battery condition

[tgalea]

I have recently posted some questions in this forum regarding the installation of a voltmeter and ammeter on my boat and got a variety of replies for which i thank-you all.

So basically to put it this way what i am after is being able to verify my battery condition and checking that it is being charged. I imagine that by reading volts and amps i should be able to do this however most of the replies mentioned the fact that these two instruments will not jointly really give me a good picture of the situation.

Any suggestions to what i may do ? I am not too happy at the moment with no method to verify my battery. I don't know if it is being charged properly, etc.

Your help would be much appreciated.


Regards

Tyrone.

 

[Chris_Stannard]

Hi,

Its me again, the answer to your problem is two fold.
Firstly if you have a Voltmeter (Digimeter) in your tool kit you can check the batteries at their terminals. you should do this about 30 minutes after charging has stopped. If, as is likely you have two batteries in parallel, you should disconnect one before taking the reading. The batteries, if fully charged, should be over 13 volts the more the better.
Second test, and advised if you have lead acid batteries, buy a hydrometer from Halfords of the chandlers. Should be less tha a fiver. Take a reading from all of the cells in turn again having given the battery a rest after charging. You do this by sucking some of the battery fluid up into the device and seeing where the float settles. It should have a green sector, which means there is a good charge, a white meaning okay but could do with a charge, and a red meaning the batttery needs charging now. BE CAREFUL with the fluid, it tends to drip and if it gets on your trousers it will burn holes in them, being weak sulphuric acid. (I speak from personal experience and SWMBO was not pleased).

The readings from all of the cells should be close to the same, 1320 or above if the battery is charged. If you have a cell where the float just sinls to the bottom, the battery is caput and needs replacing, since you have a collapsed cell.

Just to cheer you up my Navtex went U/S last weekend and I have a problem with my fresh water system, not looking for sympathy but it might make you feel better.

Chris Stannard

 

[VMALLOWS]

The trouble is the distiction between an 'automatic' charging system , and actually understanding, and responding to, what your battery really needs.

Given a voltmeter (a decent digital one) and an ampmeter (anything that shows the charge to within a few amps) , and a memory of what went in/came out I can manage my batteries .

My problem is that I always end up having to motor home in a good breeze just to charge the batteries!

Anyone got a windwane going cheap?

Seriously, the main thing is to watch the battery voltage. You must wait at least 30 minutes after charging or discharge so the best thing is to check them when you come onboard. A new battery will show about 12.7v (or even 12.9v) fully charged. An older one is more probably 12.5-12.6. A dud one is 12.2 and not responding to charge.

 

[halcyon]

Voltmeter and ammeter can give you a could idea of battery state, assuming that the ammeter is in the main service battery feed.
Charging, if you alternater regulates at say 14.4 volt, once amps drop to 2/4 amps and voltmeter reads 14.4 your not going to put much more in, gives you around a nominal 80% battery recharge capacity.
In use ie with engine of, and using power, as a nominal guide (based on a average load of 5% battery capacity ) 11volt flat, 11.5 volt 25%, 11.85 volt 50%, 12.2 volt 75%. If you keep the voltage above 11.85 volt in use, 12.4 volt no load, charging them at this level you should have little problem.
You can leave out the ammeter if you want, just charge upto the regulation voltage of the alternater, and after 30 min your not going to put much more in.
The main reqiurement is that the battery is recharged to 14.4/14.6 volt, if say you have blocking diodes and drop 0,6 volt, 14.4 becomes 13.8 volt and 60% battery capacity. This will also give you a low bottom end voltage in use leading to bad battery live due to sulphation etc.
For more cost you can go for capacity gauges ( a cross over from the fork truck / golf cart industry ) measures amps in amps out. One point is that you lose amps in due to battery efficiency, and you lose amps out due to battery efficiency, so actual value need not be the same, a bit like gps.
You can add a smart alternator regulater for more money, if you have blocking diodes or a low regulating alternator, a better buy. But if you are getting 14.4/14.6 volt to the battery, you will not gain a massive amount. Up to the regulation voltage you have no gain, it is the area above the 14.4 /14.6 volt that you gain capacity.

At the end of the day it depends on the depth of your pocket.

All the best

Brian

 

[kgi]

know the problem, i would fit the boat with an external regulator on the alternator and set it for 14.2 voltsthat way you dont gas the batteries and boil them dry,what i did on my own boat was fit solar panels also with an external regulator and that keeps my batteries right up,stops sulphation as well so the batteries last longer, remember if you fit a solar panel, that the larger ones like the siemens sp75 will toast your battery in no time. ps if you can get hold of a westmarine catalogue from somewhere (cruising boat) they are full of useful information

 

[Plum]

The most useful instrument is a digital voltmeter. Must have minimum resolution of 0.1v and an accuracy of 0.2%.

While charging the voltage should be somewhere around 13.8 and 14.2, but once you get used to your normal charging voltage, any change will tell you something is not right.

With the engine off and no charging for at least 30 minutes the voltage will tell you the condition of the battery (assuming reasonable ambient temperatures). A good guide to voltage was posted on this forum some time ago (can't remember who) and is easy to remember as it rymes: 12.7 they're in heaven, 12.5 they're still alive, 12.2 charging due, 11.8 is much too late.

A suggested voltmeter is available from www.rswww.com stock number: 365-6252 cost: 20 pounds

 

[tgalea]

Thanks for your time again chris.

Yes so i will take up your suggestion. Unfortunately i just bought myself a new sealed battery so can't check it with a hydrometer but the digital meter should be the solution.

The thing is that as i said i am so disappointed that i have to rely on shear luck that my battery is being charged. i just bought this boat a few months ago and she has no battery monitoring / charging info at all! The other day i went to start and didn't manage.. then found out my battery was too old and needed replacing but still i believe in prevention rather than cure.. i wanna know if i have a good battery ready to start me up or not!!!

Cheers mate.

Tyrone.

 

[JerryHawkins]

Get a Link10

Bite the bullet and buy a Link10 battery monitor (or similar - several around). This acts just like a fule gauge for your battery. I bought one a month or so ago, when I replaced my batteries. It tells you the state of charge and, more importantly, at the present rate of discharge how long you have left before its empty! You can set the discharge threshold so that it will tell you the battery if flat when in reality its (say) still 50% charged.

Expensive at around £200, but IMHO worth it if you rely to any degree on your battery.

Cheers, Jerry

 

[jollyjacktar]

Blocking diodes in parallel

If you place blocking diodes in parallel with the main battery selector switch then you can charge batteries but not discharge them with the switch in the off position [saves burning out alternator if with say with a diesel, the main switch is accidentally switched to the off position with the motor running] .

This will have an added advantage of automatically charging the lowest battery quicker in the "both off" positions, or giving preference to the battery selected in the selected "on" position, since with the switch in parallel with the diodes, selection of "on" positions thus will be the least resistance and current will flow thru the switch not the diode and gain advantage of full charge without the diode voltage drop to the battery selected. However charging with the switch in the "both on" position will not give surge protection.

Further it will not effect power usage selection with the motor off and not charging.

I think this all makes sense... draw a circuit diagram and figure it out for yourself. Unfortunately without the picture I have to use a thousand words.