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Old 03-06-2010, 10:23   #16
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Originally Posted by john Fussell View Post
I hope what i write below helps even though it does not directly answer your questions.
If its working properly it will maybe do something like this...
The charger first bulk charges at 40a until the voltage is 29.25, it then enters absorbtion mode where it maintains 29.25v and gradually reduces the amps for a few hrs or until about 10a all that can be absorbed. It then enters float mode at 26.x volts.
The battery monitor should show this behaviour between volts and amps.
Does the charger have dip switch settings?

At anchor you will find the following problem...
40a charger is not enough. You need at least 100a.
When you run your generator at anchor you want to do it for the shortest period possible so you need the charger to put as many amps as possible into the battery. Imagine at anchor you start your generator and the 24v water heater is on, then this will draw 40a and so you will only have 60 left for charging the 440amphr bank. Thats why 100a is the minimum.

I have a 700a 24v battery bank, 7kw generator (cannot be heard from other boats) and 150a of 220v charging. The bank in the center of my 15m boat runs windlass and bowthruster and I have no spike type problems. Charging takes 40 mins a day at anchor if I stayed for a week. I can anchor 2-3 days without charging.
I used to have 80a of 220v charging and it meant the generator ran too long. I am now adding solar as well to make it even shorter.

I have no experience of what happens when you join 2 banks with 20 feet of cable... I think I would be inclined to leave them combined all the time but if I was leaving the boat for a few days or more I would probably seperate them. The only reason I say this is that paralleled banks drag each other down so I heard.
Hmm. A lot to think of here.

I am planning to upgrade the charger from the current 40 amp Newmar, but was hoping not to have to do it this year. I am aware of the generator run time issue but I had pretty much given up the idea of having an AC-powered battery charger that would make it possible to charge up with the generator in short runs. That would require more than 100 amps of charger and while that would not be too much for my 6.5kW generator, it is a very bulky, very expensive device, which besides not fitting in my engine room would overwhelm my shore power, which is 16 amps and already barely copes with the AC loads.

I had thought that 70 amps (like the Victron 24v 3000/70 Quattro) would be right -- will fit in my engine compartment and will more or less suit my shore power connection, and yet I can get some juice in the batteries with the generator in an hour run, if not a full charge.

I have a 110 amp brute of an alternator regulated by an Adverc which does an excellent job of getting the batteries to full charge any time I do any motoring, and usually the amount of motoring I do every day getting in or out of a port, even assuming perfect sailing, is plenty enough.

So I thought the 70 amp Victron would be enough. I don't have a DC water heater on board. We heat water with an Eberspaecher hydronic furnace, which doesn't draw all that much DC power, and with an AC immersion heater. During a generator run -- done typically during breakfast -- I will run the AC water heater, microwave, washing machine sometimes, power tools, and the gennie copes with all of those loads just fine, being like two shore power connections in capacity. I don't think I often have more than a 10 amp load going on the DC side, and usually much less than that, so that ought to leave at least 60 amps for charging, if not more.

Like yours, my generator (a lovely Kohler low-speed, 1500 rpm model in a sound enclosure inside my sound-insulated engine room) is barely audible on board (and bless it for that), and completely inaudible to other boats, so even long generator runs are not necessarily tragic.
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Old 03-06-2010, 10:30   #17
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Thanks for all that! One purpose of combining the banks using a switch for the time being was to be able to experiment to see whether the instruments are really bothered by the heavy gear or not. In case they are bothered, then I could just keep disconnecting them when I'm underway.

I can't do that until I'm sure that I won't be hurting anything, by charging the two banks through a splitter as if they were separate, despite the fact that the switch is on and they are combined. Is there any feedback through the splitter or any other kind of problem to expect from that, or can I leave the switch on and experiment away? Can you comment on that?...
I would NOT experiment. The type of damage caused by voltage spikes is often not seen immediately, and it is cumulative in sensitive solid state circuits. You might get away with it, but why try when you already have a solution, i.e., separate the banks when you're using the equipment?. Combine them when you're sitting at anchor or dockside.

You didn't mention how your charge your batteries at anchor. If, as the previous poster surmises, you're using an AC generator to power the Newmar battery charger, then you might want to think about a much larger capacity charger to cut down on generator engine time.

BTW, I agree with the notion that it could be a bad cell causing the Newmar charger to never reach the float stage. Will take some detective work to figure it out with all those batteries :-)

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Old 03-06-2010, 10:42   #18
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I would NOT experiment. The type of damage caused by voltage spikes is often not seen immediately, and it is cumulative in sensitive solid state circuits. You might get away with it, but why try when you already have a solution, i.e., separate the banks when you're using the equipment?. Combine them when you're sitting at anchor or dockside.

You didn't mention how your charge your batteries at anchor. If, as the previous poster surmises, you're using an AC generator to power the Newmar battery charger, then you might want to think about a much larger capacity charger to cut down on generator engine time.

BTW, I agree with the notion that it could be a bad cell causing the Newmar charger to never reach the float stage. Will take some detective work to figure it out with all those batteries :-)

Bill
OK, thanks for that advice, which sounds very sound to me.

I wrote about how I charge at anchor above. I'm planning to increase the AC charger but not enough to achieve full charges in short generator runs.

I'm actually not that dissatisfied even with the 40 amp Newmar. I don't expect a full charge, but I can get a good bit of juice in the batteries with an hour or so running during breakfast since we rarely go a day without running the main engine at least to get in or out of an anchorage. The way we cruise (presently), the big 110 amp alternator (with Adverc regulator) keeps up with the DC power consumption pretty well, and I consider that to be the primary charging device.
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Old 08-06-2010, 12:13   #19
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One question I'm still uncomfortable with; maybe someone of you has some idea:

If I am charging two banks through a splitter, and I accidentally leave those two banks combined and start up the main engine --

will there be feedback or some other kind of destructive phenomenon? Or will the splitter cope fine with charging two ends of a combined bank?

I don't possess the electrical engineering knowledge to give me any insight.

I have posed the question to Driftgate technical support and will let you guys know what they say. Meanwhile maybe someone has some idea?
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Old 08-06-2010, 14:35   #20
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Dockhead,
It won't hurt anything.
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Old 08-06-2010, 20:55   #21
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I did the same system on a halberg rassy, joined the hydraulic systems battery pack to the domestic to increase storage capacity.

Firstly the splitter will not be a problem, it merely parallels the batterys that have already been paralled by the switch. it will all be fine.

Secondly, electronic circuits are not affected cumlatively by voltage spikes, its not the way they work. The main problem with heavy loads on the DC supply is brownouts, ie large voltage drops, some early electronics some times got affected by this.

IN my eperience parallel them and try the thrusters with the electronics on. A lot of boats have thrusters and windlasses running from the domestic system with no problem, you are being over cautious.

I agree that the charger is a little underpowered for this large bank, but theres nothing wrong with it.

I also boiled a set of batteries, with a smart Mastervolt charger. Its nearly always related to the charger not exiting absorbsion mode, due to a contant DC draw or a cell fault. Despite claims to the contary lots of "smart" chargers dont seem to have a precautionary timer to protect against over long absorbsion periods. Really a smart charger should be told the capacity of the bank and set up protection timers to prevent over absorbsion charging periods. None to my knowledge do.
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Old 08-06-2010, 22:38   #22
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....

Secondly, electronic circuits are not affected cumlatively by voltage spikes, its not the way they work. The main problem with heavy loads on the DC supply is brownouts, ie large voltage drops, some early electronics some times got affected by this.
....
I also boiled a set of batteries, with a smart Mastervolt charger. Its nearly always related to the charger not exiting absorbsion mode, due to a contant DC draw or a cell fault. Despite claims to the contary lots of "smart" chargers dont seem to have a precautionary timer to protect against over long absorbsion periods. Really a smart charger should be told the capacity of the bank and set up protection timers to prevent over absorbsion charging periods. None to my knowledge do.
As a matter of fact, voltage spikes CAN and DO have a cumulative effect on solid state devices. There are tons of references to these effects and the phenomenon is well known in the electronics field. One example: MOV (metal oxide varistors) fail over time due to the cumulative effects of spikes they may be intended to clamp.

RE: absorption times, Victron chargers like the MultiPlus Inverter/Charger are fully programmable, including absorption voltage and maximum absorption time.

Bill
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Old 09-06-2010, 19:13   #23
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"corresponding to 14.675 volts in a 12 volt system. "
In a nominal 12VDC battery system, anything above 14.4 volts is considered to be excessive, detrimental, and the sign of a regulator failure.

I expect that means anything above 28.8 would similarly be something to be concerned with on a 24VDC system, although I'm not running out to check the numbers. And our 14.4 would be for active (i.e. bulk) charging--not just float charging. From 28.8 to 29.25...between meter accuracies (unless it is recently lab calibrated, 1% is too much to expect) and considering the rightmost digit often floats +-2 even in good meters....I'd suspect you are still hot charging, but then again, what is the battery voltage sensor hooked up to? WIth enough wire or a few voltage drops in either the sensor lead or the charging cables, maybe that's why you are seeing a paltry 0.45V in overcharge? Not a gross failure of anything, but just cabling problems with that mash-up?
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Old 09-06-2010, 20:58   #24
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"corresponding to 14.675 volts in a 12 volt system. "
In a nominal 12VDC battery system, anything above 14.4 volts is considered to be excessive, detrimental, and the sign of a regulator failure.

I expect that means anything above 28.8 would similarly be something to be concerned with on a 24VDC system, although I'm not running out to check the numbers. And our 14.4 would be for active (i.e. bulk) charging--not just float charging. From 28.8 to 29.25...between meter accuracies (unless it is recently lab calibrated, 1% is too much to expect) and considering the rightmost digit often floats +-2 even in good meters....I'd suspect you are still hot charging, but then again, what is the battery voltage sensor hooked up to? WIth enough wire or a few voltage drops in either the sensor lead or the charging cables, maybe that's why you are seeing a paltry 0.45V in overcharge? Not a gross failure of anything, but just cabling problems with that mash-up?
FWIW: Balmar's MC-624 Regulator takes deep cycle flooded & Optima spiral wound to 29.20v in bulk mode. I would bet other regulators do the same.
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Old 11-06-2010, 10:47   #25
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Well, I promised to report what the manufacturers of my Driftgage "X-Split" low-loss splitter said about this puzzle. Maybe it will be useful to someone.

They said that no harm would result from having the banks connected accidentally. The splitter will simply feed power equally into the two sides of the bank unless there is some difference of potential because of the long connecting wire, and this would cause no harm. No feedback or other problems; don't worry about it, they said.

SO that settles it -- I'm going to use the system like this for a while and see how it work out. Basically what I will do is leave the banks separated EXCEPT at anchor, when I will connect them so that the domestic loads can draw on both banks.

It will be a minor hassle switching the banks back and forth but I suppose not a big deal; we'll see.

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One detail which disturbs me is that my Victron battery monitor, which I just installed, cannot analyze the batteries since it has only one shunt, on the "domestic" bank. So it will not understand what is going on when the banks are conneted; it will not have measured the charge going into the "service bank", the loads coming out of the "service bank", or charge flowing between the two banks through the interconnection. Crap.

Anybody have any idea whether there is some kind of battery monitor that can totalize the information from two shunts? The only alternative would be to re-route the service loads to the "domestic" bank, which is a non-starter because (a) defeats the purpose of the interconnection; and (b) unacceptable long cable runs for the windlass and thruster. Crap!


Concerning overcharging: I'm just going to have to have someone look at it. I'll report what happens. Thanks for all the input.
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Old 11-06-2010, 18:31   #26
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Place your ground lead from the "Service" bank to the "Domestic" bank on the battery side of the shunt. Best to use a stud type of connector with the ground from the shunt coming in and the two grounds going out to the different battery banks.
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Old 11-06-2010, 19:02   #27
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Ugh, that last suggestion wont work, sorry.
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Old 12-06-2010, 08:49   #28
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Ugh, that last suggestion wont work, sorry.
Taking into consideration Kirchhoff first law, that the shunt is big enough to carry the current and can be wired into the negative and the following, why not?

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That's not applicable in this case because neither 24v bank is used for starting. The engine and generator each have their own completely separate 12v starting batteries each with its own separate 12v alternator.
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The way I wired them together is as follows. Since the banks are quite far apart from each other (about 20 feet at least, I would say), and to avoid extensive reconnecting of the various loads or reconfiguring the chargers and splitters, I simply ran a heavy cable between them with a heavy duty mechanical "on-off" switch. When I am at anchor, I join the banks by flipping the switch. When not at anchor, particularly when charging or motoring, the banks are disconnected and are charged and work the way they were originally designed.
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Old 22-06-2010, 14:33   #29
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"corresponding to 14.675 volts in a 12 volt system. "
In a nominal 12VDC battery system, anything above 14.4 volts is considered to be excessive, detrimental, and the sign of a regulator failure.

I expect that means anything above 28.8 would similarly be something to be concerned with on a 24VDC system, although I'm not running out to check the numbers. And our 14.4 would be for active (i.e. bulk) charging--not just float charging. From 28.8 to 29.25...between meter accuracies (unless it is recently lab calibrated, 1% is too much to expect) and considering the rightmost digit often floats +-2 even in good meters....I'd suspect you are still hot charging, but then again, what is the battery voltage sensor hooked up to? WIth enough wire or a few voltage drops in either the sensor lead or the charging cables, maybe that's why you are seeing a paltry 0.45V in overcharge? Not a gross failure of anything, but just cabling problems with that mash-up?
OK, I've been back on the boat and there is definitely something wacky with the charger.

When I got there, the charger had been left off and the batteries were down. I switched on the charger, and everything worked the way it was supposed to. A few hours of bulk charging, at 29.25 V for a short time then 28.25 V. Then into float at 26.88 V, just as it should.

But then on the second day, I cranked up the engine and ran it for about half an hour. That night, I smelled battery acid (one of the banks is under my bunk), and sure enough, although the batteries have been connected to shore power for a day and a half by this time, showing 100% charge on the Victron battery monitor, the charger is pumping in 34 amps (!) at 28.25 volts, for God knows what reason. This was in the middle of the night with almost no loads on, other than refrigeration.

WTF?

Is it just a case of a shot charger, or is it somehow related to running the engine? I confess that I forgot to switch off the charger before cranking up the engine, but the charger manual does say there is no harm in this.

What in the world could it be?
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Old 22-06-2010, 15:45   #30
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When I got there, the charger had been left off and the batteries were down.
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showing 100% charge on the Victron battery monitor, the charger is pumping in 34 amps (!) at 28.25 volts, for God knows what reason. What in the world could it be?
Perhaps one duff cell in one of the batteries, which because they are now all wired together .................

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