by dave-r » 22 Mar 2001 12:34 BATTERIES
The battery in your car serves four basic functions;
1) It supplies power to start the engine.
2) It supplies power to accessories when the engine is not running.
3) It supplies additional power to the electrical system when demand exceeds alternator output i.e. at idle when several accessories are switched on.
4) The battery also acts as a buffer in the electrical system, smoothing out voltage surges and spikes, and stabilizing the system charging voltage.
Buying A Battery
When you are looking for a new battery it is helpful to compare specifications. These relate to test procedures that have been used to rate a battery's performance and durability.
The three main specifications you may come across are;
1) COLD CRANKING AMPS ( C.C.A.) : This is the battery's ability to deliver high current (AMPS) under extremely cold conditions. This is very useful in cold climates but in hot weather a high C.C.A. rating can be detrimental to a batteries life.
2) RESERVE CAPACITY ( R.C. ) : This is the measurement of the battery's ability to supply power without the aid of the vehicles charging system. For example if you lost your fan belt you would have to rely on the batteries R.C. to get you home. The test is done by measuring the amount of time that the battery can deliver 25 amps and still maintain at least 10.5 volts at the terminals. This time, in minutes, is the R.C. rating. When selecting batteries this is the best measurement to use.
4) DEEP CYCLING : This is the battery's ability to withstand repeated complete discharge/recharge cycles and still perform to specified standards. Don't use deep cycle marine or R.V. batteries in your car as they are not as good at starting a cold engine on a cold morning.
In general, when replacing a battery that has provided a good service and long life, replace with a battery of equal C.C.A. and equal or greater R.C.
Battery Types
There are three main types of automotive battery;
1) LEAD - ACID : This was the original auto. battery. Their good points are that they produce a high C.C.A. rating and can be deep cycled several times while still delivering a good service.
On the bad side they use a lot of water, which needs frequent topping up, they gas heavily when charged and display a high level of terminal corrosion. This leads to a tendency to self discharge and a short shelf life.They also have a relatively short life span under normal use and are adversely affected by high temperatures.
2) LOW - MAINTENANCE : As suggested by the name, these have similar characteristics to the lead - acid types.However they use much less water and gas less when charging. They still have removable filler caps so that the cells can be topped up with water, if necessary, but this is seldom needed. They also have a better shelf life although they still need to be monitored if sitting idle for a long time.
3) MAINTENANCE - FREE : These do not need any water added during normal operation. However if these batteries are subjected to severe operation, such as extended overcharging or several deep cycles, they can use water just as with the other types. Unfortunately there is no provision for adding water if this is the case. Also after being deeply discharged they may never fully regain their complete charge. When recharging, a higher voltage is needed because the cells used are more resistant to accepting a charge so cars that came with these batteries as standard have charging systems with a higher output.
Battery Performance
The main things that effect battery performance are the weather (temperature), low acid level and corrosion. Cold temperatures slow down the chemical process within the battery. At zero degrees F. a fully charged battery delivers only 40% of its capacity. On top of that, in low temperatures, it takes twice as much cranking power to turn the engine over and start the car.
Another thing to look out for is to not allow the acid level to drop to a point where the top of the cells are exposed to air as this will oxidise the plates. It is also very important to only top up with distiled water. Tap water will cause sediment to build up in the bottom of the battery which can eventually short out two or more cells and ruin it.
Something which we have all been guilty of at one time or another is to allow corrosion to build up on the battery terminals and cable ends. This results in poor conductivity of electricity. So they must be periodically cleaned and coated with high temp grease.
If you do not use your car for long periods then it is important to keep the battery in a fully charged condition.
Your battery should be clamped down securely as shock and vibration can shorten its life.
If you re-locate your battery to the boot (trunk) it is even more important to ensure that all connections from the battery to the car are good and that there is sufficient ventilation to prevent a build up of fumes. When I did this to my Challenger I bought the heaviest cable I could find that would fit the cable terminals and I have never had any trouble turning the engine over to start it.
By MoparKev (Kev) on Thursday, March 01, 2001 - 09:59 am:
Hi Tech Dude!
Howsabout the new generation of solid state battery such as the Optima range and the Hawker SBS red tops? These seem to be the best battery ever! Do you have your starter relay in the trunk, for safety reasons?
By David Robson (Dave) on Thursday, March 01, 2001 - 10:15 am:
Kev.
I'm an old bloke and only know about/have reference to old stuff. If you have any info on these please write it up here.
I have a heavy cable running directly from the battery to the starter motor. This is the best way to do it. Everything else is tapped off from there by a cable running from the same terminal on the starter to the live post on the inner fender where the battery used to connect to.
By MoparKev (Kev) on Thursday, March 01, 2001 - 10:48 am:
That's how I have mine, but for safety a remote starter relay should be used and a separate fused line to the distribution block on the inner fender. At the moment we both have a 20mm live unprotected (IE No means of breaking a fault current) battery cable running the whole length of the car. In the event of a crash or chaffing of the cable the resulting fire will no doubt destroy our cherished Mopars. Food for thought!
By David Robson (Dave) on Thursday, March 01, 2001 - 10:58 am:
I did wonder what to do about that. I have put a heavy plastic wrapping around the cable in places where it passes anything like a sharp edge.
Have you a circuit diagram for the system you describe?
I take it that during normal running you have a fused heavy wire running everything but during cranking the relay shorts out the fuse or directs the current down another cable that is un-fused?
Is that right?
By MoparKev (Kev) on Thursday, March 01, 2001 - 11:11 am:
You have the heavy cranking cable in place already. You need a remote starter solenoid that is mounted in the trunk. The solenoid on the starter needs to be shorted out and the control wire from the ignition run back to the remote solenoid in the boot. In effect you have moved the starter solenoid back down the line. The fused wire to the control circuits on the inner wing is totally separate but should be of sufficient size to take the volt drop into consideration. This way you only have the large cable live when starting the car, whilst running the smaller fused cable does all the work. Hey presto a safe car!
By David Robson (Dave) on Thursday, March 01, 2001 - 11:38 am:
Yep I get it now Kev. You would not need two cables though. I think you would just need one heavy cable and then you make the relay short out the fused bit while cranking.
By David Robson (Dave) on Thursday, March 01, 2001 - 01:39 pm:
CHECKING THE CHARGE IN YOUR BATTERY
There are two ways of doing this. The most accurate is to check the specific gravity of the acid with a hydrometer. The other method is to measure the voltage on the battery with a voltmeter.
Pure water has a specific gravity of 1.00. Pure sulphuric acid has a specific gravity of 1.84 which means that it is 1.84 times heavier than water. When these are blended in a fully charged battery the mixture has a specific gravity of 1.270. This mixture is called the electrolyte. As a battery is discharged the amount of acid in the electrolyte goes down and the amount of water goes up. This results in a drop in the specific gravity of the electrolyte which can be measured with a hydrometer.
Hydrometers can be purchased from tool shops and work by drawing up the electrolyte with a rubber bulb into a glass tube. The measurement is taken from a float in the tube.
<TABLE BORDER=1><TR><TD>STATE OF CHARGE</TD><TD>SPECIFIC GRAVITY </TD></TR><TR><TD>100%</TD><TD>1.270 </TD></TR><TR><TD>75%</TD><TD>1.225 </TD></TR><TR><TD>50%</TD><TD>1.190 </TD></TR><TR><TD>25%</TD><TD>1.155 </TD></TR><TR><TD>0%</TD><TD>1.120</TD></TR></TABLE>
Of course with maintenance free batteries it is not possible to draw off any electrolyte. The only way to check these batteries is to measure the voltage at the terminals.
To do this you must use an accurate voltmeter (digital is best).
First, if the battery has been charged within the previous 24 hrs, the surface charge must be removed before a measurement is taken. This can be easily done by turning on the headlights for 2 or 3 minutes or disabling the ignition spark and cranking the starter for 10 to 15 seconds. The voltmeter can then be connected to the battery terminals and the exact voltage measured.
<TABLE BORDER=1><TR><TD>STATE OF CHARGE</TD><TD>VOLTAGE </TD></TR><TR><TD>100%</TD><TD>12.60 </TD></TR><TR><TD>75%</TD><TD>12.40 </TD></TR><TR><TD>50%</TD><TD>12.20 </TD></TR><TR><TD>25%</TD><TD>12.00 </TD></TR><TR><TD>0%</TD><TD>11.80</TD></TR></TABLE>
While charging a battery, on a battery charger, monitor the charging rate on its meter. When the rate has stabilised at a low rate for a hour or more the battery is fully charged. The best type of charger is one that maintains a constant charging voltage but limits charging current (AMPS) as the battery reaches full charge.