Darn AGM Batteries

[Maine Sail]

Sorry for the delay I had not had a chance to draw this out until now..

Here's how to keep the wonderful safety features of the 1/2/BOTH/OFF most boats already have and you can simply add one more ON/OFF and have both a dedicated start battery and complete redundancy..

1 - If the starting battery goes bad simply turn the 1/2/BOTH/OFF to BOTH and flip the ON/OFF to OFF you can now start your engien and do house loads off the house bank yet still 100% isolate the starting battery.

2 - If the House bank goes bad simply flip to position #2 and leave the ON/OFF turned to ON. This will allow powering house and starting loads from the starting battery and allows it to also act as a reserve.

3 - For normal everyday use flip the 1/2/BOTH/OFF to #1 and the ON/OFF to ON..

While a tad more "complicated" than a single ON/OFF, you have two ON's and two OFF's to do it is still very easy compared to most boating things. In an emergency you still retain all the flexibility and isolation you'd want or need.

 

[tommays]

Mainsail

Thanks for taking the time to make the drawing that does seem to cover all

 

[Maine Sail]

\
Guy's,
There was a catastrophic failure of the house bank, most likely an internal short as they would not take a charge or hold one. When the start bank was "combined", the ONLY easy option to get power on-board with the DCP, so he could use the VHF, it whacked the start battery enough to also kill it.

On center console fishing boats with equally sized banks jump starting via "combine" can be fine. But when you have an 800Ah house bank and a group 24 starter if you kill that house bank and need to "combine" you are really going to be taxing the capabilities of the starter battery. In a situation with "unequal banks" I much prefer to isolate the dead battery and switch entirely to the 100% SOC fresh battery without using the BOTH or COMBINE feature.

Here's a way to look at it.

You have a new milk shake with one straw. That one straw and the person sucking on it get the entire milk shake.

You now have the same milk shake but now have TWO straws and Rosie O'donnell is on the other straw... How much milk shake you gonna get?? Enough to get full?? Enough "straw" to start the engine...??

Why have two "loads" (engine and dead bank) sucking on the same milk shake when you don't need to...?

I had it happen to me this summer. A customer killed his banks by not knowing his alternator was not working. Because he was "charging", or thought he was, on BOTH, he killed both banks.

When I went out there to fix it I bought my jumper pack. Not paying enough attention I connected it to the larger house bank and tried to start the motor. Click, click. The jumper pack did not have enough in it to be getting sucked on by the mammoth house bank (straw #1) and to start the motor (straw #2). I did a head "boing" Doh' and came back the next day and connected it to the group 24 starter battery and the motor fired up no problem...

The DCP can be fine for certain applications I just don't prefer them to other systems that can leave you with more options, more flexibility and achieve a similar outcome unless you add two ON/OFF's to it..

Adding a DCP to fix the problem of routinely killing a house bank is a placebo not a cure.

 

[Maine Sail]

Great reply. I agree 100%. I think the concept of the DCP switch does work, as you say, for those with say twin engines or two equal battery banks, even though many of us have moved away from that concept.

Wired in stock form they work well for what they were designed for, fishing boats or boats with close to equal sized banks. You still do give up isolation & redundancy but some folks are willing to take that gamble for the "simplicity" of an ON/OFF.

It is not until you've had a catastrophic bank failure, or seen a few examples where the lack of bank isolation or bank redundancy can be detrimental, that you would think they are anything but the greatest thing since sliced bread..

I have had at length discussions with Blue Sea engineers as to the origins of this design, it was to prevent voltage drop outs for guys starting the motor many times per day to move to different fishing grounds so they would not "re-set" their electronics. Though it is now being installed in deep cycle applications on cruising boats, that was not the original intent..

They have since made some changes to the instructions noting that with unequal banks the alt should feed the larger bank first to prevent relay cycling.

 

[Maine Sail]

Two minor concerns I have with your preferred battery set up (mine is similar).

It is not really a "preferred" system. Just one of MANY options and seeing as most all boats came with a 1/BOTH/2/OFF why not show folks a bunch of ways to use it...

As I mentioned in the post, if you want the utmost in bank isolation then you keep the alt on the "C" post of the 1/BOTH/2/OFF and use it as a "use" and "charge directing" switch. The only time you could not do this is if you had an Echo type charger.

1. What do you do if one of the batteries in your house bank goes bad considering that all the charging goes directly to that bank? I suppose you can instantly switch to running on the start bank or battery, but it won't be getting any charging, while the bank with the bad battery will continue to receive a pretty big charge from the engine, solar, wind, what have you. This has happened to me offshore on a long motoring run when one battery shorted out (only about a year old) and suddenly became blazing hot. I had to basically disconnect everything and wait for things to cool down before I could reconfigure the battery banks temporarily so that I could use the engine and get a charge into the remaining good batteries. Luckily it was fairly calm or it could have been a very difficult job offshore.

For me this fix is quite easy. When I say "direct to the house bank" it does not necessarily mean the + post of the battery itself. I run everything to a bank of fuses first or a pos buss. So all I need to do in the event of a shorted bank is to remove the house bank neg, 15 seconds with a wrench, and turn the 1/BOTH/2/OFF to BOTH. Now the house is off line and the alt current flows directly to the start battery via BOTH. Disconnecting the banks neg lead is often far easier than the + connections.

If you follow the DCP diagram in the original post you can see that by simply turning off one ON/OFF switch you've not lost charging. This is the beauty of a DCP plus two out-of-sight ON/OFF switches but again this config gets more expensive than simply adding an ON/OFF to a 1/2/BOTH..

2. Is it possible to get a short in the alternator such that you have a major problem but short of blowing the 150 amp fuse I have in the line? Not having a cutoff switch in that line makes me slightly nervous.

Alternators are "self limiting" thus if your wire is sized to handle the full output of the alt the alternator has no way to melt it down. They can't supply current when there is no load so you'd need a battery bank there to accept the full output anyway.

I generally suggest a "service switch" when the alt is direct wired. This can be in the form of a lever arm breaker or an ON/OFF switch. This way you shut the alt down when you're working on the engine to avoid wrench shorts...

 

[Kettlewell]

Stu, my thought was that with all the charging sources going direct to the house bank you don't have an easy way to shift them over to the start or reserve bank if for some reason the house bank goes south. With the old 1,2, Both switch traditional arrangement you were switching both the charging sources and the draw to whichever position the switch was in, so if for some reason your house bank was unuseable (shorted battery) with the flick of a switch you were running on bank 2: charging, energy draw, everything.

 

[Argyle38]

Couple of questions for MainSail. On the original post, you mention lifetime based on recharging and equalizing. Isn't the depth of the discharge in the first place an important variable?

Second, in the above sketch. Where would you put the alternator? Attach it directly to the starting battery with an ACR connection to the house bank?

 

[Maine Sail]

Couple of questions for MainSail. On the original post, you mention lifetime based on recharging and equalizing. Isn't the depth of the discharge in the first place an important variable?

Those statements are directly from Lifeline battery. They ASSUME you are not discharging below 50%. Obviously the shallower the discharges the longer life you'll get, but with AGM especially, recharging them to full, as OFTEN as possible, is critically important..

Second, in the above sketch. Where would you put the alternator? Attach it directly to the starting battery with an ACR connection to the house bank?

Preferably the house bank. You could use the "C" post but now you have two of options for load disconnect/frying the alt diodes, as opposed to just one.

 

[wufibugs]

Main, for who are electrically challenged, or just plain challenged, a down-and-dirty ideal wiring diagram for the 1/2/both/off and the on/off? I too have a pair of Lifeline AGMs for the house and another one to start and had not known they were to be equalized. Guess I'll have to re-read that section of my old 2000 inverter/charger manual.

 

[Argyle38]

Those statements are directly from Lifeline battery. They ASSUME you are not discharging below 50%. Obviously the shallower the discharges the longer life you'll get, but with AGM especially, recharging them to full, as OFTEN as possible, is critically important..



Preferably the house bank. You could use the "C" post but now you have two of options for load disconnect/frying the alt diodes, as opposed to just one.

Well, that is disconcerting. I've had mine four years. Four house for 440 AH and a Group 27 for cranking. I've had them for four years. First year was on the hard, plugged into a smart charger and being charged most of the time. Second year was at a dock, also plugged in and charging most of the time. The past two years I've been on a mooring and the batteries definitely more use and less charging. Still I try to charge as much as possible, but don't yet have solar or wind power (solar planned for this spring). So far so good though. A check on the voltage last week shows they're holding charge pretty well over the winter. I suspect, however, that I'll be changing them out before I had initially planned.

The whole reason I went with AGMs was for being on a mooring. AGM's hold their charge better when not in use and can take more current, which seems better for charging with a diesel. It sounds like those advantages are offset by the fact that you have to run your engine that much longer to get the last 5% of charge, which takes quite some time. And that is before you take into account the increased cost.

I also have the Dual Circuit plus, hence my interest in this thread . I didn't view the switch as anything really special, just a DPDT switch with an option to short the parallel circuits. I have one circuit connecting the house battery to the alternator and the other circuit connecting the starting battery to the to the starting circuit. The starting battery is connected to the alternator through an ACR. Not sure why I didn't just hard connect those, perhaps I was worried about transients damaging the alternator regulator during cranking, don't remember though . This system works ok for me, but as has been mentioned here, I do not have the ability to isolate separate battery banks for running house loads, not without a wrench anyway. If I were to ever re-wire, I'd probably include that ability, but I don't think it's worth for replacing what I have.

Great write up. Interesting stuff.

 

[Kettlewell]

I'm not down as much as MaineSail and Stu on the Dual Circuit Plus design, because its limitations are way down my list of situations I have had to deal with. I like the fact that with one setting both the house bank and the starter bank are turned on, yet isolated. Assuming the alternator and solar etc. charging sources go direct to the house bank, and if there is an EchoCharge or a combiner between the banks taking care of keeping both banks topped up, you've got a good set up for 98% of the time. The most likely battery failure scenario I have encountered is running the house bank down too far and not being able to start the engine. That is taken care of with the DCP. I can't ever recall running down my dedicated starting battery so far I needed to start on the house bank because nothing else runs off the start battery. The emergency parallel setting would take care of the situation if your EchoCharge died--just start the engine and wait a few minutes, then switch to the parallel setting and still be able to charge both banks manually. Now I think you're up over 99% of common situations met onboard. The one situation it doesn't cure is when one or more batteries just die for some reason and you have to cut them out of use and run on whatever batteries are left, but that usually requires shifting batteries and/or cables around anyway in order to cut the bad battery out. If you set up your battery compartment carefully you can make it so that in just a few minutes you could move the cable to run just off the house bank, or just off the starter bank, if needed. I did once have one of three batteries in my house bank short out while offshore, necessitating me to disconnect it and let everything cool down while running my GPS on the start battery. That is the one situation that I could see where the DCP isn't ideal, but every set up has its disadvantages and advantages. I have meant to make up a short jumper cable or two that could be used in situations like that for quick rewiring, but in real-world situations I have been in the time to move cables was very short, even offshore. I do try to keep appropriate tools handy. You have to decide for yourself which ones are important to you, based on your own experiences and those of others.

 

[Maine Sail]

I'm not down as much as MaineSail and Stu on the Dual Circuit Plus design, because its limitations are way down my list of situations I have had to deal with. (snip) I did once have one of three batteries in my house bank short out while offshore, necessitating me to disconnect it and let everything cool down while running my GPS on the start battery. That is the one situation that I could see where the DCP isn't ideal, but every set up has its disadvantages and advantages.

Interesting that you've been in the 1%....

While rare these situations do happen and they don't need to be a complete bank failure to cause issues.

For isolation of starting / house I like a 1/2/BOTH with a ON/OFF added (when cost is a focus) or three ON/OFF switches with the the "combine" switch wired properly to the load side of the start and house ON/OFF's or the DCP with two ON/OFF switches.....

Most times, about 8 out of 10, when I come across the 3 ON/OFF method, they are incorrectly wired leaving you no bank isolation capability, just "combine".....

The DCP is not a terrible device and when wired with two more ON/OFF's it is a really good switch, but I have personally had a number of instances where it has stung customers of mine when wired in stock form.

As long as folks understand what they have given up, and know how to work around those rare but very potential issues, then why not....

For folks who UNDERSTAND their system and COULD go in and disconnect a failed bank then the DCP can be fine. The one problem I have with it is that they are very often used by boaters who would not know how to do effect those repairs and less by boaters who could...

 

[Kettlewell]

No matter what set up you have there is a failure mode, and it is sure to be discovered, usually at 2 AM on a black night when the anchor is dragging. As I said in another thread, I believe we tend to overthink these things trying to cover all possibilities, making the system more complicated. This can lead to both operator error and equipment failures in different scenarios than we ever imagined. Your example of the failure situation with the DCP sounds like a pretty unusual situation. I would suggest instead everyone should have at least one (I carry several) battery powered handheld VHF radios, a small battery powered GPS unit, and paper charts so that you are never without these essentials even if all power goes down. When the house bank went dead he should have been able to start it on the waiting start bank. That's why I advocate a dedicated starting battery that does nothing else.

One other thing is that one person's "intuitive" system is another person's non-intuitive--I see this all the time on other people's boats. They are showing me proudly how they have set up something to be just the way they want it, and I'm thinking to myself "what an idiot." Then when I row away he is thinking to himself "that guy is such a dummie--he does everything wrong on his boat!"

 

[Stu Jackson]

Stu, my thought was that with all the charging sources going direct to the house bank you don't have an easy way to shift them over to the start or reserve bank if for some reason the house bank goes south. With the old 1,2, Both switch traditional arrangement you were switching both the charging sources and the draw to whichever position the switch was in, so if for some reason your house bank was unuseable (shorted battery) with the flick of a switch you were running on bank 2: charging, energy draw, everything.

Old as in IF the switch was being used for BOTH (pi) charging and use. Once the AO is removed from the C post and it goes to the house bank, MS then answered the question. Simple.

 

[Kettlewell]

Old as in IF the switch was being used for BOTH (pi) charging and use. Once the AO is removed from the C post and it goes to the house bank, MS then answered the question. Simple.

If all the charging sources are connected directly to Bank #1, and then something goes wrong with Bank#1 so you can't use it, you lose all the charging sources when you switch to Bank#2. You can't run an EchoCharge or a combiner from dead Bank #1 to good Bank #2. You would have to move some wiring around to hook up the alternator to feed Bank #2.

And, yes MS has answered this question well with some of his earlier posts:

For me this fix is quite easy. When I say "direct to the house bank" it does not necessarily mean the + post of the battery itself. I run everything to a bank of fuses first or a pos buss. So all I need to do in the event of a shorted bank is to remove the house bank neg, 15 seconds with a wrench, and turn the 1/BOTH/2/OFF to BOTH. Now the house is off line and the alt current flows directly to the start battery via BOTH. Disconnecting the banks neg lead is often far easier than the + connections.

and

As I mentioned in the post, if you want the utmost in bank isolation then you keep the alt on the "C" post of the 1/BOTH/2/OFF and use it as a "use" and "charge directing" switch. The only time you could not do this is if you had an Echo type charger.

 

[StephenD]

Wow, what a trove of great ideas! I'm one of the "dummies" that installed the DCP product and I'm happy I did. I realized it's limitations but accepted those as a good tradeoff for the convenience. I have to give a nod to the most well considered solution for battery connections: Don Casey's chapter on the issue. It took me through the evolution of thinking about alternator connections, combiner relays, and charging strategies. What an education!
His ultimate solution (as mentioned above) is wiring the house and start side isolated from one another, each with it's own on/off switch. The addition of one more on/off switch to combine both sides allows the most flexible and powerful solution because you can now use either one or both battery banks to run either the start, or the house, or both. Adding a smart combiner makes forgetting to charge the batteries a thing of the past.
Three on/off switches is about $75. (You could get 2 black ones and a red for emergency combine) A combiner relay about $55, that's $130 for everything.
For me I am going to get two on/off switches to isolate the 2 banks, but love the ease of flipping just one switch when departing or returning to my slip, not to mention not having to explain what to do when guests want to help me.

 

[SG]

I've had four sets of AGM's on our boat over 18 years of use (since 1998). The main bank has just under 800 AH; and there are separate engine and generator start batteries. I had, for for about 9 years a Heart 2500 130 Amp rated charger/inverter and voltage regulator/controller package.

We also have a 250 AMP ALternator and Balmar smart regulator. (In addition there's is a separate 50 Amp alternator which just charges the engine start battery.)

We changed "up" to a Mastervolt 200 Amp / Combi unit and system. We've always had thermal compensation and monitoring on the battery banks to keep from frying them in very hot weather -- and to allow for more aggressive charging when it's colder.

I charge the batteries FULLY almost every time I discharge them more than 80% (usually every day). I'm very attentive to charging voltages AT the batteries. The guidelines are not for what's the voltage at panel -- but what you're delivering in volts and amps at the batteries. When our four chart plotter displays (2 in the cockpit, 2 at the nav station), our PC at the Nav Station, instruments, refrigeration, etc. are running -- we can be drawing 40-50 amps. So if we're putting-out 130 Amps out of the generator through the Combi charger, not all that much is going to the House Bank to replenish loads as one would think.

The first AGM's lasted 7 years -- they would have lasted longer, but because of our cruising plans "they didn't owe us anything". The next set lasted 4 years. The next 3 years. The next 1.5 years. I'm into the replacement bank of Lifelines for the second year now.

I've adjusted the voltage and duration of Bulk/Absorption/upward to reflect what the BATTERIES actually see while we're sailing. I hope this has the effect of extending the life of the batteries. I frankly don't know what the longevity issues are. The batteries should last longer. The last set was supposedly badly sulfated. They wouldn't hold a charge.

LIFELINE STOOD BEHIND THEIR PRODUCT! They suggested that we weren't being aggressive enough with the recharging. I've adjusted that upward. They suggested occasional equalization -- I've done that twice since getting the batteries at the being of the last season.