AGM and Wet Cell Together

[Paul L]

Originally Posted by Hubec

Lifeline seems to discourage the regular use of equalization so I suspect it may also be harmful to the batteries. Maybe you can only do it so many times? I definitely plan to do it this summer while the boat's on the hard. Now I just have to figure out a way to feed a constant 15.5v to my batts for 8 hours !?

When I spoke to the Lifeline rep at the boat show about the reality of charging on a cruising boat and AGMs, his advice was to equalize the batteries once a month.

Paul L

[Rick]

An equalization cycle consists of a constant current source, NOT a constant voltage. The current is set to a value between 3% and 7% of the Amp-hour rating of the battery. The cycle is applied after the battery is so-called fully charged and has "rested" for close to 24 hours on float voltage.

The cycle is terminaed when the terminal voltage reaches a value between 16V and 17.X Volts depending upon temperature and battery type unless excess gassing first occurs.

The fact that some chargers and inverter/charger combinations offer a so-called equalization cycle is actually a compromise in offering a relative safe, yet low, terminal voltage without having the ability to operate in a constant-current mode. Keep in mind that these chargers are NOT giving you a true equalization cycle yet the offer is better than nothing.

AGM batteries can benefit from a true equalization cycle when necessary yet ALL lead-acid batteries require such a cycle less often if one applies a sufficiently high acceptance voltage when using a 3-step charger that allows settability of the acceptance voltage. This is why a MINIMUM acceptance voltage is 14.4 V @ 20 deg. C. When using lower voltages for deeply discharged batteries equalization will be necessary more often.

[SV Someday Came]

I think it is fair to say my thread has been hijacked. The majority of posts at this point are far afield from my original questions and it my clearly tongue in cheek reminder of the intent of my thread has fallen on deaf ears.

But ... thanks to those that stayed on topic and gave me information directly relevant to what I asked.

Michael

[Paul L]

Originally Posted by MV

I don't know the answers to those questions Michael. Maybe someone who has posted on the thread here could give #3 and #4 a shot? The posters here certainly seem knowledgeable!

Good luck!


Michael

Originally Posted by MV

3. I have a Perkins 4108. I am thinking of adding a Balmar alternator. Given the configuration above (3 battteries 2+1) would it be a good idea to use one?

4. I am going to add an inverter, but the installation will likely have to wait a few months ($ outlay). Does the inverter have to be installed at the same time?

#3, I am not clear how many amp hours the total bank is and what the current alternator size is. It doesn't sound like you have a very large bank, so a stock alternator will probably do you fine.
#4 No problem waiting on the inverter install, as long as you plan to use a separate inverter, i.e. not one combined with a charger.

Paul L

[SV Someday Came]

Thanks Paul!

Knowing I can wait on the inverter is a huge relief. The electrician wanted to do all at the same time, but the costs are really mounting.

Approximately what makes for a small, moderate, or large size battery bank? I originally posted this description: One battery is a AGM West Marine 810 MCA/ 580 CCA 92AH @ 200hr. The other battery is a Trojan wet cell 770 MCA / 630 CCA 79AH @ 5 hr.

Does that give enough information as what size bank I do have?

Thanks for your response -- I do appreciate it.

Michael

[Paul L]

Michael,
Not exactly sure how to interpret your numbers, but it looks like you have a small bank, <200AH????. If this is correct, then most standard alternators would be large enough to deal with it. If you plan to move up to larger bank, say 400AH, and you plan to use the engine for a lot of the charging, then you can consider a high output alternator.

Paul L

[Hud3]

Michael,

In order to decide how much battery capacity to install for your house bank, you need to do a little homework, namely making an inventory of things you have onboard, or plan to install, that use 12 V DC power, either directly, or through an inverter. Once you have an idea of how many amp-hours of energy you'll be using on a daily basis, you can size your battery bank. Normally, you don't want to draw batteries down beyond 50%, so if you figure on 125 AH per day, the house bank should be at least 250-300 AH. Three Group 27 AGMs would amount to 300 AH.

Since I have refrigeration on my boat, I have six Group 27 AGMs, or 600 AH capacity.

Here are some links to articles you might want to read. Also, there's a book called "Living on 12 Volts with Ample Power" that does a pretty good job of laying out all the parameters. The author has a commercial interest, but his logic is sound. I found it to be helpful when I was trying to figure out what to do electrically on my new boat.

Calculating Your Electrical Load - SailNet Community

BoatUS BoatTECH Guides: Electrical Systems

BoatUS BoatTECH Guides: Battery Chargers

BoatUS BoatTECH Guides: Inverters

files.meetup.com/247150/How%20to%20size%20a%20Battery%20Bank.doc