Alternator/regulator/new AGM batteries

[stevep]

Hi all -- My A4 has the original alternator (35 amps, I believe) and internal regulator. I recently installed 3 new AGM batteries, 1 bank (single battery) for engine starting and the other bank (2 batteries, close to 300 amps) for DC house power. Is it reasonable to expect my alternator/reg combination to adequately charge these new AGM batteries? Should I go to a new 3 stage regulator, with or without a new higher output alternator? Thanks for any comments and advice.
Steve

[mgraham]

I was surprised that no one has posted a response. I have the same situation, 74 vintage A4, original alternator, and I am putting in two banks of group 27 agm batteries. but I will only have about 100 amph per bank. My concern is whether they will burn out the current alternator. Did you call tech support to see about the issue? Also, are the West marine AGM's ok, or is there something better. Have to do this week, flooded batteries are shot.

[Don Moyer]

I was also hoping one of our electrical experts would respond, as it's easy for me to get in over my head in electrical issues. Until more reasoned help arrives, here's my advice based on what I think I know from personal
experience:

1) I had 3 West Marine AGM group 27 batteries in our previous boat and was well satisfied.

2) I don't believe your original 35 amp alternator will necessarily burn up overnight simply because you install larger batteries (the regulator will tend to protect it). The issue is how much of a load you intend to place on your electrical system. Remember that whatever you take out, the alternator will ultimately have to put back in and if you take a lot out, a lower powered alternator will work harder to keep up with the demand, run hotter, and will probably enjoy a relatively shorter life.

3) Probably the most significant limitation to using your original 35 amp alternator (I presume you mean the original Motorola) is that it is biased to maintain only 13.5 volts instead of 14.2 volts which is now standard in more modern alternators. This difference in regulator biased voltage means that your batteries will never reach as high a maximum charge as they would with a new alternator biased to 14.2 volts.

Don

[stevep]

More info

Don, mgraham, and others. I spent part of yesterday at the Annapolis sailboat show talking with all the electrical experts I could locate, including Balmar, and the mfg of my agm batteries. Bottom line is that that my currrent alternator will be adequate IF I can bypass its internal regulator and install a modern external smart regulator. (The Balmar rep said that an alternator shop should be able to disable the internal reg.) Don, you were correct in citing the regulator as the system limitation. Basically, with the internal regulator set at 13.5 volts, it will be impossible to fully charge the new agm batteries, and at some point sulfation will begin to occur. This is not an emergency, however, because I can fully charge my batteries using shore power through my installed Xantrex Truecharge 20 charger and that will overcome the limitations of my alternator/regulator. But for extended time away from shore power, a new regulator will be required. Hope this helps.

[knitchie]

External "smart" regulator recommendations

I'm on a mooring and don't have access to AC to recharge by batteries. I'm finding that my alternator is not adequately recharging my batteries and want to add an external smart regulator. Balmar has several choices. I'm sure there are other choices. So, what products has our community used that they would recommend?

[msauntry]

Any external regulator will work fine. Final output depends on the type of battery you use. Some call for 14.2 volts, others for as much as 14.7.

However, your alternator is internally regulated so you can't add an external regulator until that changes... either take it to an alternator shop and see if they can convert it, or buy a new alternator that accepts external regulation and keep the old as a backup.

[stevep]

New alternator and regulator

The solution that seemed best for me was to purchase a new Balmar 85 amp alternator (series 7, I think) and a Balmar MC612 external "smart" regulator. The alternator fit exactly in the space vacated by the original alternator using the same size belt and the regulator (along with a temperature lead) was straight forward to install. Everything works as well as I had hoped. Balmar usually has a combo package for A4 replacement.Good luck