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Old 20-10-2014, 06:04   #1
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Batteries

Hi all... We have decided to change our batteries, and I'm sure this topic must have come up before but it is a minefield of information and contradictions that I was hoping for some help with.

We need approx. 360ah for the house system, and are looking at 2 180 batteries. I have been recommended wet cell lead acid batteries any thoughts?

My other question is about the engine battery.. we are in a catamaran with 2 (new) yanmar 3ym30 engines, currently starting off a 120ah battery which is unmarked but I think it is a deep cycle with low cca. The engines require 70 amps, 385cca 455mca. I am looking at getting a minimum of 100amps but am unsure as to the advantages of having 2 batteries in parallel or if 1 decent battery would work just as well.. again, any help would be greatly appreciated. We are in the Greek Islands and can order the battery we need but the best info I can get off the guy in the shop is that they are all "very good batteries". ..
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Old 20-10-2014, 06:39   #2
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Re: Batteries

For starting a single battery is best. I assume you will have one starting battery for each engine?

What kind of battery for the house bank is certainly an issue with many opinions.

My opinion I went with standard FLA (flooded lead acid) batteries. My reasons.

- This type is most tolerant of abuse, under charging or over charging, etc without killing it.

- Less expensive than any other type of battery.

Not sure about Greece but in the US the best option is to go with pairs 6 volt batteries like are used in golf carts, fork lifts, etc. They are smaller so easier to handle, less expensive, and are true deep discharge batteries.
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Old 20-10-2014, 06:56   #3
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Re: Batteries

Quote:
Originally Posted by skipmac View Post
For starting a single battery is best. I assume you will have one starting battery for each engine?

What kind of battery for the house bank is certainly an issue with many opinions.

My opinion I went with standard FLA (flooded lead acid) batteries. My reasons.

- This type is most tolerant of abuse, under charging or over charging, etc without killing it.

- Less expensive than any other type of battery.

Not sure about Greece but in the US the best option is to go with pairs 6 volt batteries like are used in golf carts, fork lifts, etc. They are smaller so easier to handle, less expensive, and are true deep discharge batteries.
Thanks Skipmac, The engine batteries are not separated. 1 bank starts both engines, we originally bought it with 2 batteries but I swiftly removed 1 which was on its last legs and it has worked fine with just the one. The new engines also turn over very easily (for now), I am just not sure if we need 2, or if there is any advantage to having 2..
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Old 20-10-2014, 07:58   #4
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Re: Batteries

Hi,
A few months ago I bough four Trojan T-105 batteries (each 6V, 225 Ah) from Athens from Dimitris Kapetanakis, Automotive Solutions Ltd. Excellent service and I'm super happy with the batteries. Dimitris' contact details and couple of other battery suppliers can be found here. They also deliver the batteries to islands.
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Old 20-10-2014, 08:25   #5
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Re: Batteries

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Hi,
A few months ago I bough four Trojan T-105 batteries (each 6V, 225 Ah) from Athens from Dimitris Kapetanakis, Automotive Solutions Ltd. Excellent service and I'm super happy with the batteries. Dimitris' contact details and couple of other battery suppliers can be found here. They also deliver the batteries to islands.
I would also endorse the T-105s. Hard to go wrong with these.
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Old 20-10-2014, 08:33   #6
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Re: Batteries

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Originally Posted by Joben View Post
Thanks Skipmac, The engine batteries are not separated. 1 bank starts both engines, we originally bought it with 2 batteries but I swiftly removed 1 which was on its last legs and it has worked fine with just the one. The new engines also turn over very easily (for now), I am just not sure if we need 2, or if there is any advantage to having 2..
The only advantages I see to having 2 starting batteries in a cat.

First one engine must be far from the battery so unless you have extra sized cables to that engine it will see some voltage drop when starting. Since starting draws a LOT of current, a voltage drop might be a problem if your starting battery is just a bit low. Also, long term low voltage to a starter puts more strain on it and might shorten the life of the starter motor.

The other thought, 2 starting batteries gives you one more backup. If you have plenty of house battery that can be a backup starting source, as long as you keep the staring battery isolated then that is probably enough.
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Old 20-10-2014, 08:57   #7
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Re: Batteries

Thanks for your help. I will go with 1 X 120 amp for both engines and extra amperage on the house batteries for back up..
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Old 20-10-2014, 09:58   #8
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Re: Batteries

It is possible to get a voltage relay with fitted to each engine battery inexpensively to allow you to have them charge and recharge and in use as house batteries and then "fall out" of the system at say 12.6v to avoid either failing to recharge or discharging right when you red them, Gives the added advantage of extra house capacity.
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Old 26-10-2014, 14:37   #9
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Re: Batteries

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Originally Posted by skipmac View Post
The only advantages I see to having 2 starting batteries in a cat.

First one engine must be far from the battery so unless you have extra sized cables to that engine it will see some voltage drop when starting. Since starting draws a LOT of current, a voltage drop might be a problem if your starting battery is just a bit low. Also, long term low voltage to a starter puts more strain on it and might shorten the life of the starter motor.

The other thought, 2 starting batteries gives you one more backup. If you have plenty of house battery that can be a backup starting source, as long as you keep the staring battery isolated then that is probably enough.
I assume the OP doesn't start both engines simultaneously so he can start the engine closest to the battery first and then the battery will be receiving charge which will assist in starting the second engine. No problem.
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Old 26-10-2014, 15:22   #10
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Re: Batteries

Are you sizing your bank properly? 360 ah on a house bank for a cat seems small to me. It does not give you much wiggle room for cloudy days or days where your usage will spike. Don't want this to go sideways, just want to make sure you know what your requirements are before purchase.


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Old 26-10-2014, 19:02   #11
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Re: Batteries

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Originally Posted by ghostlymoron View Post
I assume the OP doesn't start both engines simultaneously so he can start the engine closest to the battery first and then the battery will be receiving charge which will assist in starting the second engine. No problem.
sure it works until something goes wrong in the electrical system or the battery. the whole point of 2 engines is safety and reliability. half that goes out the window if both are on the same battery. every boat should have a starting battery for each engine

and yes 360 is pretty small

I would go min 4 golf cart which is around 440. and probably higher depending on what you have on the boat.
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Old 27-10-2014, 15:56   #12
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Re: Batteries

Joben, for starting an engine, a huge amount of current is drawn from the power source and in case the two batteries you are using are at a different charge level, it’ll just short the engine because a that huge amount of current would just flow from one battery to the other instead of both batteries powering the circuit. You can use different batteries for each engine. Make sure these batteries are high performance and can supply up to 100A peak current. I had some issues with the engine batteries recently, just thought I should let you know.
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