brush holder.

You have to place the brush holder on the two posts which held the regulator assembly, depress the two brushes and gently lower the assembly and brushes into place.  

This is not hard but it is fiddly.  The brushes rub on the rotor and can jam.  The brushes are fragile.  Being gentle will pay huge dividends.

If you have trouble getting the brushes to go on the rotor wrap some heavy paper around the rotor and press the brushes against the paper.  


You can then press the brushes against the paper and easily lower the brush holder on its posts.  When you have the brush holder in place just slide the paper off the rotor.  Easy peasy.

Here you see the brush holder sitting nicely in place where the regulator used to sit.


You now have to replace the two nuts on the posts holding the brush holder.  


You can see the wires coming off the holder.  

You can see the wires coming off the brush holder.  You must lead these wires outside the rear case.  


To do this cut off a hole in the ventilated part of the rear cover.  Just cut off one of the plastic bits.  Leading the wire harness through the resulting hole is tight but doable.  Why have a bigger hole than you need.

The hole is made.  


Lead the wire harness out the hole and gently replace the rear cover.  This cover will only go on the rotor one way.  Look closely at the inside of the rear cover and this will be immediately obvious.


If it isn't find someone with an IQ of 65 or higher and ask for help.  If your dog is smart he may be able to assist.

The rewired alternator. A lot more connections but all
due to the external regulator.

Replace the nuts you took off the rear cover and put the tab back on.  


You can see the wire harness leading out of the back of the rear cover.


Now it is time to rewire the alternator.


This is remarkably easy.


You put back the three wires you took off in the first place: the big positive wire, the tach wire and the voltage sense wire.


Then you have to follow your regulator instructions for wiring.  Usually these were written by a Taiwanese teenager with a serious crack habit and a passing acquaintance with the English language.  Oh well.  You are on your own except for this:


You will have to connect two wires to the wiring harness.  One is a negative wire and you can take the negative wire off any DC ground. I use the "neg" post on the alternator itself.  The other wire to the wire harness is "stator" and it will come from the regulator.


Here is the joyous bit: IT DOES NOT MATTER WHICH WIRE YOU CONNECT TO WHICH.  There are two connections in the wiring harness.  One is negative and the other is stator.  It does not matter which is which.  Cool.


You are done.  Reinstall the altenator and start the diesel.  If nothing burns up you are golden.

Here is the brush holder.  You will see immediately