Reply
 
Thread Tools Search this Thread
 
Old 24 August 2012, 17:19   #1
Member
 
Country: UK - England
Town: I.O.W/Bristol
Boat name: HotShot
Make: shakey
Length: 5m +
Engine: 70hp Tohatsu
Join Date: Jul 2003
Posts: 1,543
Battery size for 90hp Outboard

So I'm looking into getting a 90hp Tohatsu TLDI engine. Tohatsu have told me I need a 120Ah, 700CCA (850MCA) battery for it (which weighs about 28-30kg). Now as far as I was aware, these engines ran on petrol, not electricity and I'm no battery expert but it appears that this battery is huuuuuge. The helpful guy at Tohatsu told me this is the battery I need and I could use something of lower capacity but it could result in errors being logged on the engine management system and eventually a a shut down into limp mode.

Given that the Tohatsu guy seems to know his stuff, I will get this battery but I'm just curious as why a 90hp engine needs a battery big enough to power a small town. Is anyone running one of these engines, or an optimax equivalent, with a smaller battery than this without any problems?

Thanks in advance.

Tim
__________________

__________________
slimtim is offline   Reply With Quote
Old 24 August 2012, 22:39   #2
Member
 
Country: USA
Town: Oakland CA
Length: 3m +
Join Date: Feb 2005
Posts: 6,653
Need to be able to crank the motor, which is why it's huge.

Trust the manufacturer; they've been there before.

jky
__________________

__________________
jyasaki is offline   Reply With Quote
Old 25 August 2012, 04:04   #3
RIBnet supporter
 
Ian M's Avatar
 
Country: UK - England
Town: New Milton
Boat name: Jianna
Make: Osprey
Length: 6m +
Engine: 200 E-TEC
MMSI: 235076954
Join Date: Sep 2004
Posts: 1,933
Mmm, I'm not a battery expert, but I seem to remember reading that the CCA rating (cold cranking amps) is the measure of a batteries ability to turn an engine over, and it is not the capacity (amp hours), or in basic terms, the amount of electricity, that the battery is able to store? This is why you have starter batteries, able to supply large currents quickly (thin plates) and deep discharge batteries, that can hold a large charge and are able to deliver a reasonable current over a long period of time (thick plates!) without distorting. Or have I been at the mushrooms again
__________________
Ian

Dust creation specialist
Ian M is offline   Reply With Quote
Old 25 August 2012, 06:54   #4
Member
 
Country: UK - England
Town: I.O.W/Bristol
Boat name: HotShot
Make: shakey
Length: 5m +
Engine: 70hp Tohatsu
Join Date: Jul 2003
Posts: 1,543
Quote:
Originally Posted by jyasaki View Post
Need to be able to crank the motor, which is why it's huge.

Trust the manufacturer; they've been there before.

jky
Yes of course but a FAR smaller battery will crank the motor. Its not a big motor, 90hp, 3 cyclinder, 1.3 litres. Much smaller batteries turn bigger car engines. As I said, I will get the battery he recommends because this guy really knows his stuff and is extremely helpful but I'm just curious as to why and wondered if anyone else has had any experience of running smaller batteries.

I read somewhere that the compressor for the fuel injection requires a bigger battery but shouldn't the engine's alternator supply all the current required when the motor is running? If it didn't, the battery would just drain away as you used it.

Ian M, its been a while, how are you? Yes I think you're right there which is even more puzzling to me because the Ah are a measure of supplying a certain current over a long period (i.e. to power electronics and lights etc. in a boat/motorhome when at rest) which doesn't really apply to an engine battery as the alternator should be able to do this while its running. For the record, I have minimal electronics on my boat, some gauges a fish finder and a bilge pump.

Cheers,

Tim
__________________
slimtim is offline   Reply With Quote
Old 25 August 2012, 07:07   #5
Member
 
ashbypower's Avatar
 
Country: UK - England
Town: Salisbury/Poole
Boat name: Blue C
Make: XS 600
Length: 6m +
Engine: 125hp Opti
MMSI: 235082826/235909566
Join Date: Jan 2004
Posts: 1,439
Tim, you have hit the nail o the head.
The compressor needs to turn quite fast to supply the air pressure required.
Now this is a load on the battery in addition to the starter motor load.
When High current is taken,voltage drops, due mainly to the internal resistance of the battery. Now if this voltage drops below a certain threshold the ECU will detect this and this will cause a fault code et al..
Our Optimax engines all have high CCA batts and we never have a problem, you must remember however that an opti will never start first turn of the motor it WILL take 2 perhaps 3 turns to build up the air pressure.
__________________
Brian C
Harbour Sea School & APS Marine Centre
ashbypower is offline   Reply With Quote
Old 25 August 2012, 08:27   #6
RIBnet supporter
 
Ian M's Avatar
 
Country: UK - England
Town: New Milton
Boat name: Jianna
Make: Osprey
Length: 6m +
Engine: 200 E-TEC
MMSI: 235076954
Join Date: Sep 2004
Posts: 1,933
Quote:
Originally Posted by slimtim View Post
Ian M, its been a while, how are you?
Fine thanks Tim, still bumbling around the Solent, but I think you have been on your travels?
__________________
Ian

Dust creation specialist
Ian M is offline   Reply With Quote
Old 25 August 2012, 08:29   #7
Member
 
Country: UK - England
Town: I.O.W/Bristol
Boat name: HotShot
Make: shakey
Length: 5m +
Engine: 70hp Tohatsu
Join Date: Jul 2003
Posts: 1,543
I live in Switzerland now which means boating has been exchanged for mountain biking and skiing. I still wish I could bumble around the solent more regularly though :-(
__________________

__________________
slimtim is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off





Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -5. The time now is 18:17.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.