SOHC.co.uk Forums > CB750

Battery Amp/H question ???

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cb750stu:
Ok cheers Bryan I'll have a look for a 15 or 16ah

Cheers

Lobo:
cb750stu,

A 12v14Ah is indeed the spec battery for the '750; but by going for a 15/16Ah option, it is likely only going to be bigger - not smaller, which is your goal?

The Amp/hrs rating is only part of the picture; and in using the spec battery you should expect it'll supply 14Amps..... for one hour.

Fine, except the starter motor will draw anything from 120 -280Amps... and thus you need to consider another (battery) spec... ie CCA (cold cranking amps). Not all batteries are able to deliver very high currents, hence this CCA spec.  Definition "The rating is the number of amps a new, fully charged battery can deliver at 0° Farenheit for 30 seconds, while maintaining a voltage of at least 7.2 volts, for a 12 volt battery. The higher the CCA rating, the greater the starting power of the battery."

Point I'm trying to make is, if you're not needing to leave parking lights on an unattended bike etc, and your starting circuit etc is in good order, you may be able to get away with a smaller (eg) 10A/h battery.... so long as its CCA rating is sufficient (140 -200 CCA seems to be the typical replacement battery value). And if you only use a kickstart... well, a small'ish battery is easily on the cards as the (standard) CB750 alternator output is 13A (according to my manual) - ie well upto the job of supplying all standard CB750 running loads.

My #1 attachment below shows the stater motor current draw - ie 120A normally, and stalling @ 280Amps.

From the 2nd attachment below, for a bike in good order you'll note that the only time the alternator is not charging the battery is @ night (high beam) / 2000rpm. At all other times the battery is accepting charge - rather than 'being used'.

Finally, I'm no tech guru on this, and as I earlier suggested the fellas at Carrot Batteries may advise you of a suitable battery given the dimensions you supply them. Failing this there are likely far better informed folk on this site (K2-K6?) who may be better qualified to help.

Simon

Bryanj:
Lobo, its not as easy to get the cca for a bike battery as it is for a car so we have to use the Ahr most of the time, the people you link to sound knowledgeable and may well have all the relevant specs to hand

Yoshi823:
So as to keep weight to a minimum I have a 12v 5ah rated battery fitted to my Exup1000. It does start the bike okay & so long as I give the bike a good run it'll start okay after a few hours leaving the bike to cool down.

I found this website quite useful for battery dimensions & for buying batteries from

http://www.tayna.co.uk/Motorcycle-Batteries-C7.html

Prompt delivery as well

BigAl (Alan):
As previous posts the correct battery is a CB14L-A2 battery (14 amp hour)

The field coil & spark plug coils will always demand 2-3 amps per hour. Battery charging on these bikes starts gradually after 2K revs. Depending on your lighting design on your 'café' your may have problems with a 5 amp hour battery.

I have assumed that you intend to kick start only, if you do go for a low amp battery, fit an line switch to the black wire on the regulator-switch OFF when you kick start the bike-once warmed up switch it back ON to charge the system. The field coil will always demand 2 amps which will reduce the amount of current available for the ignition coils

Alan

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