starter battery sizing

starting batteries are rated by CA/CCA, the AH are a secondary rating, not directly relational to the cranking spec.

sizing depends on stationary, marine, or mobile operation, also diesel or gasoline.

gasoline automobile, typically 750-850 CA (2-3 CA/HP)

diesel medium truck 2,400-3,000 CA (10-15 CA/HP)

(North Central US)

To begin with you must know the size of engine you are starting. You need to know the actual current draw of the electric starter motor. Are you trying to start a scooter motor of 50 cc or a heavy duty diesel engine of 12 liter displacement. Will you need to cycle glow plugs for cold weather starting. How much energy does that require? You are not providing enough information for anyone to even make an educated guess.

Typical rule of thumb is the battery should have enough energy to complete three full starting cycles lasting 15 seconds each.

Dear Ahmed Mansour

Following parameters need to be considered.

(a) Max. current drawn by the cranking motor.

(b) Duration of the current.

(c) No. of continuous cranks which the battery has to support.

(d) Min. temp. at which the battery has to be operate.

As a thumb rule, duration of current is 10 secs. per crank & 3 such continuous cranks have to be supported by the battery.

Aging factor of 0.8 is also to be considered.

Min. operating temp. is must because battery capacity goes down with reduction in temp., since battery capacity is defined at 27 deg. Celsius.

Based on these factors, battery capacity is decided, for the type of battery under consideration.

Thanks and regards

Ashok Toshniwal, Bangalore, India

Who cares about any of this AH vs CCA . Just buy what you can afford. 12Volts is 12V

and CCA and AH will be there already.

A high quality battery will have everything you need.

"Who cares about any of this AH vs CCA . Just buy what you can afford. 12Volts is 12V

and CCA and AH will be there already.

A high quality battery will have everything you need."

My NAPA battery catalog devotes 127 pages to say exactly what you said. What a waist of paper. Why don't you send your information to them, and for that matter, you should share your knowledge with the BCI. They have been making battery selection so confusing for so long.

Thank you for spreading this information.

I COMPLETELY DISAGREE, If battery capacity is inadequate, then the engine might NEVER start because the moment, engine is cranked, VERY HIGH current is drawn from the battery, resulting in SERIOUS drop in battery voltage during that time and loss of charge, which may not allow the engine to start.

In a slightly better scenario, the battery will deliver first cranking current, but if the engine fails to crank ( for whatever reason ) and you try to crank again, then the battery is discharged or does not have sufficient charge to deliver the required cranking current.

Hello All:

Traditional battery sizing for IC engine starting need to be critically reviewed in the light of better energy sources such as ultracapacitors which can drive significantly higher currents into the starter motor due to their low ESR, have low temperature dependence and effect more reliable engine starts than conventional batteries.

Amit.

trying to be practice,i saw this with very good results:diesel engine 6 litres up to 9 litres use 160 ah, 9 to 14 litres 200ah.Sometimes it needs 24v and somebody will say "in serie conection we have a half charge and we'll need 4 batteries" but may be being that theory wright, in practice thats not necesary and you should keep those values.

Ahmed,

While Cranking amps increases with Ampere hours they are not directly associated. The construction of the battery can change the relationship enormously depending on whether the battery is needed for starting or slow discharge use.

Finding the load for your starter may not be easy, as I have found from experience. The best way is to use the engine manufacturers recommendations.

Yosemit3's suggestions are reasonable but are related to the temperatures he is likely to encounter which will be somewhat lower than yours. ( I think this is why he added his location).

Your decision will be difficult to quantify accurately as there are many factors to consider apart from the direct cranking amps such as:-

1. The temperature that you will encounter. Higher temps reduce viscosity of the oil and improve battery start capacity.

2. Your cable size & length. The CCA rating is related to voltage drop the voltage drop on the cable effectively reduces the CCA of the system.

3. The time between charge cycles. This is particularly important to you as in the high temperatures you have in Egypt during the summer 40ºC(?) you will have considerable self discharge, about 20% in 10 weeks.

4. Any loads, even light loads, that may be on while not on charge. This discharge with the self discharge could give you only a few weeks before the battery is too discharged to start the engine.

Good Luck

Chas

Higher ah means wider plates and lower internal resistance so that means higher current at starting :Buddy, if you are in problems don't face it like an starter designer forget the idea to face design,be practice or they will kick your ass!go to your supplier and just ask the starter you need for your engine!!

Hi Ferquiza,

I face this problem daily. Go learn about batteries then comeback and comment.

Who is going to give us the recommended battery for a 1000hp Mirrlees V12 JS12VT or a 1150hp PAXMAN Velanta for instance not to mention a whole host of other obscure larger diesels?

Chas

I for one would try to find the recommended battery for the application, IF we had that information from the OP.

Hi capblanc go to play chess and calm down!

A): <...Mirlees...> in the first instance, and <...PAXMAN...> in the second.

Refer to the engine manufacturer, with details of local temperature, pressure, humidity and salinity.

How about discussing the problem with (a) battery supplier(s) over the telephone, rather than waiting for educated guesses on an international Engineering forum?

That would involve waiting much quicker.