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A tired out alternator is a chance for a "power upgrade"...
New Alternator for 1988 Hull #849 – S/V "Dutch Boy"
by Hans Treu
My 1988 C-36 was equipped with a standard Motorola 50 Amps alternator and a manually controlled "Spa Creek" voltage regulator.
Recently this voltage regulator quit working and even with this equipment turned off, my batteries were not charging properly by the alternator. When still working, the manual voltage regulator had to be used very carefully to ensure it would not overcharge the batteries. I did that a few times when I forgot to re-adjust it in time. So I decided to install a new larger alternator and a "smart" and automatic voltage regulator.
I reviewed Rodd Collins’ (owner of S/V Hale Kai) article on his 100A alternator upgrade and I did take a close look at the Leece-Neville 70A (8MR2058KA) and 90A (8MR2069TA) alternators. I did not want to install a heavier belt system, nor did I want to upgrade the alternator output too much in order to maintain maximum power for propulsion. So I decided to upgrade to no more than 70-75 Amps. My house bank consists of two 6-Volt Trojan 105 batteries (225AH) and I have a separate Interstate size 24 starting battery charged through a West Marine combiner.
I contacted Balmar® in Arlington, WA, to find out which of their alternator types might be most suitable for my 1987 Universal M25-XP engine, without requiring a complete rebuilt of the alternator bracket. I ended up e-mailing with Rick Jones - Balmar Market Development, at rjones@balmar.net. Rick suggested that I use their 812-65A alternator and their ARS-5 regulator.
This chart serves as the alternator spec sheet. The 812 series alternators are not sold by the usual marine stores and discount houses, so Balmar sold me the alternator and the ARS-5 regulator directly for a reasonable price. Essentially the Balmar Series 812 alternators use the same "frame" as the Leece-Neville alternators 8MR series alternators, so the housing is virtually the same as my Motorola 50A MR8 alternator. Actually when I received the Balmar 812-65 alternator the label shows it was built by Leece-Neville, but it has a separate ground and insulated housing, it is set up for external voltage regulation out off the box, and may have larger bearings than the Leece Neville MR8 units, since the pulley shaft is 17mm instead of 5/8" (15.88mm).
I had hoped that I could just remove the Motorola unit and replace it with the Balmar 812-65 alternator, but the larger diameter cooling fan on the Balmar unit interfered with the alternator tensioning arm. The Motorola fan has a diameter of 127mm (5inch), while the Balmar 812 unit has a 134mm diameter fan. The Balmar V-belt pulley diameter was also slightly smaller when using a 3/8" belt, requiring a shorter belt or more alternator offset to tension the existing belt. Otherwise the unit fit the housing well, but I had to make some changes to make the unit fit.
I decided to re-use the existing Motorola fan but since the fan blades are much deeper I needed a 3mm thick spacer ring to keep the Motorola fan blades clear off the housing. See the next photo...
This photo shows the "too large" Balmar fan, the modified and repainted Motorola fan (now with 17mm shaft bore), the 3mm thick spacer ring that goes inside of the Motorola fan, and the original Motorola pulley. I had the inside face of this original pulley machined down ~2mm to get proper belt alignment and to give the shaft nut ample thread on the shaft. This machining work cost $45 at a local machine shop.
Here, with the Balmar 812-65 alternator assembled on the engine, you can see that the clearance between the tensioning arm and original Motorola fan is only 2mm -- which is why the new Balmar alternator fan would not fit. By the way, it was not easy to get the fan and pulley off the old Motorola alternator, since the nut would not budge. I had to cut the nut in two using a Dremel tool.
The new alternator is now fully installed...
...and in its first test run.
I installed the new Balmar ARS-5 voltage regulator in bulkhead beneath the companionway in the same place as the original manual regulator unit, but facing into the aft cabin instead to keep it free of water spray or rain water coming into the companionway opening.
Here is the ARS-5, fully installed.
I will add a battery temperature sensor wire later as suggested by Balmar®. Balmar® seems less concerned about overheating this alternator, since they consider it over-designed (or under utilized). I will also add a separate Ammeter later to monitor charging Amps. I already have digital voltmeters for both battery banks so I can monitor battery voltage quite well.
The new alternator and voltage regulator appear to be working well, and I feel that it provides adequate charging for my battery systems and DC power use while underway, and the alternator does not appear to get too hot even here in Texas. Total costs for this upgrade was about $530 including shipping and machining work.
by Hans Treu
Hull 849
Sealy, Texas