Battery question

[John]

We have two 12 V AGM batteries on our boat (C36). I feel that this is not enough for doing any sort of extended trip - even a couple of days - especially not if we run the refrigerator, since I don't have solar or a wind generator (yet). So I'm considering installing a third battery. What I'm not sure of is what sort of set-up to use. My thought is to isolate it from the other two and use it for starting the engine only. Then the other two would be for the house bank.

Does this sound like the best approach? If so, should I get another AGM battery, or can I use something else? Also, I haven't the foggiest idea about how to go about wiring something like that. Does anybody have any suggestions as to where to find a schematic for this?

Or would it be better to wire up this battery with one of the existing ones (e.g. the "number 1" battery) and use this for the house bank? In that case, I assume I would have to get another AGM battery. Would I wire it parallel or in series?

Any other suggestions or ideas? Thanks.

 

[jviss]

Get some help

Based on your question, I assume you really don't know much about this topic; I recommend you get a local knowledgeable person to help, just so no one gets injured.

Two batteries of at least 75AH, if in good condition, with a good charging system, are sufficient for cruising with a fridge, assuming it's something like an A-B, drawing about 5 Amps on a 50% or less duty cycle. I have done this. Start your trip with several blocks of ice in the bottom of the fridge, and fill the fridge - once everything is cold it will be easier to maintain the temp than to attempt the same with a fridge full of mostly air. We even fill empty spaces in our too-big fridge with gallon jugs of water.

Adding a starting battery will not affect your cruising capacity. Starting a small marine diesel requires remarkably little electrical power (with a relatively large current only momentarily; for example, 20A of glow plug current for 15 seconds, then 60 or more Amps starter current for a couple of seconds).

If you add house capacity, since they new battery or batteries are not the same age as the existing ones, they shouldn't be combined as a single bank. If you want to add capacity, I recommend adding two more, and arranging them all as two separate house banks, and using them alternately (bank one on odd days, bank 2 on even days, for example).

Combining batteries is done in parallel. That's just the tip of the iceberg, though. You really should know about proper wire gauges, and proper yacht wiring practice, including attaching terminals, using bus bars when called for, wiring switches, wiring the alternator charging wire, distances of batteries to circuit panels and potential fusing requirements, and so on.

Make sure you can fully charge the bank. We charged every day for about two hours to top off our two 75AH flooded cell batteries. We ran an A-B fridge, incandescent cabin lights, anchor light, radios, etc.

Might want to consider investing in LED replacement bulbs, especially anchor light.

 

[Rob]

Books on DC

John - I would recommend getting one of the many great books out there on DC systems for sailboats. Nigel Calder has a great one that covers everything you need to know. Even if you get the job done by a marine shop or marine electrician - its helps tremendously to understand the system yourself and know how to best maintain it over time ensuring the full life expectancy on each battery.

- Rob

 

[Stu Jackson]

An energy budget is a requirement

Here's one for you to use. jviss nailed it with a perfect description. We should keep that one and copy and paste it for John's questions, which recur frequently. I agree with Rob's suggestion, great sources. John, I'd be more than glad to come over one day and walk you through all this - most of us learned the hard way: we had to read all the danged books!

 

[John]

Stu

Stu,

Anytime you are free, please give me a call. My electric system is not so weak that I can't keep beer cold!

I've done a little bit of wiring on the boat, including installation of a propane leak detector system and of a radar, but I know I still have a loooong ways to go. I've started reading "The 12 Volt Bible for Boats", which is somewhat helpful, but I will also look for that Calder book.

 

[seadaddler]

C-36 Forum

All great info mentioned here to help you.
Try going on the C-36 website for owners of your
boat that have done many upgrades.
Some one here can help with web site.
Nick

 

[Landsend]

you are correct in being low on battery capacity...

the fridge is the big draw...how about finding room for two deep cycle golf cart batteries and buying a battery combiner?

 

[Landsend]

You most likely need a larger alternator also

nm

 

[Stu Jackson]

John, check your email

for separate info input

 

[Maine Sail]

John,

You're in very good hands with Stu! He'll take care of you...

One thing to consider, if you have not already, is a battery monitor. It is the frst thing I recommend to folks wanting to increase alternator size or battery bank size. An energy budget is a good start but they are far from accurate. A half hour more a day of this and an hour more of that and you're bordering on an inaccurate budget.

Others have mentioned most of the important points but a battery monitor is honestly SHORT money in the big scheme of things. It is the one item on my boat that has actually saved me money by allowing me to take better care of my batteries. Properly set up they will tell you when you are at exactly 50% of charge and need to re-charge. They will also accurately tell you exactly how much each component draws and exactly how much you consume in 24 hours. When I got my first battery monitor my idea of state of charge, even with an energy budget, was way out of whack with where I really was. Things like auto-pilot and the stereo are variable draws meaning they are not always constant.

For example using a 50% cycle time for your C-36 fridge may not be very close to accurate. On my 1987 C-36 my cycle time, after it had been on for two full days and was fully chilled, was still almost 70% because Catalina did a poor job of insulating it. On my 2005 C-310 (same builder) cycle time was closer to 55% unless we used the lower fridge door instead of the top access then it bumped closer to 60% as the cold air fell out of the door every time we opened it. What I'm getting at is that your fridge can be very variable too. The first day you fire it up you may be close to 80% cycle time but after cool it could be 50%.

Batteries, cables and the odds and ends to add one are expensive and may not even be totally necessary. The only way to know accurately is to use a battery monitor and measure your average daily consumption over a few day or week period.

Their are two battery monitors that have great reputations and that are very reliable and they are the Link 10 and the Xantrex XBM. You may find after adding one that you don't need anotehr battery or even a bigger alternator.

Unfortunately for me I upgraded three boats with bigger alternators before I bought my first link ten. Since buying a battery monitor I have yet to see any of my alternators put out more than 40 amps for more than a few minutes. In many cases, at a 50% discharge, there really is no need for a HUGE 100 amp alternator unless you are feeding a HUGE bank. I spent lots of money buying beigger alternators before I got smart and spent the $200.00 on a monitor that told me I never needed one.

My current boat was a full time live-a-board cruiser for five years. She has only 240 amp hours of house bank, a stock 55 amp alternator and an 80 watt solar panel and even on the hook 7 days a week for five years she was sufficient in her current set up. You may need more batt capacity because my refrigeration is engine driven but a batt monitor will tell you for sure..

Really they are short money in the whole scheme of things. Measuring battery state of charge by voltage is very tough when you are actively on the boat as the batteries must sit for a few hours, with zero draw, to get an accurate reading..

Consider adding a battery monitor first and it may save you money...

 

[John]

Problem solved

I was just at a used marine supply store and picked up a folding solar panel - 6.5 watts - for $40. So I don't have any worries any longer.

Just joking, of course. I'm looking forward to going over this issue with Stu whenever he has time, and of course I hugely appreciate his willingness to help as well as the suggestions of everybody else here.

Maine Sail's suggestion of getting a battery monitor sounds like a good one, but I think I'll wait till I read up a little more so that I have a better understanding of exactly what the monitor is showing.

 

[jviss]

Yes, but...

Maine,

I respect you views and your experience, but about the large alternator issue. You don't need a huge house bank to need a big alternator. Many experts recommend charging flooded lead-acid batteries at 1/3 capacity (1/3C) during the bulk phase. This not only gives you quick charging, but is apparently better for the batteries. At 240AH of capacity, 1/3C is 80 Amps. Mine is a 300 AH house total, so 100A. If you never see more than 40A its because your regulator isn't providing enough field current to your alternator to do it, or your alternator isn't capable of it.

I have an accurate DC current clamp meter, and I can see 100A at the start of charging. I'm not happy that my "smart" regulator won't keep it up for the duration of the bulk phase, but I guess it's not really that smart. Bulk should be 1/3C until the bank voltage reaches your absorption voltage level (usually a set point, as it varies with battery chemistry and temperature); mine is set at 14.4. At this point, you are at approximately the 75% point of state of charge. On my regulator, the absorption phase is timed, and when it times out it goes to float, at 13.6V. I would prefer it stay in absorption until the current at 14.4 V equals 2% of capacity, or 6A in my case, which would be fully charged.

That said, I wish I had a Link10! my big issue is diminishing capacity of the bank because I never do an equalization charge.

Anyway, sorry for the rambling response. My point is that a properly sized alternator (usually larger than 55A for increased house banks) is a good, for faster charging and battery health.

In addition, I caution against trusting that smart regulators are that smart. Note that there is usually no way of telling them the size of the bank being charged, or the capacity of the alternator; nor is there usually a charge current probe. There certainly should be a remote voltage sense lead, and battery and alternator temperature sensors.

 

[jviss]

Comment on alternator sizes

You don't need a huge house bank to need a big alternator. Many experts recommend charging flooded lead-acid batteries at 1/3 capacity (1/3C) during the bulk phase. This not only gives you quick charging, but is apparently better for the batteries. At 240AH of capacity, 1/3C is 80 Amps. Mine is a 300 AH house total, so 100A. If you never see more than 40A its because your regulator isn't providing enough field current to your alternator to do it, or your alternator isn't capable of it.

I have an accurate DC current clamp meter, and I can see 100A at the start of charging. I'm not happy that my "smart" regulator won't keep it up for the duration of the bulk phase, but I guess it's not really that smart. Bulk should be 1/3C until the bank voltage reaches your absorption voltage level (usually a set point, as it varies with battery chemistry and temperature); mine is set at 14.4. At this point, you are at approximately the 75% point of state of charge. On my regulator, the absorption phase is timed, and when it times out it goes to float, at 13.6V. I would prefer it stay in absorption until the current at 14.4 V equals 2% of capacity, or 6A in my case, which would be fully charged.

That said, I wish I had a Link10! However, my big issue is diminishing capacity of the bank because I almost never do an equalization charge.

Anyway, sorry for the rambling response. My point is that a properly sized alternator (usually larger than 55A for increased house banks) is a good, for faster charging and battery health.

In addition, I caution against trusting that smart regulators are that smart. Note that there is usually no way of telling them the size of the bank being charged, or the capacity of the alternator; nor is there usually a charge current probe. There certainly should be a remote voltage sense lead, and battery and alternator temperature sensors.

 

[Maine Sail]

Jviss..

I had a Balmar ARS-5 set up properly with the temp sensor and a 90 amp alt. The batteries will only accept what they will accept and the smart regulator can only force as much as it can force until the temp get to hot. Sure I would see a brief spike up to about 70 amps when I fired it up but it ramped down rather fast as the batts would not accept it. Forcing to much in can be as devastating to a battery as under charging or running it dead often..

 

[jviss]

OK

Just so I understand, it was servo-ing back because of the battery temperature? I only ask because I think it would be hard to know if this is what is limiting the current, unless there's an indicator on the regulator that shows it has reached a thermal limit. My comment in the regulators is that since they don't know the bank size, and you apparently can't program them for bulk charging rates, they are set up very simply to perform conservatively.

Doesn't matter, there doesn't seem to be an alternative available at the moment.

What engine speed do you charge at?

 

[Maine Sail]

Batteries

Jviss,

Batteries will only accept what they will accept at certain points of charge. At near dead they can accept most all the alt can give but as they fill up they do not let the alt force feed them more than they can handle. Just because you have a 100 amp alternator or charger does not mean your batts will accept it all because it's dependent on the state of charge.

My ARS-5 never went off on temp and after lengthy conversation with Balmar they explained to me that it was working properly. As I get closer to full charge my alt would put out as little as 2-4 amps per hour because that is all the batteries would take. That's why the last ten percent of charge always takes the longest because the least is being accepted. Getting back to 90% goes fairly fast from 50% but the last ten takes hours and hours of run time. This behavior is normal.

 

[jviss]

I understand

Maine,

I'm not arguing, and I understand battery charging; I'm an electrical engineer. I was specifically referring to the way most designers break this into three distinct charging phases, bulk, absorption, and float; and what the charging profile looks like during bulk. Bulk is usually defined as constant-current phase, i.e., the current is the independent variable, and the voltage is monitored such that when i reaches a particular set-point, nominally 14.4V for flooded batts, the absorption phase is entered. During the bulk phase it is desirable to see a constant current of as much as 33% of C; if no battery temp sensors, you would lower this to 20%, which will not cause overheating.

Many boaters don't see max bulk current simply because they are not turing the alternator fast enough.

In absorption, you charge at constant voltage; this is where you will see current gradually decline as the battery charges.

I hear you, but I can't parse "batteries will only accept what they will accept" (probably because it is a tautology). Batteries in good condition will take high, constant current when in a low state of charge, and when they achieve a higher state will warm up. At nominally 14.4V and I=.33C, they will be about 75%, which is time to hold that voltage - more specifically, to regulate to 14.4, which will require decreased current as charge builds. That is, change from constant current to voltage regulated charging. When I reaches 1% to 2% of capacity, it's fully charged: switch to float, nominally 13.6V.

A really smart charger will allow control of the bulk charge current, and monitor temp to back off if the batteries warm up.

Most of the smart chargers out there are very conservative, since they don't allow current programming.

One experiment I performed was, with a fairly flat (dead) house bank, increase RPM until current stops increasing - you may be surprised.

Maybe the ARS-5 is not a three-stage charger? I don't know.

 

[Maine Sail]

I thought..

My Balmar regulator was very conservative that's why I was trying to trouble shoot it with the folks at Balmar and I never would have known had I not been watching it perform on my Link 10. My charging speed at the pulley of the alt was correct at my cruising RPM to reach max output of the alt according to Balmar.

My guess is that maybe they do design them with the thought that many will not buy the temps sensors?? I agree 100% that they should do better in the bulk phase. Perhaps there is a way to make them do this that Balmar won't disclose???

The difference in charging rates/speeds between my three stage ARS-5 and my 90 amp alt with the stock regulator was very minimal and that is what I found to be extremely frustrating given the money I had spent on the "smart" regulator system. I do think they are a good investment if you need the capacity!

 

[Stu Jackson]

Guys, we had this discussion last week, at

great length, and I advised that, based on the readings from my Link 2000, even new regulators do this, but if we ARE working on the 50% to 85% charge period, with a reasonable size house bank, the acceptance rate of the battery technology will out pace the alternator's output all the time.

I see it, I believe it and as far as alternators and regulators go, I don't believe it makes a difference, because, for one thing, even your shorepower charger is MOST LIKELY a quarter of your alternator, so you're doin' OK on the amount of time it takes to charge.

The regulators, it seems to me regardless of how they are marketed, don't have all the smarts of shorepower charger, but at least do bulk up the bulk stage and make it last longer than a tapering charger (no pun interned, yeah, right)

And even if you have, like I do, a 75A shorepower charger (part of my Freedom 15 IC), the patterns of input compared to my 100A alternator is literally identical. Identical.

So, help me understand any other conclusions I can draw from that. Thanks, Stu

 

[John]

I speak English and Spanish,

but this is all Greek to me!

Hopefully, some day I'll be able to figure out what you guys are talking about.