What size engine start battery?

PabloPicasso

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I want to upgrade from a single lead acid 12v battery (80 a/h) by adding a dedicated engine start battery.

I have a volvo 2001 single cylinder 7.5hp diesel engine. What is the smallest battery in (amp/hours) I could reasonably install?
 

maxi77

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If it is a reliable started then you can probably get away with something suitable for a small deisel car. In fact you may even see better starting because the ability to give more starting amps helps give the engine a good starting kick.
 

VicS

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Iti s cranking amps that count not Ah capacity. Volvo recommend a max of 70Ah for the 2001/2/3 range but unfortunately do not specify a CCA. You actually use a very small fraction of the battery capacity.

A specialist starter battery that delivers a high cranking amps from a battery with a small Ah capacity and small physical size may suit your needs if space is a consideration.

A small Red Flash battery for example http://www.tayna.co.uk/Red-Flash-900-Battery-P7572.html or http://www.tayna.co.uk/Red-Flash-750-Battery-P7566.html
They are however expensive by any standards.

If space is not an issue any small car starter battery should do the job.
 

Topcat47

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I'm currently using a motorcycle Battery. The theory was:-"If it can start an 800cc bike, it ought to be able to swing a 300cc diesel". It struggled when I was priming the fuel system at the start of the season but worked well the rest of the time.
 

Tranona

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Suggestion for a small dedicated start battery is good. As stated any battery for a small car will do or if you are short of space and rich use a Red Flash or Odyssey. Then fit the biggest capacity battery you can for your house needs. Best if you have automatic split charging such as a VSR and independent plus parallel for the 2 separate circuits. Thast way the engine start is chrges first and you always have the option to use the house if the engine battery does fail.
 

barnaclephill

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I have a 40-year old Yanmar diesel, 8HP.
A few years ago I used 600 CCA batteries for small diesel cars (4WDrives, etc),
In my logbook I then went on to a 550 CCA, 120RC, 75 A/hr battery.

In my logbook the battery I got in October is 550 CCA, 95 RC, 58A/hr. I think it's made of lead & calcium because it was only about 12kg, it is sealed, and came with a 3 year warranty. Model number X55D23C, I think it's Exide.

I do suspect that I could go for 500 CCA, maybe next time. The boat only came with one battery, but I split the system to have a dedicated starter (and some small lamps) and everything else off a house battery, currently about 120 A/hr.

All this is working well.
 

Plevier

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Pure lead, lead antimony, lead calcium, lead tin, lead silver; none of these will have any effect on battery weight.
All of them - other than lead - are just alloying elements used in small proportion with the lead to modify mechanical (and to a much lesser extent electrical) properties. Calcium when used is usually around 0.1% if I remember correctly. Antimony is normally about 1.5%. (You don't get them together.) Tin, silver etc in tiny proportions.
They are all lead-acid batteries with only minor differences in characteristics.

Turning to the original question, I would have said anything from about 350CCA or 35Ah upwards. I can never understand why people fit such monster batteries to tiny engines. Look at the small batteries used in big motorbikes.

Red Top, Odyssey etc are very good starting batteries if you really want to save space and weight.

PS X55D23C is an Exide Aus/NZ battery. It's lead plus calciuma nd silver. They don't quote an Ah figure but the reserve capacity is 105 i.e. it will give 20A for 105 minutes suggesting an Ah capacity of maybe around 40, I doubt as much as 58.
 
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The engineer

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Bleeding

With a motorcycle, you do not need to bleed the fuel system on a cold morning in the middle of the North sea. Also a higher compressionin ratio is found on a diesel, well more than my bike anyway!
A larger battery than a bike is a good idea.
 

Plevier

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I agree, I was just drawing a comparison.
Similarly with the Red Top you can certainly start with about a 15Ah one when all goes well but it gives you no reserve for the day when it's slow.
I believe my suggestion of around 35-40Ah is a reasonable compromise, your judgement may be different.
 

vyv_cox

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I want to upgrade from a single lead acid 12v battery (80 a/h) by adding a dedicated engine start battery.

I have a volvo 2001 single cylinder 7.5hp diesel engine. What is the smallest battery in (amp/hours) I could reasonably install?

The 1, 2 and 3 cylinder Yanmar engines have starter motors listed as 200 CCA, so it seems reasonable to assume the Volvo ones won't be miles different.

I use a Red Flash 900 AGM battery to start my Yanmar 3GM30. Its advantage is that it is small and can be mounted any way up, if that helps. I chose it so that I could install it in the tunnel next to the gearbox.

April036.jpg


For my engine it is a little small. It will start it fine in normal conditions but I can imagine it would struggle if the engine didn't fire immediately. For your engine I imagine it would be perfectly adequate.
 

Plevier

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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.
 

Plevier

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As VicS said it's CCA (Cold cRanking Amps) that matter not Amp hours. We and most boats we know use 100 CCA batteries. If you use less you get less attempted starts.

If the engine starts quickly you're right, it's all about CCA, but if you get into repeated attempts the Ah becomes more significant. Not because the battery is flat but because the high current capability drops with the state of charge. On a battery where the CCA is a higher multiple of the Ah, such as the Red Flash or Red Top, the effect is more pronounced.

Do you really mean 100CCA? That's very small. VicS's little battery is 156CCA and has nothing to spare.
 

Topcat47

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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?
 
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