House Battery Monitoring

Dora~Jean · Posted: Sat Oct 07, 2006 11:35 am Post subject:

John,

I regularly have kids (big now) on board. We occasionally watch a DVD movie, and they sometimes are allowed to play video games for a few hours. Other than that, we have lights at night, stereo, GPS/tide monitoring sometimes, VHF chatter sometimes, Wallas heater (miniscule current) -- and that's about it for the most part. No refer, I have an extra insulated ice chest that lasts ~5 days which is adequate for 95% of my trips. I only have 2, 110 amp-hr batteries (KISS and weight), they do fine for my lifestyle.

I never run my batteries below about 70% of their capacity (1 at a time), 50% is the recommended maximum to discharge before damage. 70% x 110 amp-hrs is 77 amp hrs. Therefore I can use 33 amp-hrs before recharging or switching batteries. For my energy needs, that's sufficient for several days. And usually we go somewhere in the boat, so it recharges after a few days anyway. If not, I throw a 30 watt solar panel on the roof and it brings back 20 or more amp-hrs on a sunny day.

Voltage monitoring is approximate at best for determining capacity remaining. While draining the battery, the voltage will give a falsely lower reading, mine is regularly at 11.8V or even lower during 4-6amp drains (DVD, TV). Temperature also affects the reading. After a 2 or more hour rest with no draining, you CAN get a feel for the % capacity remaining of the battery, especially as you gain experience with the readings. But being an approximation, you might have quite a bit of useful energy remaining while you're panicking over the reading, or conversely, you might be very close if not beyond what you should have used in order to have enough to turn over your engine on a cold morning.

I'm an electrical kind of guy and I have great peace of mind knowing exactly what's happening with my batteries and my emergency ability to use the VHF radio or start the engines. And sometimes I'm surprised to find an unexpected current drain when I check the amperage before leaving the boat or going to bed -- something left ON (usually the VHF). For me, it was one of the first accessories to be installed on my boat!

John S · Posted: Sat Oct 07, 2006 12:12 pm Post subject:

Steve, Some very interesting thoughts. I am surprised how much use you are able to get out of two smaller batteries on one charge. I haven't sat down to run all the numbers on all the different accessories we like to use while sitting at anchor, I probably should. So far it has all been a guessing game. It sounds like you went at battery monitoring the same way I went at a fuel flow meter. The navman 3100 was my first installation, for the same reason as your Link 10, piece of mind. Some good points, thanks. Which solar panel are you using? where did it come from? do you get any charge on a cloudy day? not much sun in coastal AK.

Thanks,
John

Dora~Jean · Posted: Sat Oct 07, 2006 12:52 pm Post subject:

John,

Yes, I'm able to squeeze quite a bit of usage out of my batteries. I usually only use one battery for house power on a trip, next trip I use the other. That way I always have a fresh battery to start at least one engine. I had a dead battery one time at launching, wouldn't start the engine (long story why it was dead). I started the other engine on its battery, then after a short warmup, switched to BOTH, waited 5 minutes, then started the other engine. I have Yamahas with 20 amp output, other engines may not be recommended for that trick so check your manual first before trying. It's fascinating to learn just how much or how little each accessory uses as you turn them on/off one at a time. Stereo, GPS, Wallas heater (after turn-on sequence), VHF (idle) are all surprisingly low -- less than a light bulb! The windlass under a strain uses 25-35 amps, but I supplement that with one engine revved to 1500 rpm or so while bringing up the anchor.

I forgot the name of my flexible solar panel, bought it at West Marine about 15 yrs ago, haven't seen that brand there lately. Not as efficient (size vs output) as rigid panels, but it sure is easy to store under my front bunk and deploy on my roof when needed (plugs into dash 12V receptacle). It's about 1/4" thick, maybe 18"wide by 5' long. I always smile when I see a PLUS amperage number on the meter while I'm running the stereo maybe while eating breakfast -- running on the sun and recharging my battery to boot!

Next accessory: Fuel flow meters!!! Probably Navman, still in research mode...

thataway · Posted: Sat Oct 07, 2006 2:14 pm Post subject:

John,
I did not say that my neighbor had put in a shunt or buss bar, but that he felt that there was room,if you took out the battery--on the side. There are many ways to put in electrical elements. I prefer to screw the buss bar and other accessories onto a pressure treated piece of wood, and then bolt or screw that piece of wood to the fiberglass. This way, you can rig the circuits on the board, and then put the board in after all rigged. If you need to change, just unbolt/screw the board and take it out into the open.

Yes, I have a single digital volt meter, with a 4 battery bank monitering circuit. I have used the Link and similar systems. But I also have over 45 years experience with 12 volt battery power management in boats. Some of this included crossing oceans under sail alone, with full navigation equiptment, Nav lights for 10 or so hours, SSB Radio daily, Weather Fax several times a day, and an auto pilot running full time. After awhile you develope reflexes and know rather closely how much power you are using. I measure the voltage on the battery banks, after most power sources are off for half an hour, and determine how much I have to charge.

In the C Dory22, I had no power management--only two group 24 batteries--one engine start and one was "house" wired directly to the Wallas. I carried a garden tractor (AGM) spare--it would start the engine in an emergency. For the Tom Cat 255--there are far more electronics and "gadgets" than on the C Dory22. There are two battery banks for the house--plus two engine start batteries--any one of these would run the boat--except for the freezer--and that will usually be run off one bank. I will just do the same as I did in the sailboats and check battery voltage in steady state--and be sure I don't go beyond the 12.2 volts discharge level, and then charge appropiately. I have a Honda EU 2000i and 44 amps of charging capacity on each of the engines. I had a Link on my last boat--and frankly, didn't use it, except as a battery volt meter.

Will the link give you more information? Absolutely yes. Is it essential--that is debatable. But if you are more comfortable with it--get one.

John S · Posted: Sun Oct 08, 2006 12:09 am Post subject:

thataway · Posted: Sun Oct 08, 2006 1:06 am Post subject:

John,
My Tom Cat 255 also came with an unusual battery configuration. I changed the wiring to some extent. You want to be able to use switches or relays to isolate the house batteries and starting battery. You are correct that one engine start is plenty to start the two engines which you own. But there is a risk that the house/engine start could run down, and the other start fail (very slight)--but I do like to isolate two starting batteries, and then have a separate house bank. You may have noted that I carried a U1 battery (Garden tractor) extra battery fully charged. One of these has plenty of power to start an outboard--probably would start two. It is better than one of the "jump start" kits, and cheaper.

Good luck with your decision--no matter what, you will do well.

JamesTXSD · Posted: Sun Oct 08, 2006 9:18 am Post subject:

Regarding the battery/motor start situation. Our #1 is a starting battery, #2 is two house batteries. We have brought the jumper-battery along on previous boats (didn't need it, but used it for charging cell phones, anchor light on our little sailboat with an electrical system, etc.). We figured the Honda generator would be our "back up" on the C-Dory. If we somehow managed to run down all the batteries, we'd fire up the generator to run the battery charger.

Best wishes,
Jim B.

Sea Wolf · Posted: Sun Oct 08, 2006 12:00 pm Post subject:

Beware!

Battery Back-up Overkill can boarder on an obscessive-compulsive disorder!

And excessive worry won't lower your blood pressure or count as therapy time!

I went overboard on this one when I added the engine mounted electric trolling motor:

Batteries 3 and 4 added under the forward dinette seat. (Two more Group 27's)

Honda 1000i generator on the ready/standby.

Emergency battery start pack under floor of helm station.

I've used the 1000i to recharge when trolling for over 4 hours continuously, but never the emergency start pack, and have never run the 4 27's down enough that they wouldn't start the Yamaha 90.

Still, I know I won't be paddling my C-Dory anytime soon!

Joe.

flapbreaker · Posted: Sat Jan 27, 2007 10:48 am Post subject:

I stumbled across this battery monitor. Thought it might make a nice, cheaper alternative to the link systems. "Only" $60. I have not ordered one yet but am thinking about it. Thougth I'd wait and get some opinions first.

http://www.rc-electronics-usa.com/ammeters/rv-battery-monitor.html

Dora~Jean · Posted: Sat Jan 27, 2007 1:18 pm Post subject:

Pretty neat monitor there. It also appears to integrate over time (kWh) so you'd be able to quickly calculate capacity changes. However, (the infamous 'but'), it has to be located in-line with your current draw/charge to the battery. There-in lies the problem on a boat. It would have to be mounted somewhere back by the battery(s) [unless you ran some helacious wires to carry the current all the way to the dash...!]. Also, with that light wiring, I doubt it would carry the amps to put in line with your engine's charge/starting line -- or at least I wouldn't want to try it for fear of damage to either your engine or a fire in this unit. Did it say how much current it can safely handle?

You could just put it in line with your cabin power at a feed point back of the dash, then you'd be able to monitor the current drain at least. Then just don't worry about the recharge cycle or times. You'd get 80% or more of what you need to know for most of your boat usage (IMHO).

Looks more practical for like an electric car where the battery(s) are located closer to the dash and all. Still, neat monitor for sure.

flapbreaker · Posted: Sat Jan 27, 2007 7:38 pm Post subject:

Dora~Jean,

Your probably right about it not working so well as an amp meter but I thought it would work just fine as a volt meter. Of course it would probably be something that I would just have wired to the battery so I'd have to look in the lazarette but that's better than my current system of trying to hook up my handheld multimeter.

flagold · Posted: Sat Jan 27, 2007 10:15 pm Post subject:

thataway · Posted: Sat Jan 27, 2007 10:29 pm Post subject:

Looking at the specs, it appears to have a shunt (negitive), which carries the current, built into the meter. I agree that you cannot easily mount it remotely--ie on a console, because it has to be inline with the negitive wire or the circuit. Looking at the dimensions, it is much smaller than the "normal" shunt used in one of the link systems. It looks like a great gadget--but I wonder how practical it would be considering where it will need to be mounted (access to read, weather protection etc).

Bob Austin

Casey · Posted: Sun Jan 28, 2007 12:33 pm Post subject:

We use a Link 20 on Naknek, and are very happy with it.

On one trip, Chris (Rana Verde) shared his technique. Run on two batteries, and when you stop for the night switch to one battery; even if you drain the single battery lower than intended, you still have a fully charged battery to get you going the next morning.

Even with that in mind we have never come close to running a (single) battery lower than recommended 50%. Run your Wallas, XM radio, VHF radio, etc, low wattage anchor light, low wattage reading lights with wild abandon and still have plenty of power the next morning.

The thing I like about the Link 20 (or Link 10) is that it allows you to know the state-of-battery charge ... no guessing.

Buy one - you'll like it if you're doing overnights away from a marina with power.

Casey
C-Dory Naknek

flapbreaker · Posted: Sun Jan 28, 2007 1:13 pm Post subject:

Casey, How many amp hours are your batteries. It sounds like you have better luck than me with keeping plenty of power to the house battery.