Battery monitor

Maine Sail · Jan 11, 2012

Tanqueray said:
I have a Hunter 280, with 2 batteries and a Guest battery charger. At the end of the season, the Guest indicated that one of the batteries was not charging correctly. After haul-out, I took each battery to my local auto parts store and asked them to test them...they both tested "OK".

Would one of these battery monitors be of value to see how charged the battery is during extended trips (meaning a couple of days away from the marina)?

I am also considering one of those "power pack" jump starters in case I run down the house batteries and cannot start the diesel.

Any thoughts?

Greg

Greg,

An analog volt meter won't tell you much while actively cruising. That will tell you if the batteries are actually charging but not a heck of a lot more, at that scale. A cheap DVM will tell you more closely to accurate what the voltage is at the moment but that in and of itself does not tell you much about state of charge unless the batteries have been allowed to reach a "resting voltage"...

What are you looking to get out of it accuracy wise? Is it a situation of "is my alternator on & working", or "my battery is at 56% state of charge" that you're looking for?

Stu Jackson · Jan 11, 2012

Tanqueray said:
But I don't know too much about batteries.

Greg, one choice is to learn about them. A good place to start is www.amplepower.com, and download the Ample Power Primer form the tech tab.

You could also read the Electrical section here: http://www.westmarine.com/webapp/wc...51&catalogId=10001&page=West-Advisor-Articles

Bill Roosa · Jan 12, 2012

While I will concur with MS that a volt meter will not tell you much I would add "if you don't have a tool to help"
http://www.scubaengineer.com/documents/lead_acid_battery_charging_graphs.pdf

If you beleive the author, resting voltage is even more misleading than voltage while discharging. I've used this technique since I started boating and have only had one case where I could not get the engine started. That was related to the failure of the isolation diode.

Benny17441 · Jan 12, 2012

I would suggest that if you do not already have a battery switch that will allow you to combine or separate the two batteries that you invest in one. You can use one battery and leave the 2nd one as a backup. By alternating their use whith each outing they will both get similar usage and should render a similar useful life. Getting a battery pack and keeping it charged and aboard will allow you to push your battery limits even further. Don't know if in your location it is offered but having unlimited towing and emergency insurance can be a blessing if your batteries are dead as they will come and provide you a jump to get the engine started. Besides that you get towing, emergency fuel delivery, they can help locate parts in unfamiliar places and may even have divers available to unwrap a line from a prop. I would think these recommendations would ease your concerns about being unable to start the diesel. I know most of the engines today cannot be handcrancked. Boats with sophisticated electronics and expensive battery banks do benefit from the use of a battery monitor but in the usual applications they are unwarranted because of the cost.

Benny17441 · Jan 12, 2012

These auxilliary diesels are small and have efficient starters so a deep cycle battery can adequately be used for engine starting. Having two deep cycle batteries can give you more options to use for house. The article is very good and I specially liked the comparison that using a voltmeter is like tracking a bear. With experience, observation and practice you may develop a sense of the state of you battery bank by just looking at the voltmeter. The voltmeter is not as useless as some claim.

Maine Sail · Jan 13, 2012

Tanqueray said:
I have a battery swith, and was taught to alternate batteries as you suggest during my sailing classes. However, if one is a deep cycle and 1 is a starter battery, I am assuming that I should use the starting battery to start the auxillary, and use the deep cyle as a "house battery" while underway.

My needs are pretty simple, and I would just like to get some undertanding of the SOC of my batteries to better understand if they are in decent condition, how disharged they get under normal use. The "back-up" would be necessary only if something bad happened to both batteries and I could not start the diesel.

I am still reading some of the information suggested by Stu (trying to digest it is more accurate), and the AmplePower site discourages the use of a 1-2-both-off battery switch.

I will read the article you offered...as I said, my needs are simple and I am not going to invest a lot of $$ for a digital amp-hour meter.

Thanks,

Greg

PLEASE ignore that rubbish. Ample sells battery switches and their claims are no where near the reality. There are literally millions of these in use, safely....

Mike Culik · Jan 13, 2012

Greetings all,
Check out the Voltage meter from sailorssolution.

http://www.sailorssolutions.com/index.asp?page=ProductDetails&Item=VM01

Santa just bought one as a stocking stuffer and I installed it last week. Much much better than my old meter.

Agree with Benny, knowing the age of your battery and how the charged state is maintained should give you some confidence in your battery bank. I’m a little anal in that I log my battery voltage daily and load test my batteries every spring.

Jackdaw · Jan 13, 2012

Maine Sail said:
PLEASE ignore that rubbish. Ample sells battery switches and their claims are no where near the reality. There are literally millions of these in use, safely....

For sure that is an overreaction, perhaps with an agenda. It's like telling people not to bathe because last year 3 people drowned in their tubs.

I don't like standard switches only because of the risk of operator error, either them being turned off while the engine is running, or forgetting to uncombine after it has.

For that reason I use blue sea systems ACR and battery switches.

http://bluesea.com/category/78/1/productline/overview/329

Jackdaw · Jan 13, 2012

Stu Jackson said:
Greg, one choice is to learn about them. A good place to start is www.amplepower.com, and download the Ample Power Primer form the tech tab.

I was looking at the wiring diagram on the ample site, and noticed that they wire the house bank directly to positive distribution without a switch. Is this wise? As I look at there is no way to isolate the house bank in the event of an internal short.

http://www.amplepower.com/primer/nextsys/index.html

Maine Sail · Jan 13, 2012

Benny17441 said:
These auxilliary diesels are small and have efficient starters so a deep cycle battery can adequately be used for engine starting. Having two deep cycle batteries can give you more options to use for house. The article is very good and I specially liked the comparison that using a voltmeter is like tracking a bear. With experience, observation and practice you may develop a sense of the state of you battery bank by just looking at the voltmeter. The voltmeter is not as useless as some claim.

A volt meter can be useful but when a 10% difference in charge level is approx 0.11V the scale and accuracy become very important. The difference between 100% SOC and 50% SOC using open circuit voltage as a measurement is around 0.62V... That is all the OCV change you see between 100% SOC and 50% SOC..

When that 100% to 50% SOC difference is just 0.62V then the quality and accuracy of the meter, and the scale you're looking at, become quite important. The scale and accuracy of the volt meter becomes pretty important if you want to know anything less than a 30-40% variation in approx battery state of charge using an analog meter on a boat. The boat I am working on currently reads 14.9V when charging at 14.4V. That inaccuracy represents the entire state of charge range between 50% and 100% state of charge.

At this scale it will tell you the alt is working and not a heck of a lot more. On a good day, after it has been calibrated, you may get within 20-25%. I certainly have never been able to determine a 0.11V difference with a scale like that when the range between 12 & 13 volts is 5 marks.

If one could tell the difference between 100% and 50% SOC with this meter you're doing pretty well. I certainly can't tell a 0.11V/10% difference.. Maybe if you calibrated it against an expensive Fluke it would give you an approximate but I rarely find these to be accurate to within a half a volt.....

dfast7181 · Jan 13, 2012

Just to add my two cents worth, I went to the boat this last weekend and when I turned the key the starter acted like the batteries were dead. (4 group 31 AGM's that are six months old and new charger) I checked the battery charger and it said the batteries were full and were on trickle charge. The Link 20 battery monitor also said that the batteries were full. The volt meter said the batteries were full but they would not turn over the starter. I had the electrican come out and look and he told me the batteries look good and was suprised when the engine would not turn over. Took the batteries to be checked and was told that they had plenty of voltage but no amps. So I'm not sure that the battery monitors will tell you what you want to know, namely is there enough power to start the engine.

navigator97 · Jan 13, 2012

Check out the Volt Minder UPG 71730
http://www.batterystuff.com/images/products/717_volt_minder_md.jpg
I bought and installed 2 of them - one each for Batt 1 and Batt 2 with a SPDT switch so I can turn them both on when I want and not leave them on. I have been pretty satisfied with them. I log the Volt Reading of each battery when I come aboard for the day. Thatway I can see it anything strange has been going on regarding discharge. Not as good as a good voltage monitor system, but it will do.

Steve Dion · Jan 13, 2012

Greg:

I assume that you have a Yanmar 2GM. If you EVER have a starting issue be sure to OPEN the compression levers to get the engine spinning. Then you can close them one-at-a-time. We have done this before and you would be amazed how little energy it takes to spring the starter with any compression in the cylinders.

If you have a matching pair of batteries on your boat you may want to consider putting the two existing batteries in a single bank and getting an additional battery for the starter bank. That way you will have adequate power for house keeping and always keep you starter battery as your reserve.

These back up packs have to be topped off to do you any good in an emergency.

Battery monitor

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