Another Alternator Question

So monitor my alternator output thru the Bluetooth connection on my Victron DC to DC charger shows my alternator voltage fluctuates between 12.4v and 13.7 and sometimes a bit higher. So my DC to DC charger will cycle on and off quite a bit due to low voltage. Pretty sure this is not a new problem, Verified by the voltage reading on my USB chargers. Varying rpm doesn’t seem to have an effect.
Could it be a faulty regulator or alternator or something else? How could I go about testing?
I’m not really a fan of crawling in beside the engine when it is running.
Standard equipment Motorola 55 amp alternator and voltage regulator on a Lehman 120.

How big is the dc to dc charger? Is it pulling so much current that the alternator can’t keep up, and drawing the voltage down on the battery till it drops out?

Bmarler said:

How big is the dc to dc charger? Is it pulling so much current that the alternator can’t keep up, and drawing the voltage down on the battery till it drops out?

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18amp

Ahh, sounds more like a regulator problem to me then. If there’s an alternator shop around I’d take it in and have it looked at.
I am assuming we are talking about an internally regulated alternator.

I believe the regulator can be replaced separately. I think alternator would be specified as the 8MR series. As for as I can tell the alternator number is 8MR2048K. The tag is a bit difficult to read. I think it is a 51 amp alternator.

If it was me, I would replace it with a bigger Alt. But like I said, thats me......

At 30 bucks it’s cheap to try.
Also agree that a bigger alternator with external regulation would be a nice upgrade.

Iggy said:

If it was me, I would replace it with a bigger Alt. But like I said, thats me......

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I'm not opposed to that if someone recommended a direct replacement unit. I have no need for a high dollar, high output, programmable alternator/regulator. We are not a power hungry boat.
But if all I need is a $30 regulator I'd go that route for now.

Anyone have source for the regulator?

The only regulator have come across yet are flat/flush on the backside. I need the regulator to have some space on the backside because there are a couple components on the alternator that come out beyond the housing, the current regulator is recessed on the back side to accommodate for this.

I am also still open to swapping the complete alternator for a plug n play unit,

I replaced the similar Motorola alts on my Perkins engines with rebuilt Delco 55 amp internally regulated marine alts I got at a local starter/alternator/battery shop. Not high output but simple one wire hookup and they do the job fine for me. They were about $150 each.

My thinking is correct that the alternator should always be putting out a constant voltage like 13.5 or more? and no reason for it to be fluctuating between 12.4 - 13.9?

Yes and no. Yes the alternator, if internally regulated, puts out a fixed voltage, typically 14.0 V +/- 0.5.

But if there is a fluctuating load, like an inverter powering a coffee pot, that heavy DC load will pull down the voltage from the alternator. So, in that case, no.

David

David is correct, voltage varies with load and also with the battery's state of charge.

If you want to have the alternator charge the battery significantly quicker, finding a regulator with a voltage set point of 14.4 volts rather than 13.8 volts will do the trick. At that voltage and provided you don't travel for days on end, an internal (2 stage) regulator will not hurt the battery and it provides just as much power as an external (3 stage) 14.4 V regulator.

Compass Marine (CMS on this site) may have something for you. Although I think the supply is limited. Here is a link.


If they are not available, maybe Rod will provide an alternative source.

I still have about 15 8MR conversion kits left..

I still have the original setup Motorola 8MR2018K alternator with the R7-1 regulator on the back of it. Just trying to find an economical solution to be sure it is working like it should be which I'm not sure it is. We don't have a high energy consumption on our boat and are just weekend warriors and a two week summer vacation.