Battery Help!?

[Matt29]

First off, thanks in advance for taking the time to read the lengthy post below. This support that this board continues to provide never ceases to amaze me.
My goal is to remove the 40 years of "custom" electrical work/bird's nest on my 28 Bertram FBC. I started by reading Nigel Calder's Boatowner's Manual from front to back, taking notes along the way, and referencing the advice of this board. After that, I started listing my current and future loads on the boat in an attempt to determine the required battery capacity. I intended on adding up the estimated hours of use for each load to figure the Ah required for the house bank. During this process, I did not take into account the microwave and AC b/c I would only be running those loads with a generator. I also assumed that trim tabs, hyd steering pump, radar, and windlass would only be running when the engine alternators were providing power to the bus. All that said I still came up with what seems to be a ridiculous battery capacity. Adjusting hours of use for certain loads (GPS, fishfinder/sounder, LED spreader lights, fridge) I still come up with an Ah rating of anywhere from 68Ah - 100Ah. Using some Nigel's thumbrules for sizing, assuming a regular dischard of 30% of the battery and adding in a 20% fudge factor, this has got me at a capacity of anywhere from 275 Ah - 400Ah?! Where am I going wrong here? The major loads that I assumed were:
2.8 DC amps for fridge (6hrs for overnight or offshore)
(2) 24W LED Spreader lights (6hrs for overnight fishing)
32W GPS/fishfinder (4hrs)
30W sounder (4hrs)
Misc LED lighting loads (7Ah)
Misc house loads - washdown pumps, toilet, bilge pumps, radio (26Ah)

I read alot here about some of you redoing your elec distrib, and Bruce always seems to be voice of experience and common sense. Please let me know if I am completely out to lunch here with my sizing calcs. (2) 8D house batteries to support 400Ah seems like overkill on a distrib with modest amenities.
One other question was starting batteries. Right now, I've got (2) group 27 deep cycle wet cells to turn my 5.7L gassers. They don't seem to have a problem and I was wondering if there was a problem mixing wet cell starting batteries with AGM or gels house batteries.

Thanks again for your time and support. I look forward to the day that I get this project to a rendezvous to thank you all in person.

Matt

[IRGuy]

Matt...

A couple of weeks ago I submitted to the "Owner Tips" section of the Bertram 33 forum ( www.bertram33.com ) a writeup on the complete replacement of my battery and main electrical panel systems I installed on my boat. You can access it there, and since it is in Microsoft Word format you can download it if you want. My philosophy about battery power is that like sex, no matter how much you have, you always think a little more would be nice.

As far as using different types of batteries for starting and house power I suspect this is OK until you want to recharge your battery banks from a single 120 volt shore powered charger. My TrueCharge charger, and I suspect most other mfgrs, has a switch that must be set for the different types of batteries it is recharging, so it can't charge two types at the same time, although you could reset it manually each time. Each type of battery requires a slightly different charging profile, and to use the wrong profile will probably result is shortened battery life, or possibly worse.

If you want to talk drop me an email with a phone number and I'll call you.

Frank
IRGuy@aol.com

[gplume]

IR-Guy - Nice write up. Thanks for sharing.

Matt 29- I have also read Calders book cover to cover. The rule of thimb is 50% discahrge. Its true that when you recharge, you rarely bring the batteres all the way up during a quick recharge. ( especially with those wimpy sailboat alternators and anemic regulators.) That is where he gets his 30% usable capcacity. Now, the reality of the situation is that if you just sit on the hook and charge up after you've used 100Ahours you won't be able to put that last few amp howers in without letting it charge for a long time. But, if you use the boat, after your discharge, like go somehere, or come back from fishing, you most certainly will run long enough to bring your batteries right back up. A couple hour run for me, and I am backinto the + amp hours.
I have 2 8D's, one for starting (isolated from all house loads....runs only things that run while underway), and one for house loads. I have gone as long as 3 days (being a little miserly) without drawing down 100 Ahr (8D capcity 210-220Ahr,,,hence my limit of 100.) Note- Beer in a cooler..only food in the fridge. I rewired most everything. Left only what was in perfect shape. When I did, I installed a Link 20 so you can see exactly where you are on each battery. For alternators 2 Balmar 150 amp alternators with "smart" regulators, so they charge at max amperage longer using " the ideal charge cureve" (says who?)

I agree with IR Guy...bad idea to mix battery technologies. I do think it is possible to get an 8D house batteriy that has 275 Ahrs..(Rolls makes it).

Based on your math, assuming 8D's and your current draw, based on you calculations,(I didn't check your math.) I think you are ok, provided you run things for a while after ward.

Recomend if you want to watch it...buy the Link 20.
The alternators and regulators are bit overkill, but I don't have a generator, so I went topself on the charging system.

[Matt29]

Frank,
Excellent info and some pretty pics. Nice job, thank you. I will most likely send you a pm and look to get in touch with you this weekend. I am going through that battery spec data gathering now and going crazy. I appreciate your insight. Sounds like I will be leaning towards same type of battery for all banks.

Gplume,
Thanks for your input. The 50% discharge is a whole other ballgame now for battery capacity. The reality of it is that the numbers I calculated are conservative and not the norm. That being said, I would think I'm ok with using the 50%. Thanks for the putting it in perspective. I am looking to get a little Honda portable genny for some loads when the wife wants to cruise in comfort for a weekend, but also plan on upgrading the charger and alternators for that peace of mind.

Thanks again for your experience and insights. I will keep the post update with what transpires.

Thanks,
Matt

[Matt29]

Frank - I sent you an email. Thanks for your help.

Anyone use Golf Cart Batteries for house loads? I spoke with a gentleman at Rolls Battery of New England when I was looking to get more info on their 8D. This guy was telling me that the Rolls 8D's (221 or 275 Ah) are designed for about 1300 duty cycles (and cost around $600), and that the WorseMarine Brand (SeaVolt) 8D's are designed for around 300 duty cycles (about $300). All said, he recommended that I not purchase from him and buy 2 Exide 6V Golf Car Batteries locally. He went on to say that they are designed for about 700 duty cycles and are rugged enough for marine use. Exide has got a 245Ah golf car battery for about $140. The math indicates that I should be able to get 12V & 245 Ah in the same footprint and weight of an 8D for under $300. Anyone have any experience with this setup. Is it indeed too good to be true? It is referenced in Nigel Calder's book, and I recall Bruce mentioning this option some time ago. Perhaps he or someone else will chime in.

Thanks,
Matt

[gplume]

Matt-

Don't know who you talked to at Rolls, but sounds like a real "tool" to me.

I was made aware of the Rolls deep cycle 8D by this distributor, who is a distributor in the marine district of New Bedoford Ma, and a supplier to the comercial fishing fleet.
http://www.cebeckman.com/

Rolls 8D @ 275Ahr, was around $250.00-275.00 (+ or -) (I can't remebmer the exact number, but is was for sure less than 300.00)

Std Deka 8D @ 220 Ahr that I bought was about $170.00

Not sure where you are getting your prices from, but they seem way high.

As far as the golf cart solution.....don't have any experience with this one, so you will have to wait for someone else to chime in.

[Kevin]

Matt,
I am using golf cart batteries on my boat. I bought them from a buddy that is a dealer so I only paid about 100 bucks each. I do not know all the amp hours and so forth but I can check them out this week and give you the specs. What I can tell you is each one wieghs about 63 pounds and looks the size of group 27 battery. I can run a amped stereo and fridge all day without a problem. Those batteries run the bilge pumps, electronics, tabs, lights and so forth. I only charge them with shore power battery charger and have never run out of juice. I do have to add water once in a while. May not be the best way but it has worked great for me and the price was right. Let me know if you want pics of the batteries because I need to get some photos of my swithces anyways.