The battery choice can be difficult. Here's some general information that is generally accepted on this board.
FLA (flooded lead acid) batteries are typically run to about a 60% DoD (depth of discharge). Some people go deeper, but many consider this depth to be a good compromise between energy delivered and maintaining a long life, measured in charge cycles.
AGM (absorbed glass mat) batteries can be discharged to the 70-80% range. I generally consider a 70% discharge for AGM systems.
There is a trait called the Peukert Effect, this describes a battery's decreased ability to deliver energy at higher amp loads. Jim's post touched on this. I won't go into the math here, but that loss is predictable through Peukert's equations.
FLA batteries are usually more affected by Peukerts Effect than AGM batteries.
All of that said, here's a quick calculation of your range of both of your proposed battery banks at a 2kW load (42A @ 48V). That should drive your boat to somewhere between 4 and 5kts, your results will vary.
(4) Trojan T1275 - 150Ah @ 48V, Peukert exponent = 1.2
Time to 60% DoD = 91 minutes
(4) Odyssey PC2150 - 100Ah @48V, Peukert exponent = 1.1
Time to 75% DoD = 86.5 minutes
The PC2150s are a little smaller and lighter and they won't need maintenance. I typically recommend AGM as a good balance of price and performance. Like Mike said, you will need a charger that has an AGM charging profile, a regular FLA charger will kill your AGM batteries in a small number of charging cycles. Picking the right charger is not generally a problem, but worth paying attention to.
The calcs also show why many mid size sailboats conversions aim for battery banks that are somewhere between 200 and 300Ah. Larger banks also reduce the Peukert Effect so there is not as much range lost to the 2kW load.
Fair winds,
Eric
Marina del Rey, CA
--- In electricboats@yahoogroups.com, "luv2bsailin" <luv2bsailin@...> wrote:
>
> What are your speed and range needs? Those 20 hour AH numbers don't mean much at the higher draws. I found that Trojan battery you mentioned on their site. Duration at 56A was listed as around 100 minutes. I assume that is a deep discharge. You wouldn't want to run that size battery continuously at much over 50A. I would go bigger unless you just need to tool around for an hour at 5 kt or so.
> Jim
>
> > ________________________________
> > From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com] On Behalf Of Capt. Mike
> > Sent: Tuesday, September 28, 2010 3:11 PM
> > To: ELECTRIC BOAT GROUP
> > Subject: Re: [Electric Boats] Re: Catalina Conversion
> >
> > AGM makes your life easier IMO. Plus no more acid burns in your clothes. Just make sure you spec your charger to tje type of battery you are installing.
> >
> > Capt. Mike
> >
> > Sent from on board BIANKA
> > http://biankablog.blogspot.com
> >
> > ________________________________
> > From: "Doug" <dj2210@>
> > Sender: electricboats@yahoogroups.com
> > Date: Tue, 28 Sep 2010 18:09:31 +0000
> > To: <electricboats@yahoogroups.com>
> > ReplyTo: electricboats@yahoogroups.com
> > Subject: [Electric Boats] Re: Catalina Conversion
> >
> > I've been going around and around with a battery decision. I'm thinking (4) Trojan T1275 at around $900.00 or (4) Odessey Pc2150 around $1200. Trojans are wet lead acid 150amps@20hr and the Odessey is AGM 100 amps@20hr.
> > Any thoughts?
> >
> > --- In electricboats@yahoogroups.com<mailto:electricboats%40yahoogroups.com>, "Doug" <dj2210@> wrote:
> > >
> > > Hi All
> > > Thanks for all the great info on this site I have begun the electric repower of my Catalina 27 sailboat. The Atomic 4 is disconnected and awaiting removal slated for this Wednesday. On the bench in the garage is a Mars BLDC motor mounted on a 2:1 gear reducer with a Kelly controller. I have had a chance to try both the Kelly controller and a Sevcon gen4 on the bench and both work equally well unloaded. I still need to choose batteries and manufacture mounts for motor and batteries. I don't expect to be operational for at least a month so in the meantime if the wind is favorable a trolling motor will help me out the slip.
> > > Doug
> > >
> >
>
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