starter batterie: 95ah or better 120ha

[Orthop]

Hi,
the original starter battery was 120ah, agm technique, for a VP D4 300. The guy at the shop said I can use as well a 95ah battery (also agm).
Every engine has its own starter battery, I do not need the battery for life onboard (separate batteries 2x210ah).
Can anyone give me some advice?
Thanks

 

[Oscar24]

I would replace like for like rather than risk a slightly smaller capacity battery tbh.

 

[BruceK]

I think it's wrong to think of starter batteries with Ah in mind. It's a pretty useless measure as far as a starting battery is concerned. What you are after is CCA, cold cranking amps. If the CCA matches then you should be perfectly fine.

 

[QBhoy]

Bruce K has it spot on.
All about the CCA rating.
Usually starter batteries differ from leisure batteries. In term of starting ability it’s about the CCA. For leisure, it’s more about the AH.
That said. You can now get dual purpose batteries. Bit like a motor sailer though. They aren’t usually good at both, haha.
I’d also say that the choice may be down to things like if you have a linked battery system. Different ratings or sizes in batteries linked together is never good. The weaker can take from the other and ruin both.

 

[Orthop]

Thanks Bruce, did a little research and found different units for CAA, e.g. sae and en. Does anyone know the right CCA for the VP D4 300?
Are there any further problems if using not the right CCA, for example for the starter motor?

 

[Orthop]

Thanks Q... of course I will renew both starter batteries... and they are linked together...Perhaps someone can say something about the correct CCA for my engines?

 

[Croftie]

According to
https://www.google.com/url?sa=t&rct...ons/47709267&usg=AOvVaw0V5TyFi6MD9xKWlFAsRQ1t

Battery
Minimum requirements for cold start:
• 12V, 1150 CCA for D4 engines
• 12V , 2300 CCA for D6 engines

If you have 2 starter batteries in parallel then your could get away with less than 1150 each, prob 900 should be OK assuming you don't try to start both at the same time.

 

[BruceK]

.....
Are there any further problems if using not the right CCA, for example for the starter motor?

Not if it's higher. If the battery cannot deliver the amperage to turn the starter motor a curious thing happens which I cannot explain the physics of, but in a nutshell the loaded battery voltage then drops too much. To compensate the starter motor draws more amps as a result of the lower voltage in order to do the work required (it doesn't just quit). So the battery cables and starter motor will get very hot indeed with resulting damage. You will probably have noticed this yourself when trying to start an engine on a low charge battery. It can also cause the battery cell plates to warp

 

[LittleSister]

Thanks Bruce, did a little research and found different units for CAA, e.g. sae and en.

Though I'm well aware of the general significance of CCA (cold cranking amps), I've always intended to investigate the difference between SAE and EN measurement of it. This thread has finally prompted me to do just that, and here's what I found on t'internet. (Happy to be corrected.)

In short, SAE and EN measurement of CCA is similar in method and resulting figure (value), but SAE will give a slightly higher figure (within about 10%, it seems) for the same battery.

(There are numerous other standards, most of which we are less likely to come across, but note that MCA (Marine Cranking Amps) is measured at a higher temperature (0 degrees rather than minus 20), resulting in a CCA figure about 25% higher than SAE for the same battery.)

SAE is an American standard, and is probably what is being specified if your engine comes from USA or Far East. EN is a European standard, and is probably what is being specified if your engine comes from Europe. For batteries, if the CCA is not specifically indicated to be EN, I'd assume it was SAE.

Both SAE and EN measure at a very low temperature (at which batteries don't work to full potential) how much current the battery can deliver for a specified time, before falling to a specified voltage.

The table at the following link gives equivalent values for SAE and EN, and two other standards unlikely to be relevant to us. (I do have doubts whether the relationship can really be that linear, but I imagine it is good enough for our purposes). https://battery-service.com/support/cca/

Scroll down to 'Cold Cranking Performance (Amps)' in the following link and you will find a summary of how each CCA standard is measured and how they relate to one another. https://www.yuasa.co.uk/info/technical/understanding-the-specifications/

 

[Assassin]

Not if it's higher. If the battery cannot deliver the amperage to turn the starter motor a curious thing happens which I cannot explain the physics of, but in a nutshell the loaded battery voltage then drops too much. To compensate the starter motor draws more amps as a result of the lower voltage in order to do the work required (it doesn't just quit). So the battery cables and starter motor will get very hot indeed with resulting damage. You will probably have noticed this yourself when trying to start an engine on a low charge battery. It can also cause the battery cell plates to warp

Slightly wrong there Bruce.

Usually with a low battery or inadequately sized battery it does indeed compensate with voltage and this creates an entirely different issue.
Most engines are electronically controlled and when it cranks it has to have a minimum voltage going to the electronics for them to work; and this situation drops the voltage so low during cranking that the electronics simply don't work due to too low a voltage.

The rest is spot on.

For MAN, Volvo, and newer DD's this is 9.5 volts for 12 V systems, and 20 V for 24 V systems.

 

[Orthop]

According to
https://www.google.com/url?sa=t&rct...ons/47709267&usg=AOvVaw0V5TyFi6MD9xKWlFAsRQ1t

Battery
Minimum requirements for cold start:
• 12V, 1150 CCA for D4 engines
• 12V , 2300 CCA for D6 engines

If you have 2 starter batteries in parallel then your could get away with less than 1150 each, prob 900 should be OK assuming you don't try to start both at the same time.

This data sheet describes "the the powerful SOLAS approved range for use in fast rescue boats:". Is this also standard in the normal say standard range of VP?. If this is correct the original installed starter batteries had too low CAA...

 

[Orthop]

Though I'm well aware of the general significance of CCA (cold cranking amps), I've always intended to investigate the difference between SAE and EN measurement of it. This thread has finally prompted me to do just that, and here's what I found on t'internet. (Happy to be corrected.)

In short, SAE and EN measurement of CCA is similar in method and resulting figure (value), but SAE will give a slightly higher figure (within about 10%, it seems) for the same battery.

(There are numerous other standards, most of which we are less likely to come across, but note that MCA (Marine Cranking Amps) is measured at a higher temperature (0 degrees rather than minus 20), resulting in a CCA figure about 25% higher than SAE for the same battery.)

SAE is an American standard, and is probably what is being specified if your engine comes from USA or Far East. EN is a European standard, and is probably what is being specified if your engine comes from Europe. For batteries, if the CCA is not specifically indicated to be EN, I'd assume it was SAE.

Both SAE and EN measure at a very low temperature (at which batteries don't work to full potential) how much current the battery can deliver for a specified time, before falling to a specified voltage.

The table at the following link gives equivalent values for SAE and EN, and two other standards unlikely to be relevant to us. (I do have doubts whether the relationship can really be that linear, but I imagine it is good enough for our purposes). https://battery-service.com/support/cca/

Scroll down to 'Cold Cranking Performance (Amps)' in the following link and you will find a summary of how each CCA standard is measured and how they relate to one another. https://www.yuasa.co.uk/info/technical/understanding-the-specifications/

found this:

View attachment CCA: DIN, EN, SAE???.pdf

 

[Rocksteadee]

The electrickey to apply for the increased current at a lower voltage is ohms law V/A = R. R being the resistance of the motor.
Assume R is fixed, voltage goes down so current goes up

 

[BruceK]

We all know the equation, it's the physics behind the equation that is baffling. Like why the PD should drop in the first instance. One naturally would be inclined to think the PD would be a constant if R is a constant. Right?

I'm not sure R is right either. Work done is W and if no work is being done V still decreases while A increases

 

[Croftie]

The electrickey to apply for the increased current at a lower voltage is ohms law V/A = R. R being the resistance of the motor.
Assume R is fixed, voltage goes down so current goes up

Probably wrong here but R will not be fixed, as the motor works it produces heat and as the winding's heat up (remember the BT is probably taking 300+ amps) its resistance will change.

 

[Rocksteadee]

Probably wrong here but R will not be fixed, as the motor works it produces heat and as the winding's heat up (remember the BT is probably taking 300+ amps) its resistance will change.

Hence the word “assume”. Making a complicated answer easier