Battery Monitor

Chuckbear · Jan 27, 2009

It really depends on your usage. If you are not going to be sitting at anchor running equipment a lot and since your battery set up is minimal than the expense may not justify it. If day sailing and occasional overnights are your main use that a volt meter and amp meter at the breaker panel will tell you the state of the battery at any given time.

Tim R. · Jan 27, 2009

Xantrex has a few units that work nicely. I use a Link 20 that monitors my 2 banks. I paid about $250.00 I believe this to be economical but you may not.

Mike B · Jan 27, 2009

Not sure how much gear you plan on running at anchor or how it will compare the the capabilities of a G27, but before you drop money on a monitor I would work up a power usage table. Figure what each device will draw in amps and how many hours a day you expect the device to be operating. That will give you an idea of what you'll need in battery power to support it. You may find additional battery power to be your best first investment. Once you have the power you need then drop the money on a monitor if you still feel the need.

sailaway78 · Jan 27, 2009

If it were me

I would spend the money first on improving the house bank. My feeling is that you ned to have the capacity to run the boat, before you need a monitor to check on it. One group 27 isn't going to give you much power for a weekend. Two golf cart batteries from Sams will give you 225 amp hours, for under 150 bucks. The second thing I would do is to improve the alternator output. You can replace it with a 70 or 80 amp unit for under 100 bucks. Next would be a monitor if you feel you need it. I found a 70 amp alternator at an alternotor shop for 70 bucks. This is an easy replacement on the Yanmars. I can tell you which one to look for if you want to drop me an e mail.

Maine Sail · Jan 27, 2009

Batteries

Gary,

Batteries should not regularly be discharged below about 50% of full. Doing so will drastically shorten their life span. A single group 27 as a house bank is generally considered inadequate for anything more than day sailing. The average group 27 deep cycle battery has between 95 & 110 amp hours of capacity. At a 50% discharge from full you will have only about 50 amp hours to effectively use. Of course if you are away from the dock and charging via an alternator the most you will ever likely get it charged back to will be between 80 & 90%. At a 90% re-charge you'll have only 45 amp hours of battery and at an 80% re-charge only 40 usable amp hours.

I agree with others that you should consider increasing your house bank to at least two group 27 or 29 deep cycles or two 6V golf cart batteries before adding a battery monitor.

Unfortunately checking state of charge on a boat, with a digital volt meter, while also using the boat, is tough because the batteries ideally should sit for a min of about four hours with no current being drawn off or put in to achieve an accurate resting voltage to determine state of charge.

Battery monitors are a wonderful addition given that you have already done an energy budget and sized your bank appropriately. I always recommend a battery monitor before an alternator upgrade as often times you may find out you don't need a bigger alt at all and they can save you money....

My laptop (Macbook) burns between 3.5 & 7+ amps per hour and my 19" LCD 12V TV burns 3.9+/- amps per hour. One hour of TV per day and one hour of laptop use and you've used close to, or more than, 25% of your total group 27 house bank capacity when using a 50% discharge level and alternator charging to 80% of capacity.. Now add running lights, cabin lights, GPS, VHF, Stereo etc. and your group 27 is gone in just a few short hours of use..

Chuckbear · Jan 27, 2009

Gary, I would not add a pair of Golf Cart batteries to your existing house bank. You will have all kinds of charging issues. You need for the house bank to be all matching batteries and a pair of what you have now, although better, will still be small if you plan on doing any cruising. Four, or two pairs of GC will give you about 400+ AH so that might be a good starting point. For regular cruising you will want a battery monitor. Xantrex, while being very popular is having some problems lately with their equipment so you might look at alternatives.

Bill Roosa · Jan 27, 2009

Battery monitor vs volt meter

Can someone tell me why we can't just read the battery voltage to determine the charge. I seem to recall that there is a 1:1 relationship between state of charge and voltage.
I've been doing this for some time now and it works fine.

Chuckbear · Jan 27, 2009

Bill Roosa said:
Can someone tell me why we can't just read the battery voltage to determine the charge. I seem to recall that there is a 1:1 relationship between state of charge and voltage.
I've been doing this for some time now and it works fine.

Bill, When cruising we use a lot of our battery power at anchor running various equipment so on a typical evening at anchor we will use 50 to 75 Amphours from our house bank. The next day we can run the engine or let the solar panels and wind generator put those AH back in the batteries. But looking at the volt meter while the engine is running or solar panels are charging will only give me the voltage going into the batteries and not the state of the charge. Only until the AH used has been replenished are the batteries fully charged. A voltage meter can't tell me that. Constantly undercharging batteries will kill them quickly. This might be a bit over simplistic but might answer your question.

Maine Sail · Jan 27, 2009

Bill Roosa said:
Can someone tell me why we can't just read the battery voltage to determine the charge. I seem to recall that there is a 1:1 relationship between state of charge and voltage.
I've been doing this for some time now and it works fine.

There certainly is a direct correlation between voltage and state of charge but it needs to be taken at resting voltage. You can not really accurately measure state of charge without letting the battery come to a resting voltage. This takes time. How long do you let it sit with zero draw and zero charge before taking your voltage reading??

Before measuring state of charge, the battery should have rested for 4-8 hours after a charge or discharge cycle and resided at a steady room temperature during this resting period. A cold battery would show slightly higher voltages and a hot battery would be lower. With sufficient rest and a stable temperature, voltage readings can provide a fairly accurate state of charge estimation. Unfortunately it is a very, very rare situation, while on board cruising, that you will let your batts sit for 4-8 hours with zero input or output. Taking a reading of anything other than a stabilized resting voltage really tells you very little and can be misleading..

Bad Obsession · Jan 27, 2009

I have a link 10 in my Catalina 30. It cost about $150. It was easy to put in and wire. My house bank is two group 27 batteries. I have never gotten below 90% on my batteries even when sitting on anchor for three days and running the laptop and other things. That being said, I don't have refridgeration on my boat so that makes a huge difference.

Stu Jackson · Jan 27, 2009

NEXT STEP???

reread what Maine Sail has suggested to u and the others, put it all together

== Upgrade your bank

== Decide whether you want to install a monitor

== If so, one bank or two bank monitor (I suggest a one bank is adequate for your purposes)

Go sailing! Enjoy.

walt · Jan 27, 2009

I just picked up a charge monitor (for my own set of reasons) so this may be of interest to you. This is a quick summary of all the different Xantrex models. Xantrex web site:

http://www.xantrex.com/web/id/10/type.asp

Link Lite - full monitoring of a single battery, voltage monitoring of a second battery. Consumes /uses 9 ma current to monitor ( .216 amp hours per day)

Link Pro - adds battery temperature external monitoring over the Link Lite. Also uses 9 ma of current to monitor (.216 amp hours per day)

Link 1000 - single battery full monitoring and interface to the Xantrex Feedom series inverter charger. Uses 25 ma current to monitor ( .6 amp hours per day)

Link 2000 Single battery full monitoring plus second independent monitor of a solar panel (likely also work with a second battery). Interface to Xantrex Freedom series inverter charger. Uses 28 ma of current to monitor ( .672 amp hours per day)

Link 20. Two battery full monitor. Uses 28 ma to monitor ( .672 amp hours per day).

I bought the Link Lite. I like that it uses less current to monitor ( .216 amp hours per day) and I only have one battery I want to monitor. In fact, I have only one battery period since I have a pull start outboard. I cant tell if it has any internal temperature monitoring but if I cared a lot about this, I would have got the Link Pro. All of these models only have .1 amp resolution which I dont like. For example, if you are wondering what leaving LED lights on does, the current is way below the resolution of the monitor. I think the link Lite is also the least expensive.

The link lite also has a programable alarm which can be used to either turn on or shut down an external charging source depending on battery state. Dont know about other models for this feature since Im probably not going to use it.

Dont know if I really needed the monitor but I like having it..

Chuckbear · Jan 27, 2009

Gary, I suggest some alternatives

http://www.affordable-solar.com/tri.metric.2020.battery.system.monitor.htm
http://www.batteryjunction.com/r102-bk.html
http://www.victronenergy.com/battery-monitors/bmv-600 and bmv-602/
http://homepages.ihug.co.nz/~bvdb/vah35.html
http://www.vmg-marine.com/Battery-Monitor.html

The Victron is absolutely first class and top of the line.

Maine Sail · Jan 27, 2009

Chuckbear said:
Gary, I suggest some alternatives

http://www.affordable-solar.com/tri.metric.2020.battery.system.monitor.htm
http://www.batteryjunction.com/r102-bk.html
http://www.victronenergy.com/battery-monitors/bmv-600 and bmv-602/
http://homepages.ihug.co.nz/~bvdb/vah35.html
http://www.vmg-marine.com/Battery-Monitor.html

The Victron is absolutely first class and top of the line.

Chuck,

The Victron BMV501 is the identical unit to the Xantrex XBM. I believe Victron made the XBM for Xantrex. If you can still find an XBM (Victron and Xantrex have apparently parted ways) it will likely be less money than a Victron yet the same quality.

I have had zero issues with my XBM but Xantrex is no longer listing them on their web site. There are plenty of the XBM's left in stock at chandleries though and should be a good value..

A Victron BMV501

My Xantrex XBM

Scott B · Jan 27, 2009

I'm also in the process of getting a Link monitor, see my thread further down on alternators.

The Lite and the Pro will monitor the voltage of a second battery, which, if it is a dedicated engine battery is probably sufficient info. The Pro adds battery temp input as well as historical data on your power usage.

Maine Sail, the Pro is a replacement of the XBM

Note: The LinkPRO Battery Monitor is the direct replacement of XBM Battery Monitor with expanded features.