Can you help me to understand this explanation from CDI on my charging issue?

[Rstacy]

Let me start by saying that CDI is very quick to respond to email questions. I appreciate that.
I have a 1978 Merc 900 that is putting out about 20 volts. I bought a CDI regulator/rectifier to cure this but the motor started surging at WOT with the CDI unit.
I sent CDI a note explaining the problem. This is some of the reply.

> sounds like you may have more
> problems than just a high charging on the rectifier. First you need to look
> at what battery you have in the boat, if it has come from Wal-Mart or any
> other place like Advanced or Interstate, Autozone all of those batteries
> are maintenance free batteries with fill caps on them and they are made for
> cars & Trucks not outboard motors. The battery you need for this motor is a
> Deka part number DP24 and also i don't know what rectifier you got from us
> but i would get one of regulated rectifiers part number 193-5114 you will
> have to put on the bullet connectors to make it fit and only use one bolt
> to hold it on but it will work great.

OK. I may need a different battery. If it is the battery causing the high voltage and replacing the battery with a Deka battery will cure this, then why do I need the CDI unit?
I then asked why the engine was surging at WOT with the CDI unit and this is where he lost me.

> I'm so sorry that i didn't answer that question.
>The reason it wants to act that way is now that it's charging again and
>the battery has a link to the stator it can back
> feed the voltage back to the stator and the stator doen't like voltage coming
>back to it so it will sometimes get a miss at higher rpms cause the stator is
>trying to make a lot of voltage. Hope this helps you!

You lost me. Tell me again why my motor is surging at WOT with the CDI unit and runs fine with the stock unit.
BTW, the current battery is an Interstate deep cycle marine battery.

 

[flyingscott]

You probably have an unregulated charging system they use the battery as the regulator. Those systems do not like deep cycle or sealed maintenance free batteries. Unregulated charging systems will run higher voltage so they will cause the electrolyte to evaporate faster so you need to be able to refill them. Deep cycle batteries generally do not make good starting batteries and they generally need to be charged slower. I would stop using the CDI unit and continue to run the stock unit if it runs better with it, I would call CDI about that problem .

 

[Rstacy]

I would stop using the CDI unit and continue to run the stock unit if it runs better with it, I would call CDI about that problem .

Thank you for the battery explanation. I did remove the CDI unit and reinstalled the stock rectifier. I do not understand why my engine doesn't run properly on the CDI unit.
This explanation from CDI for that problem completely confused me.

> The reason it wants to act that way is now that it's charging again and
> the battery has a link to the stator it can back
> feed the voltage back to the stator and the stator doen't like voltage coming
> back to it so it will sometimes get a miss at higher rpms cause the stator is
> trying to make a lot of voltage. Hope this helps you!

 

[Chris1956]

The respondent at CDI does not understand your ignition system. He seems to be describing the interaction between charging and ignition power coils, like would be found on an ADI ignition. I also, did not think his explanation is correct, even for an ADI ignition.

The battery advice he gave you is bunk as well, IMO. Whereas maintenance free batteries can deplete their electrolyte under high charging systems, there is usually a way to refill them. Look under the decal for the fill plugs and fill them. In addition, your charging system only puts out a small amount of charging current. maybe 9A maximum at high PM. A decent battery (maintenance free or otherwise) can easily handle your average charging rate, for years without a refill of water.

I still think you have some resistance in your wiring harness or the motor is wired wrong. Do you know what the charging amperage is? Maybe it is time for an ammeter check to see what she charges.

Double check the quick-disconnect, as they are prone to high resistance, due to corrosion.

 

[Rstacy]

Thank you Chris.

 

[merc850]

I had 16+v going into a new maintenance-free battery so I installed a Mercury regulator, very simple to do; and now I get 13.5v constantly. Here's the wiring diagram for your motor if you want to check voltages etc. I also installed a CDI (company) trigger and the instructions said to not exceed 16v so this was another reason to lower the voltage.

 

[Rstacy]

Where did you break the wiring to install the regulator? Do you have a part number for the regulator?

 

[merc850]

Here's the procedure; there is enough room on the front cowl support to install it there - I don't know the part Nr. It is probably from a newer V6 motor.

 

[Rstacy]

Thank you!
Does anyone know what regulator that is?