Does anyone know how to figure how long it takes the standard Yanmar 3GM30F alternator (Hitachi 55 I think) to charge the batteries? We have an 8D and no fridge, etc. so I would estimate we use less that 30 Ah per day when out. The question is are there curves to figure out how long it would take to replace that 30 Ah? I've seen discussion here before saying that alternator will spit out 20-30 Amps for 1/2 hour and then drop to 5 Amps. Does that mean that it would take approx. 20*0.5+5*x = 30 - x=4 hours to recharge full? Does anyone know how to do this math? I have not found an article yet to explain it. Thanks.
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A rule of thumb is
that a deep discharge of a large bank will take an alternator 10 hours to bring back to full. And I think that's based on a bank with five times as much amp hour capacity as the rating of the alternator. BUT THAT IS JUST A ROUGH GUESS! Like we often say here, IT DEPENDS. But one thing is for sure, those slow charge times are the reason 3 stage regulators were invented.
that a deep discharge of a large bank will take an alternator 10 hours to bring back to full. And I think that's based on a bank with five times as much amp hour capacity as the rating of the alternator. BUT THAT IS JUST A ROUGH GUESS! Like we often say here, IT DEPENDS. But one thing is for sure, those slow charge times are the reason 3 stage regulators were invented.
There's no one size fits all formula
which is why you haven't seen one. You could map out some rough curves for your particular setup but state of charge, battery condition, engine/alternator RPM's and the temperatures of batteries and alternator will still be variables. It's important to understand that charging isn't linear. If your battery is empty (fully discharged) it will take what your alternator or charger is capable of putting out. This is a theoretical 55 amps in your case but even this will decrease as your alternator heats up. As your battery "fills" it will accept less and less charge. As the battery reaches a nearly charged state it will take an increasingly small charge rate, regardless of your alternator's rated output. You can verify all this with an amp monitor a la Link 10/20. Most cruisers rarely charge their batteries to 100% using their engine/alternator because charging the last 15% takes an exceedingly long time. Most charge to something around 85%.
which is why you haven't seen one. You could map out some rough curves for your particular setup but state of charge, battery condition, engine/alternator RPM's and the temperatures of batteries and alternator will still be variables. It's important to understand that charging isn't linear. If your battery is empty (fully discharged) it will take what your alternator or charger is capable of putting out. This is a theoretical 55 amps in your case but even this will decrease as your alternator heats up. As your battery "fills" it will accept less and less charge. As the battery reaches a nearly charged state it will take an increasingly small charge rate, regardless of your alternator's rated output. You can verify all this with an amp monitor a la Link 10/20. Most cruisers rarely charge their batteries to 100% using their engine/alternator because charging the last 15% takes an exceedingly long time. Most charge to something around 85%.
Couple of things
Batteries are only about 90% efficient at absorbing a charge so 55 X 0.90 = 49.5 AH is all you will get into your battery when your alternator is outputting 55 Amps for 1 hour. I find that for all this math stuff if you look at the units you can figure out what "math to do" AmpHours = amps x hours Amps = AmpHours/Hours hours cancel and you get just plain amps Hours = AmpHours/Amps amps cancel out and you get hours. The only other thing you need to realize if that AmpHours can be production, storage or usage and then just add or subtract as common sense would dictate and account for the inefficiencies in each process. AmpHours produced X 0.90 efficiency at storage = AmpHours stored Amps the circuit draws X hours you used the circuit = AmpHours consumed 30 AmpHours = 49.5 Amps X ? hours. Dividing both sides by 49.5 amps gives you; 30 AmpHours/49.5 Amps = ? hours = 0.606 hours = 36 minutes. (0.606 hoursX60 minutes/hour=36 minutes) This is assuming that you are not "using" any current to "run the boat" during that time. If you where running at night and using 3 amps to run the running lights and steaming light then 49.5 - 3 = 46.5 amps would be the denominator or 30/46.5 = 0.64hours or 39 minutes.
Batteries are only about 90% efficient at absorbing a charge so 55 X 0.90 = 49.5 AH is all you will get into your battery when your alternator is outputting 55 Amps for 1 hour. I find that for all this math stuff if you look at the units you can figure out what "math to do" AmpHours = amps x hours Amps = AmpHours/Hours hours cancel and you get just plain amps Hours = AmpHours/Amps amps cancel out and you get hours. The only other thing you need to realize if that AmpHours can be production, storage or usage and then just add or subtract as common sense would dictate and account for the inefficiencies in each process. AmpHours produced X 0.90 efficiency at storage = AmpHours stored Amps the circuit draws X hours you used the circuit = AmpHours consumed 30 AmpHours = 49.5 Amps X ? hours. Dividing both sides by 49.5 amps gives you; 30 AmpHours/49.5 Amps = ? hours = 0.606 hours = 36 minutes. (0.606 hoursX60 minutes/hour=36 minutes) This is assuming that you are not "using" any current to "run the boat" during that time. If you where running at night and using 3 amps to run the running lights and steaming light then 49.5 - 3 = 46.5 amps would be the denominator or 30/46.5 = 0.64hours or 39 minutes.
I disagree with Rick
All good points Rick but the concept of "cruisers only charge to 85% of battery capacity" ignores the fact that most have solar/wind generators and are at anchor 95% of the time. I for one leave my wind/solar charger on all the time. While I'm out on Bill and Alice beach scuba diving........ the batteries are charging. I ain't no math major but I can add and subtract. Most "cruisers" have figured out that the thing that limits there say besides $$$$ is fuel. Using fuel to charge the batteries is a really dumb given I have a wind/solar charger. I want my fuel to get me out of bad situations like weather or a tricky reef passage that would be hard given the tide and wind. I don't want to use it to charge my batteries unless I really need to. I'd suggest you look at a lot of boats that have been used to cruise in and look at the "upgrades" that folks have made to then. Besides the windvane "autopilot" (no electricity needed) and ground tackle (bigger is better) they have an almost universal preoccupation with electrical production means.
All good points Rick but the concept of "cruisers only charge to 85% of battery capacity" ignores the fact that most have solar/wind generators and are at anchor 95% of the time. I for one leave my wind/solar charger on all the time. While I'm out on Bill and Alice beach scuba diving........ the batteries are charging. I ain't no math major but I can add and subtract. Most "cruisers" have figured out that the thing that limits there say besides $$$$ is fuel. Using fuel to charge the batteries is a really dumb given I have a wind/solar charger. I want my fuel to get me out of bad situations like weather or a tricky reef passage that would be hard given the tide and wind. I don't want to use it to charge my batteries unless I really need to. I'd suggest you look at a lot of boats that have been used to cruise in and look at the "upgrades" that folks have made to then. Besides the windvane "autopilot" (no electricity needed) and ground tackle (bigger is better) they have an almost universal preoccupation with electrical production means.
Sorry Bill, you're not actually disagreeing at all
you just didn't read very carefully. Jared didn't ask about wind or solar charging, his question was about calculating charge times with his alternator alone so that was what I was responding to. If my post was misleading then perhaps I should have written, "Most cruisers without passive charging rarely charge their batteries to 100%..." FWIW, I do happen to know about passive charging as we've got a pair of Shell SM 110's on our boat. I'm perfectly aware that many full time cruisers use passive power generation and as you do, I highly recommend them for all the reasons you mention. However, for those who cruise that DON'T have wind or solar charging onboard (like a high percentage of the readers here I'll bet) Jared's question is germane and I'll stand by my point that THOSE boats charging by alternator alone only charge to roughly 85%. I am curious about your formula though. You cite a charge duration calculated on the alternator putting out a full 90% of it's capacity for the entire time. Are suggesting that the alternator puts out that amount of current to the battery for the entire charge cycle? I can assure you that's not the case on any of the boats I've been on, but perhaps I didn't read carefully enough
you just didn't read very carefully. Jared didn't ask about wind or solar charging, his question was about calculating charge times with his alternator alone so that was what I was responding to. If my post was misleading then perhaps I should have written, "Most cruisers without passive charging rarely charge their batteries to 100%..." FWIW, I do happen to know about passive charging as we've got a pair of Shell SM 110's on our boat. I'm perfectly aware that many full time cruisers use passive power generation and as you do, I highly recommend them for all the reasons you mention. However, for those who cruise that DON'T have wind or solar charging onboard (like a high percentage of the readers here I'll bet) Jared's question is germane and I'll stand by my point that THOSE boats charging by alternator alone only charge to roughly 85%. I am curious about your formula though. You cite a charge duration calculated on the alternator putting out a full 90% of it's capacity for the entire time. Are suggesting that the alternator puts out that amount of current to the battery for the entire charge cycle? I can assure you that's not the case on any of the boats I've been on, but perhaps I didn't read carefully enough
Hitachi Data
According to the Yanmar Service Manual for the 12V/55A alternator: Nominal output is 12V/55A; however, the rated output is 53A at 5,000 RPM. According to the graph the output curent (for a NEW unit) is: 0A @ 1000 RPM 32A @ 2000 RPM 47A @ 3000 RPM 52A @ 4000 RPM AND, the output is spec'ed at ONLY 20ºC. At normal engine room operating temperatures the output will be significantly less (as Rick mentioned in reply #2). The Manual doesn't provide output information for other than 20ºC. My guess (just a guess), is it would be reasonable to assume somewhere around 35AMPs max at operating temperature and also assuming a NEW unit. As the alternator ages it is normal for the output to further decreases (due to diodes, armature, etc.). Voltage: the graph shows the voltage spiking up rapidly to 14.5@ ~1700 RPM. It doesn't show the voltage running up to this RPM but it appears it would be 0V at around 1000 RPM - per the graph. In reality, though, it's probably sooner than that. Unfortunately, it doesn't really matter what the lower voltage and RPMs are because until the voltage exceeds battery voltage nothing will charge anyhow. Wear due to age: If the alternator is original on the 34, the 8D plus the start battery probably have nearly worn out that alternator by now (is it original?). That may be why the question is being asked. It's a tractor alternator for low electrical consumption and not meant to run a (house)boat. Siting on the hook and running the engine to charge the batteries will carbon up the engine and cause premature wear. Diesels like to be worked, not babied. Don't have the crank pully dia and alternator pully dia handy but according to the table it would probably take a good fast idle to reach anywhere near 4000 RPM for alternator. Hope this data helps.
According to the Yanmar Service Manual for the 12V/55A alternator: Nominal output is 12V/55A; however, the rated output is 53A at 5,000 RPM. According to the graph the output curent (for a NEW unit) is: 0A @ 1000 RPM 32A @ 2000 RPM 47A @ 3000 RPM 52A @ 4000 RPM AND, the output is spec'ed at ONLY 20ºC. At normal engine room operating temperatures the output will be significantly less (as Rick mentioned in reply #2). The Manual doesn't provide output information for other than 20ºC. My guess (just a guess), is it would be reasonable to assume somewhere around 35AMPs max at operating temperature and also assuming a NEW unit. As the alternator ages it is normal for the output to further decreases (due to diodes, armature, etc.). Voltage: the graph shows the voltage spiking up rapidly to 14.5@ ~1700 RPM. It doesn't show the voltage running up to this RPM but it appears it would be 0V at around 1000 RPM - per the graph. In reality, though, it's probably sooner than that. Unfortunately, it doesn't really matter what the lower voltage and RPMs are because until the voltage exceeds battery voltage nothing will charge anyhow. Wear due to age: If the alternator is original on the 34, the 8D plus the start battery probably have nearly worn out that alternator by now (is it original?). That may be why the question is being asked. It's a tractor alternator for low electrical consumption and not meant to run a (house)boat. Siting on the hook and running the engine to charge the batteries will carbon up the engine and cause premature wear. Diesels like to be worked, not babied. Don't have the crank pully dia and alternator pully dia handy but according to the table it would probably take a good fast idle to reach anywhere near 4000 RPM for alternator. Hope this data helps.
Fred, I like your tank setup.
Fuel is indeed freedom. I believe a boat should be equiped according to its intended use. For an offshore cruiser a wind generator and solar panels are the norm but for a coastal cruiser such equipment is not necessary. Beer, Ice and fuel are regularly available down the way. On overnight passages we recharge our batteries to 85% or 12.45 Volts give or take and that is enough. We carry a Honda 2000eu and at anchor it drives our 30amp three stage charger to replenish charge plus runs our air conditioner. When we sail to the Dry Tortugas we carry two five gallon cans on the rail for gasoline and a third one for diesel fuel. Refrigeration runs 24/7 off the house batteries. We are confortable, have cranking power and if we want to head into the wind have the fuel to do it. To the Bahamas we just carry gas for the dingui's outboard as fuel is available even in the outislands. To equip a coastal cruiser with wind generator and or solar panels for bay sailing or a few trips a year would be a waste of money. A few extra gallons of fuel will cover the needs.
Fuel is indeed freedom. I believe a boat should be equiped according to its intended use. For an offshore cruiser a wind generator and solar panels are the norm but for a coastal cruiser such equipment is not necessary. Beer, Ice and fuel are regularly available down the way. On overnight passages we recharge our batteries to 85% or 12.45 Volts give or take and that is enough. We carry a Honda 2000eu and at anchor it drives our 30amp three stage charger to replenish charge plus runs our air conditioner. When we sail to the Dry Tortugas we carry two five gallon cans on the rail for gasoline and a third one for diesel fuel. Refrigeration runs 24/7 off the house batteries. We are confortable, have cranking power and if we want to head into the wind have the fuel to do it. To the Bahamas we just carry gas for the dingui's outboard as fuel is available even in the outislands. To equip a coastal cruiser with wind generator and or solar panels for bay sailing or a few trips a year would be a waste of money. A few extra gallons of fuel will cover the needs.
Benny, sounds like you have a happy ship!
And John. Informative specs. You threw me with those high RPMs until I read the last part of your post. Back in the old days before my original alternator died during our Antigua flood, (it was a spare, stored in a flooded locker) I wired it up to a AutoMac. Remember those things? It had a rheostat to control/increase alternator output. I found that the stock 55amp Hitachi, put out it's full rated amperage just above an idle. Something like 15 to 1800 RPM. Then a short time later we replaced it with a Balmar so I didn't get to test it out too much. Anyway, its pulley is about 1/3 the size of the crank pulley so that dovetails perfectly with your chart.
And John. Informative specs. You threw me with those high RPMs until I read the last part of your post. Back in the old days before my original alternator died during our Antigua flood, (it was a spare, stored in a flooded locker) I wired it up to a AutoMac. Remember those things? It had a rheostat to control/increase alternator output. I found that the stock 55amp Hitachi, put out it's full rated amperage just above an idle. Something like 15 to 1800 RPM. Then a short time later we replaced it with a Balmar so I didn't get to test it out too much. Anyway, its pulley is about 1/3 the size of the crank pulley so that dovetails perfectly with your chart.
So for practical purposes...
Thanks for all that info. So, does this scenario sound practical? I don't need 100% charge on those batteries (85% charge for a week or so while out should be fine for us). I am interested in just not having to recharge at a marina every third day or so while out cruising the Chesapeake Bay. We normally never stay in one place on the hook more than 2 days. So if I start at 85% of charge and sail for a day and burn 30 Ah, then take off from our anchorage again the next day and run the engine at running speed for an hour or so on the way to the next anchorage, should we get that 47A (minus inefficiencies, etc.) to get us back up to the 85% of charge to avoid having to hook up to the power at a marina? I guess the better question was if we have that big 8D, a 55 amp Hitachi alternator, and burn 30Ah a day and motor an hour a day, can we just keep on trucking for a couple of weeks without hooking up to shore power? Thanks and sorry for the long winded question...
Thanks for all that info. So, does this scenario sound practical? I don't need 100% charge on those batteries (85% charge for a week or so while out should be fine for us). I am interested in just not having to recharge at a marina every third day or so while out cruising the Chesapeake Bay. We normally never stay in one place on the hook more than 2 days. So if I start at 85% of charge and sail for a day and burn 30 Ah, then take off from our anchorage again the next day and run the engine at running speed for an hour or so on the way to the next anchorage, should we get that 47A (minus inefficiencies, etc.) to get us back up to the 85% of charge to avoid having to hook up to the power at a marina? I guess the better question was if we have that big 8D, a 55 amp Hitachi alternator, and burn 30Ah a day and motor an hour a day, can we just keep on trucking for a couple of weeks without hooking up to shore power? Thanks and sorry for the long winded question...
Sounds like you'll be just fine
You'll figure most of this stuff out for yourself while you're out there which is way better than all this free advise you're getting from all us long-winded gas bags here on the BB But yeah, if you're only cruising on the hook for a week or two at a time and moving from place to place every few days I think you'll find the hour or two motoring in and out will get you back to 100% (or close.) Charging to 85% on the hook in between won't hurt your batteries a bit. I certainly wouldn't head for a marina just to recharge in a slip. Now, locating a really good tiki bar for excellent marguaritas, that's a different matter.... You'll be fine. Have fun.
You'll figure most of this stuff out for yourself while you're out there which is way better than all this free advise you're getting from all us long-winded gas bags here on the BB
But yeah, if you're only cruising on the hook for a week or two at a time and moving from place to place every few days I think you'll find the hour or two motoring in and out will get you back to 100% (or close.) Charging to 85% on the hook in between won't hurt your batteries a bit. I certainly wouldn't head for a marina just to recharge in a slip. Now, locating a really good tiki bar for excellent marguaritas, that's a different matter.... You'll be fine. Have fun.Thanks
Thanks. No "long-winded" answers bug me... I like them because it makes me read into things even more. You are right though - no better way to learn how much battery I have then to just use it for a week and run it dead (that is what that starter battery is for right). I guess I could buy one of those monitors, but I have plenty of other junk to replace first.
Thanks. No "long-winded" answers bug me... I like them because it makes me read into things even more. You are right though - no better way to learn how much battery I have then to just use it for a week and run it dead (that is what that starter battery is for right). I guess I could buy one of those monitors, but I have plenty of other junk to replace first.
At the risk
of telling you stuff you already know, if you don't have a monitor hopefully you at least have a digital voltmeter which will do fairly well in guesstimating your batteries state. I only say this because you made mention of 'run it dead' and that you don't actually want to do that, at least not literally. It's best to only run your batteries down to about 50% of their total capacity which would equate to about 11.9 - 12.0 volts with batteries at rest (no load on them.) Running them much lower than this WILL compromise the batteries health. Apologies if you already knew this. Fair winds and have fun!
of telling you stuff you already know, if you don't have a monitor hopefully you at least have a digital voltmeter which will do fairly well in guesstimating your batteries state. I only say this because you made mention of 'run it dead' and that you don't actually want to do that, at least not literally. It's best to only run your batteries down to about 50% of their total capacity which would equate to about 11.9 - 12.0 volts with batteries at rest (no load on them.) Running them much lower than this WILL compromise the batteries health. Apologies if you already knew this. Fair winds and have fun!
Bigger alternator?
Check with the Battery Shack in the keys. They wind their own on standard chasis. Not Balmar, but not as expensive either. You should be able to have an 80 or 100 amp alternator on 30 hp yanmar.... If you are worried about the take-off hp, external regulators let you shut off the alternator - making it free wheel, and not charge - if you ever need that extra power to fight a current. http://members.aol.com/captbr1/
Check with the Battery Shack in the keys. They wind their own on standard chasis. Not Balmar, but not as expensive either. You should be able to have an 80 or 100 amp alternator on 30 hp yanmar.... If you are worried about the take-off hp, external regulators let you shut off the alternator - making it free wheel, and not charge - if you ever need that extra power to fight a current. http://members.aol.com/captbr1/
Another inexpensive alternator
is the Hitashi (not hitachi) 90 amp from S/V Hotwire. See the link
is the Hitashi (not hitachi) 90 amp from S/V Hotwire. See the link
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