How many cranks from a battery?

[peter2407]

I am about to install a 110Ah new battery that I expect to be charged to c. 14v (currently on charge and a meter test shows 13.5v). I have a Yanmar 30 engine, with "standard" starter motor. Assuming a crank time (ie starter button pressed) of say 15 seconds (sounds a little, feels a lot), how many cranks can I expect before the battery is too weak to be of any use? South coast based, this time of year, boat very dry and insulated, but no engine activity (except a failed attempt at starting a few weeks ago, hence the new battery). Thanks in advance.

 

[rivonia]

Are you using a deep cycle or a cranking battery?

Peter

 

[rafiki_]

Peter, I always crank Rafiki's engine for 2 blocks of 15 secs in order to get some oil around the engines before I allow them to fire up. Never been a problem with the 110ah battery even when left for a few weeks.

 

[forelle541]

Are you using a deep cycle or a cranking battery?

Peter

Battery will still only be 12.7v when fully charged even if you are charging at 14v. Let it stand for a bit then check it.

 

[peter2407]

This one

Hi Peter

This battery:http://www.yachtmailchandlery.com/110ah-powermax-leisure-battery/

But my question isn't about longevity, it's about cranks per session rather than during the life of.

I know it's not labelled as primarily being a cranker btw.

Are you using a deep cycle or a cranking battery?

Peter

 

[john_morris_uk]

Its a really challenging question to answer for several reasons.

A few seconds of cranking is only a fraction of the Ah stored in the battery. (15/3600x200 amps is less than one amp-hour of charge) If you have 55 useable amp hours (i.e. only 50%) of your 110 Ah battery then you should get at least 50 15 second starter bursts.

Unfortunately life isn't that simple.

First of all, nearly all the batteries that we use on boats won't like being asked to give 200 amps time after time. You will destroy the battery very quickly if you are not careful.

Secondly your starter motor would have to be given time to cool down or you'll burn that out as well.

Not sure if that helps or not...!

 

[pvb]

A few seconds of cranking is only a fraction of the Ah stored in the battery. (15/3600x200 amps is less than one amp-hour of charge) If you have 55 useable amp hours (i.e. only 50%) of your 110 Ah battery then you should get at least 50 15 second starter bursts.

Unfortunately life isn't that simple.

It certainly isn't. Taking 200A as the starter current (which I think is too high), a typical 110Ah battery would be reduced to 50% charge in less than 6 minutes, so only about 23 lots of 15-second starting.

 

[nigelmercier]

The Ah rating of batteries is calculated at a given discharge time, often 20 hours. So a 100Ah battery would give 5A for 20h. You cannot use this figure to calculate the calculate the discharge at significantly higher currents.

 

[reeac]

I've never timed it but my guess is that my VP2002 starts in 5 seconds - I would never crank for 15 seconds. In fact, since batteries suffer temporary depletion at the plate surfaces during heavy discharges it's very advantageous to restrict such discharges to less than 10 seconds and to give the battery a ca. 60 second rest between attempts to start.

 

[sailorman]

my 115Ah leisure engine battery started the 4 cylinder first touch of the key yesterday
how does your car perform on a freezing morning


QUOTE=peter2407;4038075]I am about to install a 110Ah new battery that I expect to be charged to c. 14v (currently on charge and a meter test shows 13.5v). I have a Yanmar 30 engine, with "standard" starter motor. Assuming a crank time (ie starter button pressed) of say 15 seconds (sounds a little, feels a lot), how many cranks can I expect before the battery is too weak to be of any use? South coast based, this time of year, boat very dry and insulated, but no engine activity (except a failed attempt at starting a few weeks ago, hence the new battery). Thanks in advance.[/QUOTE]

 

[rivonia]

There is a BIG difference between a leisure battery and a Cranking/car (starter) battery. A cranking battery will virtualy discharge itself when cranking (its supposed to) if you use a leisure battery the benefit is not the same as it is not meant to discharge rapidly like a cranking battery. A leisure battery is meant for SLOW discharge.

That was the reason I asked what type of battery was being used.

A cranking battery will very very quickly re-charge as that is its purpose.

Good luck

Peter

 

[john_morris_uk]

There is a BIG difference between a leisure battery and a Cranking/car (starter) battery. A cranking battery will virtualy discharge itself when cranking (its supposed to) if you use a leisure battery the benefit is not the same as it is not meant to discharge rapidly like a cranking battery. A leisure battery is meant for SLOW discharge.

That was the reason I asked what type of battery was being used.

A cranking battery will very very quickly re-charge as that is its purpose.

Good luck

Peter

True, and its made even more complicated by the fact that leisure batteries are a sort of compromise between traction batteries and cranking batteries. And we haven't even started on gel vs wet etc. I will return to my original premise, which is that number of 15 second crankings on the starter is not a simple equation to calculate.

 

[lw395]

The cranking current spec of the battery will be some hundred of amps for x minutes at some horribly cold temeprature.
Typically this works out at about a third to a half of the nominal amp-hours.
You will get a bit more if the battery gets to rest a few minutes between goes.

Once the engine is spinning, the current drawn falls off so its an equation with all unknowns, no constants....

 

[sailorman]

My last engine battery ( leisure) was removed @ 9 yr old, it was then to see service lighting a beach hut.

True, and its made even more complicated by the fact that leisure batteries are a sort of compromise between traction batteries and cranking batteries. And we haven't even started on gel vs wet etc. I will return to my original premise, which is that number of 15 second crankings on the starter is not a simple equation to calculate.

 

[john_morris_uk]

My last engine battery ( leisure) was removed @ 9 yr old, it was then to see service lighting a beach hut.

Not sure what point you are making except perhaps you treated your battery well and kept it charged and didn't abuse it and therefore it lasted a long time.

On the opposite end of the spectrum I usually despair of yachtsmen and women who casually drop into conversation that either,

a) Their cabin lights invariably go dim by the morning (which obviously indicates that their batteries are FLAT) and therefore being screwed into a downward spiral of loss of capacity. It also indicates a possible an inability to recharge them properly in the first place?

or

b) They say something like, "But they must have been fully charged, I motored out of harbour for twenty minutes this morning..." Flat batteries require HOURS of recharging to get them anywhere near 100% charge, even with a smart charge adapter. You can't force the physics of the battery.

 

[sailorman]

The point is
an engine & battery in good condition, the engine will start easily,no matter if a cranking or leisure battery is employed.
i have 3 x domestic
1 x engine
all the same battery type

Not sure what point you are making except perhaps you treated your battery well and kept it charged and didn't abuse it and therefore it lasted a long time.

On the opposite end of the spectrum I usually despair of yachtsmen and women who casually drop into conversation that either,

a) Their cabin lights invariably go dim by the morning (which obviously indicates that their batteries are FLAT) and therefore being screwed into a downward spiral of loss of capacity. It also indicates a possible an inability to recharge them properly in the first place?

or

b) They say something like, "But they must have been fully charged, I motored out of harbour for twenty minutes this morning..." Flat batteries require HOURS of recharging to get them anywhere near 100% charge, even with a smart charge adapter. You can't force the physics of the battery.

 

[oldfatgit]

The battery you have purchased is not ideal for engine start, being designed to provide sustained power at lower rates for longer times. Having said that it is not bad either being a compromise between engine start and deep cycle. By charging it as you are you can assume that it will give you enough opportunities to start the engine before you would have discharged it too much. So your question is at what point should you give up before damaging it, the starter motor or any other vulnerable components. If I were you I'd fit it and see what happens; if the engine has not fired after about 10 attempts of 15 seconds then you are flogging a dead horse and need to find out why the engine is not starting. You should allow time between attempts to let the starter motor to cool down.

If the engine starts then you need to run the engine for a while to replace the charge taken, this is a question of judgement. If it starts first time then 10 minutes should be more than enough, if, however, you have worked the battery a lot more then it might be advisable to take it home and get the national grid on the case. The way to find out for sure is to measure the voltage across the terminals a couple of hours after the last attempt or after you have stopped charging it. The table below gives you what the % charge state is given the voltage found. The point is that you should let the battery rest for about 2 hours before measuring.

So if your battery voltage is 12.2V then you have a battery at 60% and need to replace 44 Amp Hours. If your alternator is 50A then you need to run your engine a minimum of 53 minutes. However you should allow for losses so a minimum of an hour should do it. Trouble is all of this stuff takes for ever and ignores other complications such as the phenomenon of "surface charge" where a battery reports a higher voltage than it actually has.


State of Charge 12 Volt battery
100.00% 12.7
90.00% 12.5
80.00% 12.42
70.00% 12.32
60.00% 12.2
50.00% 12.06
40.00% 11.9
30.00% 11.75
20.00% 11.58
10.00% 11.31
0 10.5

 

[sailorman]

How many alternators give out full power for an hour without a smart charger

The battery you have purchased is not ideal for engine start, being designed to provide sustained power at lower rates for longer times. Having said that it is not bad either being a compromise between engine start and deep cycle. By charging it as you are you can assume that it will give you enough opportunities to start the engine before you would have discharged it too much. So your question is at what point should you give up before damaging it, the starter motor or any other vulnerable components. If I were you I'd fit it and see what happens; if the engine has not fired after about 10 attempts of 15 seconds then you are flogging a dead horse and need to find out why the engine is not starting. You should allow time between attempts to let the starter motor to cool down.

If the engine starts then you need to run the engine for a while to replace the charge taken, this is a question of judgement. If it starts first time then 10 minutes should be more than enough, if, however, you have worked the battery a lot more then it might be advisable to take it home and get the national grid on the case. The way to find out for sure is to measure the voltage across the terminals a couple of hours after the last attempt or after you have stopped charging it. The table below gives you what the % charge state is given the voltage found. The point is that you should let the battery rest for about 2 hours before measuring.

So if your battery voltage is 12.2V then you have a battery at 60% and need to replace 44 Amp Hours. If your alternator is 50A then you need to run your engine a minimum of 53 minutes. However you should allow for losses so a minimum of an hour should do it. Trouble is all of this stuff takes for ever and ignores other complications such as the phenomenon of "surface charge" where a battery reports a higher voltage than it actually has.


State of Charge 12 Volt battery
100.00% 12.7
90.00% 12.5
80.00% 12.42
70.00% 12.32
60.00% 12.2
50.00% 12.06
40.00% 11.9
30.00% 11.75
20.00% 11.58
10.00% 11.31
0 10.5

 

[nigelmercier]

... Flat batteries require HOURS of recharging to get them anywhere near 100% charge

My boat partner once told me he had charged the batteries up while he went for dinner I explained that they probably need at least 24 hours.

How many alternators give out full power for an hour without a smart charger

I've got a 120A alternator, and a smart charger; I've never seen more than about 60A, and then only for a few minutes.

 

[Mistroma]

Most people have already heard that extended cranking can also allow water to enter cylinders. But, just in case anyone has missed this point.

If the engine doesn't fire then there won't be pressure to blow water from the exhaust. If the water pump has been pushing water through the elbow then it might run back into the cylinders. So it's a good idea to shut the water inlet if extended cranking is required.