Battery condition meter!

[Louie56]

I would like to build a good acurate battery level condition meter for my boat. I have heard a bit about "percent of charge" meters and am looking for any information as to the circuitry. Any help toward finding a schematic would be greatfully appreciated..

 

[buzzp]

I believe they measure the battery voltage of lead acid batteries to determine condition. I have a link at work I will post if no one else does. Good luck

 

[cbarn24050]

Hi, try your local auto shop

 

[Louie56]

That link would be great! I know I can run down to a retail outlet and buy what I am looking for but I am after the adventure of learning the circuit and fine tuning it to my likings rather than an off the shelf purchase.
Thanks again.
Louie..

 

[Lewish]

One way to do battery testing is to AC couple, either by capacitor or transformer a 1 KHz signal to the terminals of the battery, while the battery is disconnected from the boat. By profiling the impedance of the battery, you can determine the degree of charge and predict when the battery will fail, assuming adequate maintenance of the battery. Impedance will increase with age and deteriation of the battery. It will also increase as the battery is discharged under normal use.

I hope this idea is useful.

 

[nbucska]

Connect every 5 min. a 12 Ohm parallel for a ms and sample/hold and calculate the Ri.
<nbucska@pcperipherals.com>

 

[BrianG]

You say in later e-mails you want a challenge but don't say what kind of skills you have, but you could try and build what they use for large propulsion batteries.
You need a small series shunt (or pick up across the ammeter terminals if the boat has one) to measure current: This will be one polarity when charging and the opposite polarity when discharging.

You need to build a digital up/down counter circuit and display showing say, three decades. There are many suitable logic families you can use for this. Then you need to build two voltage to frequency converter circuits. (There are single-chip solutions for these and most text books show how to do this) One V-F circuit responds to the small voltage developed across the ammeter during battery charging and makes the counter count &quot;up&quot;. The other V-F circuit responds to discharge current and makes the counter count down.

By scaling the V-F converter counting rates correctly your display shows true ampere-hours, which is how battery capacity is measured. (If you get that working successfully you can then get even more cute by adding circuits to compensate for temperature changes, different charging rates, etc.)

 

[Louie56]

My skills along these lines are limited, more along the hobbiest line. I can manage to follow a schematic and wind up with a working model but my knowlege lacks when it comes to circuit development.
The application I will be useing this circuit on is needed for discharge and current condition only. Any chargeing is done on shore via a 110v battery charger. Basicaly, I want a much more accurate measureing method than is supplied with electric trolling motors. You get four led's and by the time these thing s start giving an indication its already gone.
Thanks for your help.

 

[sailingzeus]

There are Amp. hour meters ranging from $150 to $500 for multiple banks. However I understand your desire to do it your self, I was looking to do the same last month. BrianG seems to know what he is doing, I need to translate into layman's terms. Good luck.

 

[jbartos]

Suggestion: I have been testing lead-acid battery cell used to power an electric truck in a manufacturing facility.
The meter was very simple and the test too. Simply, a small voltmeter was attached to a high power resistor (about cigarette pack size). The meter had two sharp knives that were used to make short for a second or so across the battery cell. The meter reading (voltage) indicated the battery cell quality and charge. The higher the meter needle deflection, the better battery cell quality. The meter was calibrated in the battery cell charge quality, i.e. percentage. To design this meter, you will need to have a voltmeter (fairly rugged housing) and the resistor (size will have to be calculated and some experimentation needed). Then, there is a need for two copper knives that could possibly be obtained from copper bars. Some wood or plastic handle would be also needed. Once it is done, it will resemble a fork with a meter and resistor that get very hot so that it may be a good idea to cover it by some guard.