I have a 20HP, 2QM20, Yanmar onboard my 1981 36 footer. I need to buy a new starting battery and am wondering what to look for as far as Cranking Amps. This is a isolated battery whose sole job is to start the Yanmar. I know about the different types of batteries just need to know about the MCA. Thanks to all, in advance. toby
- Status
Largest your wallet can handle
I say this because I REALLY like the idea of having spares for critical systems aboard. Your starting battery may be isolated now, but if you're in trouble with a weak/dead house battery and no fuel for the Yanmar, the starting battery is a great way to power a VHF, emergency lighting, etc... Besides, I'm not sure I've ever heard of a condition where there were "too many cranking amps". ;o) --Jon Bastien H23 '2 Sheets to the Wind'
I say this because I REALLY like the idea of having spares for critical systems aboard. Your starting battery may be isolated now, but if you're in trouble with a weak/dead house battery and no fuel for the Yanmar, the starting battery is a great way to power a VHF, emergency lighting, etc... Besides, I'm not sure I've ever heard of a condition where there were "too many cranking amps". ;o) --Jon Bastien H23 '2 Sheets to the Wind'
Why Cranking AMPS?
I understand the differences between a starter battery with it's cranking ability and standard house batteries. I do not understand why you need those cranking amps. I have three identical Gels, and the battery switch position 1 is just the starter battery. But the standard Gel has more than enough cranking power. So why have a mix of batteries?
I understand the differences between a starter battery with it's cranking ability and standard house batteries. I do not understand why you need those cranking amps. I have three identical Gels, and the battery switch position 1 is just the starter battery. But the standard Gel has more than enough cranking power. So why have a mix of batteries?
My sediments exactly
Ed: Your comment reflects my sediments exactly. I have the same setup and have always wondered WHY do THEY mix the types of batteries in the system.
Ed: Your comment reflects my sediments exactly. I have the same setup and have always wondered WHY do THEY mix the types of batteries in the system.
You dont HAVE to have a starting battery...
You can indeed use identical deep discharge batteries for both starting and house banks. Because of differences in construction, however, usually a larger Deep Cycle battery (Group 27 or even 30 for some engines)will be required to deliver the same MCA rating.
You can indeed use identical deep discharge batteries for both starting and house banks. Because of differences in construction, however, usually a larger Deep Cycle battery (Group 27 or even 30 for some engines)will be required to deliver the same MCA rating.
Starting battery can be smaller and cheaper.
You do not need a big heavy duty recycleable battery for the starting battery. "Starting" batteries (car batteries are starting batteries, the only difference is that marine batteries as supposed to be better encased and of course cost about twice as much) have more and thinner plates that can transfer more energy (i.e. more cranking amps) than the same size recycling battery with its heavier thicker plates (which conversely allows them to survive many more deep discharge cycles). Conversely, a starting battery will accept a recharge more quickly, and you have less of the absorption rate problems (and time) that you have with recycleable batters. Starting batteries are smaller and (much) cheaper than recycleables. You should not deep discharge starting batteries (including the one in your car) except in emergencies as just a few deep discharges will kill them. Finally, because of the differences in charge acceptance and capacity, you should generally not put dissimilar batteries in the same bank, or charge your paralleled (i.e. switch set to both) dissimilar batteries over a long period of time. As far as cranking amps required, I don't think you need a lot of amps for an 18 hp diesel. Shoot, you can hand crank a 1GM, I believe. I use a typical car battery for my starting battery on my 3GM (550 cranking amps, I think) and it turns it over fine. I use the starting battery really as an emergency battery. I occassionally start and run the engine on the starting battery just to top it off with a charge. Otherwise I use the house bank for starting and everything else. I never put the batteries in parallel unless I need to charge the starting battery a bit off the AC charger (cannot isolate it), and then only for a couple hours so as not to overcharge it. Leaving your batteries in parallel is an invitation to either overcharge/undercharge them or accidently drain all you battery power which is a good way to test your sailing skills more than you anticipated. If you can afford another big recycleable battery, I'd vote to add it to your house bank (get the same size and kind as existing batteries), and use a smaller starting battery as your "emergency starting" battery.
You do not need a big heavy duty recycleable battery for the starting battery. "Starting" batteries (car batteries are starting batteries, the only difference is that marine batteries as supposed to be better encased and of course cost about twice as much) have more and thinner plates that can transfer more energy (i.e. more cranking amps) than the same size recycling battery with its heavier thicker plates (which conversely allows them to survive many more deep discharge cycles). Conversely, a starting battery will accept a recharge more quickly, and you have less of the absorption rate problems (and time) that you have with recycleable batters. Starting batteries are smaller and (much) cheaper than recycleables. You should not deep discharge starting batteries (including the one in your car) except in emergencies as just a few deep discharges will kill them. Finally, because of the differences in charge acceptance and capacity, you should generally not put dissimilar batteries in the same bank, or charge your paralleled (i.e. switch set to both) dissimilar batteries over a long period of time. As far as cranking amps required, I don't think you need a lot of amps for an 18 hp diesel. Shoot, you can hand crank a 1GM, I believe. I use a typical car battery for my starting battery on my 3GM (550 cranking amps, I think) and it turns it over fine. I use the starting battery really as an emergency battery. I occassionally start and run the engine on the starting battery just to top it off with a charge. Otherwise I use the house bank for starting and everything else. I never put the batteries in parallel unless I need to charge the starting battery a bit off the AC charger (cannot isolate it), and then only for a couple hours so as not to overcharge it. Leaving your batteries in parallel is an invitation to either overcharge/undercharge them or accidently drain all you battery power which is a good way to test your sailing skills more than you anticipated. If you can afford another big recycleable battery, I'd vote to add it to your house bank (get the same size and kind as existing batteries), and use a smaller starting battery as your "emergency starting" battery.
- Status