Perkins 4108 Alternator amps?

[Jeff Peterson]

In making out a power budget for a CD 36, I am trying to estimate recharge times...does anyone know what power an original alternator for a 4018 is likely to put into the batteries...2 105AH AGMs

Thanks

[Jim_B]

I don't know if mine is original to the 4108 but the specs say it puts out 90 amps.

[John Danicic]

Jim B:

The alternator that came with my Perkins 4-108 was a internally regulated Motorola that would put-out, (according to the Link 10 meter) about 30 amps. I can't say I ever saw it put out more then that.

I replaced it with an externally regulated Power Max 80 that is rated at 80 amps max. I saw it putting out 50 plus amps once when the batteries were down about 30% but mostly it is around 35 amps and below and will drop quickly. Mariah has 440 amp hours in one house bank from four, T105 6 volt golf cart batteries.

The amount of out-put depends on your engine's RPMs, battery's state of charge and what accessories you are running at the time like refrigeration, lights, fans or such. All this is taken into account by the regulator which in Mariah's case is a Max Charge which controls the alternators out-put. I am very satisfied with this system.

Here is a shot of the set up. The MaxCharge Regulator is mounted on the engine bulkhead aft, (and out of the picture).

[Maine Sail]

John,

That output seems a tad low for one of Ham's PowerMax alts rated at 80A. Hot I would expect 65+ amps.. Your bank should easily take more than that alt can give, in bulk, so acceptance should not be an issue.. I just installed one of Ham's alts yesterday with a Balmar MC-614 that was pumping out 117-125A for over 30 minutes and the alt was running at 195 degrees. The belt could not take it so I had to cut the field in "belt manager" with the regulator. It now maxes out at about 87A but will run there all day long and limit the belt dust... Owner did not want to splurge for a serpentine kit.

I would check your regulator and make sure you're not running in belt manager or small engine mode as that could be why your output seems a little low? Also T105's like a higher charge voltage anywhere in the 14.6V to 14.8V range for absorption is fine, and they will love it. Also you can check the field voltage at the regulator in bulk and you should see at least 10.5V+. In bulk you will often see the field voltage at 11.7V - 12.2V and about 5.2 -5.6A of field current.. You can just stick a DVM probe into the blue wire where it joins the plug and find clean "terminal" to check it.


Perkins engines came with different alts over the years so it is hard to guess what the boat has now. The stock alts will work but they don't perform as well when hot when compared to an alt specifically wound for higher performance. AGM's will really give the stock alt a work out or may even cook it. The 60A Hitachi I replaced yesterday had been cooked by a bank of Odyssey TPPL AGM batts because it was simply running at full output for waaaaaaay too long......

[John Danicic]

Main Sail…

Thanks for your advice.
The 50 plus amp reading that I recall may have been with lower RPMs or as it started tapering down. Not sure there.

I must say that I haven't really paid that much attention to the out-put immediately after starting the engine.
I shall take note of what the Link says right after I start her and she is running at cruising RPM's. It very possibly could be a higher value.

I will also check and see if indeed, I set the MaxCharge to "belt manager", which I very well might have, as well as follow your other excellent suggestions.

My voltage, when the batteries are down, registers in the mid to high 14 volts range with both the solar panels and or the alternator. I always thought that was a little high as the old Perkins engine volt meter reads over in the red zone with those numbers. Good to get your learned opinion on how much voltage a T105 can take. They seem in good shape, (knock on wood) for six year old batteries.

My four 40 watt solar panels really take care of the batteries so I am rarely down below -30 amp hours used on the Link even after three or four days at anchor running the fridge, inverter, fans and lights. A really cloudy day can send me down to -60 or so but one sunny day pops her right back into the teens.

I do like the new alternator and the fancy smart regulator for long motoring sessions which can happen on lake passages in mid summer. The Motorola tended to overcharge and constant vigilance on the battery water level was in order. Now I top up in the fall and spring. It all really works well for my cruising location and use.

[Matt Cawthorne]

Jeff,
With the stock alternator I used to get 30-40 amps when running the engine at reasonably high speed and the batteries were low. The output would start to drop soon after starting the engine. I ended up changing it to an externally regulated Balmar unit that seems to put out 60+ amps, even at relatively low speed. I can get more amps, but don't generally run the engine that hard. Once the bulk phase is done, the output drops. the drop is gradual if the batteries were low and the drop is nearly instantaneous if the batteries were nearly full.

Matt

[David van den Burgh]

Jim B:

John,

I don't want to hijack the thread, but what is that seacock for in the lower-left corner of the picture, just below the fuel filter? I'm guessing raw water intake. If so, Ariel's is located behind the engine, right next to the port cockpit drain seacock.

[John Danicic]

Dave:

That is correct. It is the engine's freshwater seacock in the open position. The cockpit drain through-hulls are aft of the engine. The starboard seacock in the engine compartment and the port one is in the cockpit locker next to the holding tank pump-out through-hull.