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Old 08-26-2013, 02:28 AM   #1
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Genset Battery Sizing

I`m about to replace the 5 existing year old genset start battery with an identical 150 amp hour battery,the size recommended by Onan.
The battery starts a small 3 cylinder diesel. Yes, it heats glow plugs first, but that`s it. The genset has an alternator. I fitted a regulated 25w solar panel.
A PO,presumably seeing excess unused power, wired a fridge off the battery. On purchase 3 years ago, I put it back on the main board and batteries where it has a dedicated circuit-breaker/switch.
Does anyone know why the genset is recommended so much battery?
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Old 08-26-2013, 05:58 AM   #2
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Think of the noisemaker battery as your ace in the hole, a personal insurance policy !

Should the engine batts and the house batts die , either operating the noisemaker for many hours ,

OR stealing the noisemaker batt and installing it in the start position will get you going.

Best if the noisemaker batt is easily up to starting the main engine , a #27 or #31 will frequently be large enough in warm weather..
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Old 08-26-2013, 08:49 AM   #3
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Another option is to start the generator using the house bank. If there is a separate battery to start the generator the generator's alternator will be little used as it will quickly replenish the start battery. If you use the house bank then the alternator can be charging the house bank the whole time the generator is operating.

This assumes you have a separate start battery for the main engine. Or as I have on Bay Pelican a separate battery for the helm radios. Thus if the house bank goes done the separate battery can be used to start the generator.

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Old 08-26-2013, 09:16 AM   #4
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Wow! this is a timely topic for me. I need some opinions.
I just hopped the gravities on my inverter bank and have a dead cell. Batts are 6 volt Trojans and are 7 years old so its time for them to all go.
Here what I have for a system: 2-8Ds, one for each engine and they feed DC panel for house loads. 4-6v Trojans that only supply a 2KW inverter and a small electric fridge on bridge. 1-GP 27 for the genset.

I want to increase the inverter bank to 8-6v. This will require eliminating the genset battery for space reasons. With over 1300 amp-hrs of capacity on board the genset batt seams like overkill.

What do you think?
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Old 08-26-2013, 10:35 AM   #5
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You will get many opinions on the proper setup. My opinion is that a boat needs two isolated battery sources so that if one goes down the other can start the generator or engine for a recharge. After that the more you can combine the batteries the better off you are. The exception would be for a thruster battery up forward.

Bay Pelican is set up with one large bank that powers and starts everything, thus all charging and draw is done to and from one bank with an isolated battery at the helm which powers the SSB and VHF radios. Whether I am running the genset or the main engines the charge is going to this bank with a echo charger handling the isolated battery.

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Old 08-26-2013, 03:00 PM   #6
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Iím in the separate battery for the generator camp as well. Having that one battery isolated, guaranties the ability to start the gen set and recharge your flat main batteries.
I also keep a set of short jumper cables (4') on board and can jump start the mains from the generator battery if necessary.
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Old 08-26-2013, 03:19 PM   #7
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The Batterie banks on my boat:
3 Groups,
1.) consum normal 2X 4D
2.) Inverter 3X 8D
3.) Start batterie for 5 Machines ( 2 main machines, 3 Gens) 1X 8D
it∑ s only one idea.
I can all batteriebanks change with Batterie-swiches.
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Old 08-26-2013, 09:38 PM   #8
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Thanks for all the help.
IGs my vintage with twins have a pair of 200ah batteries, one to each engine, no dedicated house, you could make one 'house", alternately, and the boat automatically combines both for starting.
So the genset is essential back up, so is its battery, I see the virtue of it doubling as an extra start battery.
I tried connecting a main battery to the genset one with leads, the starter motor kicked in properly unlike before, but did not start it, I think power was sucked into the dud genset battery,now ordering a new lead acid one, $300 the best price so far.
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Old 08-30-2013, 07:34 PM   #9
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Here is another option that recently helped a boat in the middle of the Pacific, where the generator battery had ben run flat, apparently due to a fault in the charging system.

They used a 12V lithium emergency battery starter kit to crank up the genset and saved the day.

Here is the link: www.smart-giant.com/store/index.php

I have one for my dinghy and car, check the specs, it can recharge 5V, 8V, 9V, 12V, 16V, 19V and 24V.

It can ONLY start 12V engines....
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Old 08-30-2013, 08:15 PM   #10
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Good result. Adding a small, say 25w, solar panel for the genset battery maintenance may help.
I`m about to pick up the new battery for my Onan 6.5kw genset. The recommended 150ah battery now packs 1150CCA, that should start most things on recreational boats.
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Old 09-05-2013, 09:01 AM   #11
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I have a single group 24 as dedicated generator start battery it always starts my 8k Westerbeke with no problem
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Old 09-05-2013, 09:15 AM   #12
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Group 24 for my Westerbeke 8Kw
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Old 09-05-2013, 10:41 AM   #13
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Dedicated group 24 for my Kohler 4Kw
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Old 09-06-2013, 06:41 AM   #14
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<The recommended 150ah battery now packs 1150CCA,>

A batt rated in AH is usually a deep cycle batt , and if honest the AH will be at a 20 hour rate.

A single deep cycle batt is usually not good for starting.

A batt measured in CCA is a start batt and fairly useless at anything else.

Be sure to purchase what you require.
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Old 09-06-2013, 09:29 AM   #15
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Dedicated group 24 for my Westerbeke 7.5 kw
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Old 09-07-2013, 06:28 AM   #16
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Dedicated group 24 for my

24 like 27 like 31 or 4D or 8D is a SIZE , it is not a battery TYPE.

To start well a START built internally batt is required, regardless of its size.
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Old 09-07-2013, 01:56 PM   #17
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Here's what we do on our Island Pilots.

1. House bank - 4 ea AGM 8Ds - about 1,000 AH.
2. Engine start - 1 ea AGM 8D (same battery as house bank)
3. Generator start - 1 ea AGM sized for 7kW.
4. Battery combiner so that whenever a charging current is available, either from shore power or engine alternators, joins house and engine start battery into a single bank. Connects and disconnects automatically so you can't discharge all batteries by mistake. Has manual over-ride for "jump" starting the engines.
5. Isolated charge from charger/inverter to generator starting battery - this battery remains isolated so is available if engine start and house bank become depleted.

By matching the start battery with those that make up the house bank, all 5 8Ds charge equally when combined. Combiner will not join batteries if too large a voltage differential exists.

On our DSe we have a completely different battery set up.

1. Main bank is made up of 1,00" AH LiFePo4 cells - 48v at 1,000 AH (equivalent to 4,000 AH at 12v).
2. Engine start. 2 ea.AGM charged by 120VAC/12v charger that runs from the 3.6kW inverter and engine alternators.
3. 3kW shore charger for main battery.
4. 6kW solar array with 2 ea 60 amp controller/chargers.

With this set up, the main battery never becomes totally discharged so there's plenty available to start the diesels.

BTW, this set up is not the norm. But most cruising yachts don't have the option of electric cruising.
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Old 09-07-2013, 09:06 PM   #18
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Quote:
Originally Posted by FF View Post
<The recommended 150ah battery now packs 1150CCA,>

A batt rated in AH is usually a deep cycle batt , and if honest the AH will be at a 20 hour rate.

A single deep cycle batt is usually not good for starting.

A batt measured in CCA is a start batt and fairly useless at anything else.

Be sure to purchase what you require.
Thanks for the tips.
The new 1150AH battery is start designated. The "150AH" description is probably a carry over from describing deep cycle batteries, it defines size/dimensions than anything else. We don`t have descriptors like your "8D", which on reflection may be more helpful.
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