What size engine start battery?

[VicS]

Just a brief word of warning about some of the CCA figures quoted on battery suppliers websites.

IIRC a short while ago someone pointed to one of the battery manufacturers websites and it became apparent that the CCA figures given on the former were in fact the MCA figures.

CCA is the figure at 0F whereas the MCA figure relates to 32F and is approx 1.3 times the CCA

 

[Plevier]

Now you have me worried, I'm using a Yuasa bike battery with only 180CCA. Just because It worked last season, perhaps I need a little more for my 1GM10?

Should be fine as long as everything is in good condition.
You'll need to replace it more often because you have less room for deterioration than with a bigger battery, and if you have a problem with the engine you won't be able to crank for as long.
It's a judgement balance, no definitive answer, but always look on manufacturers' figures as being on the optimistic side. I know how carefully you do the tests to get the catalogue figures! Production variation can easily be 10% and then more variation depending on service conditions.

 

[Plevier]

Just a brief word of warning about some of the CCA figures quoted on battery suppliers websites.

IIRC a short while ago someone pointed to one of the battery manufacturers websites and it became apparent that the CCA figures given on the former were in fact the MCA figures.

CCA is the figure at 0F whereas the MCA figure relates to 32F and is approx 1.3 times the CCA

You'll even find some sites giving a 20deg C cranking figure!

 

[sailorman]

Should be fine as long as everything is in good condition.
You'll need to replace it more often because you have less room for deterioration than with a bigger battery, and if you have a problem with the engine you won't be able to crank for as long.
It's a judgement balance, no definitive answer, but always look on manufacturers' figures as being on the optimistic side. I know how carefully you do the tests to get the catalogue figures! Production variation can easily be 10% and then more variation depending on service conditions.

the 1GM also has hand start

 

[Topcat47]

Yeah, right! We had a competition one weekend to see if anyone could start my 1GM10 on the handle. No one could manage it, although a mate with a cobra 750 did it on his own boat to prove it was possible. The consensus was that my boat's too cramped to get a good enough swing.

 

[sailorman]

Yeah, right! We had a competition one weekend to see if anyone could start my 1GM10 on the handle. No one could manage it, although a mate with a cobra 750 did it on his own boat to prove it was possible. The consensus was that my boat's too cramped to get a good enough swing.

i have & also managed my old YSE 12 too

 

[vyv_cox]

The Red Flash 900 is rated at CCA 156A, that's at -18deg C, or 255A at 20deg C. It's only 15Ah, these batteries have fantastic high rate output. They are intended for weight and space critical applications - the technology was developed for aircraft engines and the traditional Red Top niche market (since well before AGM batteries were introduced) is car racing.

CCA figures are taken with very carefully prepared batteries.
If the battery is not brand new and fully charged the CCA will drop a lot.
A battery charged by the engine alternator only in most practical circumstances tends to sit around 80% charge.
So in practice, although this one should easily start your engine or Vyv's, you may find it marginal, and having a problem unless the engine starts immediately.
Personally I'd want a bit more margin for being undercharged or a slow start, and for the battery ageing, unless weight/space are critical.

I'm totally confused! Every marketer of Red Flash 900 that Google brings up lists the CCA as 420A. So where do your 156A and 225A come from? What standards are applicable here?

 

[savageseadog]

One also has to remember the effect of extended cranking, the battery will heat up and plates can buckle. A CCA of 100A on a small well charged battery in summer might well be OK if the engine starts first turn. However in the marine environment a good factor of safety should always be considered. Think ahead, you have a cold morning which reduces both capacity, voltage and CCA, your engine is reluctant to start, you have left your lights/instruments etc on all night the wind is getting up...............

 

[VicS]

I'm totally confused! Every marketer of Red Flash 900 that Google brings up lists the CCA as 420A. So where do your 156A and 225A come from? What standards are applicable here?

From the manufacturers website ! One assumes they are the people who know best

Red flash 900 : CCA at -18C (0F) = 156 amps, max cranking current (30 secs @ 20C) 255 amps

See HERE

Your're confused! How do you think us lesser mortals feel?

.

 

[vyv_cox]

From the manufacturers website ! One assumes they are the people who know best

Red flash 900 : CCA at -18C (0F) = 156 amps, max cranking current (30 secs @ 20C) 255 amps

See HERE

Well, yes, I would assume that also. But it would be interesting to know why Tayna and Total batteries, for example both list it as 420A, which is getting on for double the maximum discharge rate at 20C given by DMS. Seems rather dishonest. They don't make anchors do they?

 

[VicS]

Well, yes, I would assume that also. But it would be interesting to know why Tayna and Total batteries, for example both list it as 420A, which is getting on for double the maximum discharge rate at 20C given by DMS. Seems rather dishonest. They don't make anchors do they?

It not just the one taken as an example. Similar discrepancies exist across the whole range
The CCA figures on the Tayna website are all 1.8 - 2.7 times those given by DMS.

Determined on a different basis ? If so what?

 

[Marsupial]

How about approaching the problem of battery size from a different perspective. Rather than how small can it be try how long does the voltage stay above 12.5 whilst cranking? Why? well as I have said before to fry a starter motor you only need low voltage; as the voltage drops the amperage climbs (it's all about inductive load - NOT ohms law!). So for me the smallest battery is around twice the "calculated smallest size in AH" - if that makes sense. So if the maths says 35AH then fit at least 70AH and yes the CCA must be within the range required - but as others have said few if any are below and the variation in measurements is confusing.

 

[VicS]

Rather than how small can it be try how long does the voltage stay above 12.5 whilst cranking?

It wont stay above 12.5 at all! At least not unless you have a huge, ginormous battery

 

[Plevier]

I'm totally confused! Every marketer of Red Flash 900 that Google brings up lists the CCA as 420A. So where do your 156A and 225A come from? What standards are applicable here?

From DMS who are the branders of the Red Flash battery as you will see from the label on it.
See their website
http://www.dmstech.co.uk/index.htm
and the Red Flash spec sheet
http://www.dmstech.co.uk/pdfs/battery_redflash_hr_01.pdf

DMS don't actually manufacture themselves - I used to be one of their suppliers - but they specify and brand and they know what they are doing and they are honest.

Believe what they say about their batteries, not what unscrupulous retailers publicise without specifying what they mean in terms of time, temperature or end voltage.

 

[VicS]

Well, yes, I would assume that also. But it would be interesting to know why Tayna and Total batteries, for example both list it as 420A, which is getting on for double the maximum discharge rate at 20C given by DMS. Seems rather dishonest. They don't make anchors do they?

It does not expalin the reason why the CCA specs differ from those given by DMS but Tayna and Total agree with each other because they are one and the same!

Perhaps someone should contact Tayna/Total and also DMS technologies to ask for an explanation

 

[Plevier]

Well the Total site just says "420A"
http://www.totalbatteries.co.uk/i-Red-Flash-900-Battery-I7572.html
No mention of CCA or anything. Meaningless.
Could be a catalogue number!

The Tayna site does say CCA 420A.
http://www.tayna.co.uk/Red-Flash-900-Battery-P7572.html
They must have their own very non-standard definition of CCA.
It's true that there is more than one standard for CCA but differences are small.
I expect this battery would produce 420A briefly at a reasonable temperature but not to a CCA standard.

What DMS say is what you should work on.

 

[Marsupial]

It wont stay above 12.5 at all! At least not unless you have a huge, ginormous battery

funny mine does! and its not that ginormous but then I havnt burnt out a starter motor either - but many around me have.

 

[Plevier]

funny mine does! and its not that ginormous but then I havnt burnt out a starter motor either - but many around me have.

CCA specs are based on battery voltage going as low as 7.2V from a 12V battery (that's after 30 seconds which is one hell of a long time to crank).

 

[VicS]

How about approaching the problem of battery size from a different perspective. Rather than how small can it be try how long does the voltage stay above 12.5 whilst cranking? Why? well as I have said before to fry a starter motor you only need low voltage; as the voltage drops the amperage climbs (it's all about inductive load - NOT ohms law!). So for me the smallest battery is around twice the "calculated smallest size in AH" - if that makes sense. So if the maths says 35AH then fit at least 70AH and yes the CCA must be within the range required - but as others have said few if any are below and the variation in measurements is confusing.

I don't pretend to understand about inductive loads, esp in DC circuits, but my logic says that if the current increases ( as the volts fall) then the magnetic fields produced by the motor windings will increase in intensity therefore the mechanical forces produced will increase giving rise to an increased torque from the motor and consequently better cranking.

This is not what seems to happen in practice. An ailing or partly discharged battery, ie with a low terminal volts, leads to poorer cranking.

There is obviously a fallacy in my reasoning, but where?

Also how do you " calculate the smallest size in Ah".
My reasoning would be that to provide a 100amps cranking current for a small engine for 30 seconds total it would work out at a bit less than 1Ah. Double that as you suggest and you end up requiring a battery with a capacity a little less than 2 Ah.
Even I know that's rubbish so how does the calculation go?

Take my car. I know the spec for the starter motor is that loaded it takes 185 to 220 amps at a terminal voltage of 9 volts.

It is an engine that is used as the base for one of the Volvo Penta marine petrol engines. So how would you calculate the capacity of the starter battery for that engine.

 

[Plevier]

The nominal Ah capacity of a battery on an 8 or 10 hour rate (or longer) is chemically limited. You run out of active materials - generally it's lead peroxide limited (i.e. positive plate material) in a flooded battery, acid limited in an AGM battery. Deep discharge an AGM and you can end up with virtually water in it, becoming very hard to recharge, needing a very high voltage to get it started until some acid is regenerated.

Cranking amps capability for a few seconds has nothing to do with total chemical capacity or nominal Ah. It's all about internal resistance from current paths initially then as cranking proceeds, it becomes limited by temporary local acid starvation due to diffusion times. You maximise CCA by having many thin close packed plates with highly porous separators and mechanical design of the grid for lots of current carrying area and short current paths.

Empirically you can guess an approximate CCA as a multiple of nominal Ah for different styles of lead acid battery but there is no fundamental connection.

PS By grid I mean the plate framework. This is of cast (or punched) lead/lead alloy and the gaps in it are filled in manufacture with a paste which is then baked hard. The pos plate paste is lead peroxide when charged, the neg plate paste is porous lead sponge when charged, both go to lead sulphate when discharged. The lead framework is for electrical conduction from the paste, it does not contribute (significantly) to capacity. Sorry if you knew that!