Charging/Battery problems

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Rob_Quads
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Charging/Battery problems

Post by Rob_Quads »

Friedns got a slight problem with a Saxo VTS of his. Car is wired with an aux Deep Cycle battery used for his stereo. This battery is connected to the main battery via a large relay which is triggered by the ignition i.e. with ignition off the battery is isolated to the main battery
Not used the car in a few (5/6/7ish weeks). Went to start it and it was fairly dead (Car Battery read ~7v, Aux battery 8v!)
Using a boster pack the car was start - first time start with no problems.
Checking the voltage across the battery terminals was giving ~15/16v which to me seems very high.
Car was idling for 10 minutes then driven for around 20.
The next morning the battery was dead again and the car would not start, again booster pack was used.
What are peoples thoughts....
a) Pretty sure the main battery will need replacing as going so low will have screwed it.
b) Would the high charging voltage just be a spike while it tries to charge the totally flat batteries?
c) Do you think the alternator is gone (we regulator on it at least)?
d)
Currently we are trickle charging the main battery to see if it will hold any charge.
puc
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Post by puc »

check the charging by connecting an ammeter between the alternator and battery and running the car. reading should be between 4-8 amps. switch off, drain the battery a little by using headlamps, wipers etc for about 1 minute. check amp delicery again, it should have risen to 10a or above. also check that something isnt causing a drain. use the ammeter on the milliamp scale this time.
jeremy
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Post by jeremy »

Firstly take care with current readings on a multimeter. Many of those with a 10 amp range have no protection on that circuit and will blow if overloaded. If you suspect a leakage then start testing with a bulb in series with a battery connection and if that doesn't glow brightly - then use your meter on an appropriate scale.
Leaving a battery discharged won't do it any good but I wouldn't expect 7 volts over a few weeks to be a terminal problem. If the battery was weak - well that may all combine to finish it off.
15 - 16 volt charge form a normal alternator suggests the regulator on the alternator has failed. The effect will be to make the battery gas and need topping up as well as causing the plates to disintegrate due to excessive gassing breaking up the spongy lead. It will also overload the rest of the car circuits and will shorten bulb life and could damage some of the electronics. A corrrect reading would be about 14.6 volts.
Presumably if the relay has been installed correctly the effect is to isolate the sound system from the rest of the vehicle electrics. As both batteries have discharged more or less completely over the same period leakage in the car circuits may not be a problem. There will of course be some standby current for the alarms etc as well as clocks.
My guess - alternator failed, main battery has run dry and will need replacing too.
jeremy
Russell
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Post by Russell »

Hi,
I go with Jeremy's guess.. I think your battery problem doesn't make a lot of sense, unless both batteries are knackered, probably by the alternator.
The alternator output is way too high, this will screw up and dry outboth batteries, should be about 14V when running.
Check for drain as suggested, and the isolation relay working properly when the ignition is off, (check the drain on both batteries). Sadly, I reckon you will need some new ones, after the alternator is fixed.
cheers
Russell [:(]
Rob_Quads
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Post by Rob_Quads »

Looks like the main battery is holding charge OK now. Voltage should not have affected the deep cycle battery as its designed to withstand up to around 18v.
Just need to check on the alternator output now
BatteryMan
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Post by BatteryMan »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by jeremy</i>

Firstly take care with current readings on a multimeter. Many of those with a 10 amp range have no protection on that circuit and will blow if overloaded. If you suspect a leakage then start testing with a bulb in series with a battery connection and if that doesn't glow brightly - then use your meter on an appropriate scale.
Leaving a battery discharged won't do it any good but I wouldn't expect 7 volts over a few weeks to be a terminal problem. If the battery was weak - well that may all combine to finish it off.
15 - 16 volt charge form a normal alternator suggests the regulator on the alternator has failed. The effect will be to make the battery gas and need topping up as well as causing the plates to disintegrate due to excessive gassing breaking up the spongy lead. It will also overload the rest of the car circuits and will shorten bulb life and could damage some of the electronics. A corrrect reading would be about 14.6 volts.
Presumably if the relay has been installed correctly the effect is to isolate the sound system from the rest of the vehicle electrics. As both batteries have discharged more or less completely over the same period leakage in the car circuits may not be a problem. There will of course be some standby current for the alarms etc as well as clocks.
My guess - alternator failed, main battery has run dry and will need replacing too.
jeremy
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
BatteryMan
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Post by BatteryMan »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by jeremy</i>

Firstly take care with current readings on a multimeter. Many of those with a 10 amp range have no protection on that circuit and will blow if overloaded. If you suspect a leakage then start testing with a bulb in series with a battery connection and if that doesn't glow brightly - then use your meter on an appropriate scale.
Leaving a battery discharged won't do it any good but I wouldn't expect 7 volts over a few weeks to be a terminal problem. If the battery was weak - well that may all combine to finish it off.
15 - 16 volt charge form a normal alternator suggests the regulator on the alternator has failed. The effect will be to make the battery gas and need topping up as well as causing the plates to disintegrate due to excessive gassing breaking up the spongy lead. It will also overload the rest of the car circuits and will shorten bulb life and could damage some of the electronics. A corrrect reading would be about 14.6 volts.
Presumably if the relay has been installed correctly the effect is to isolate the sound system from the rest of the vehicle electrics. As both batteries have discharged more or less completely over the same period leakage in the car circuits may not be a problem. There will of course be some standby current for the alarms etc as well as clocks.
My guess - alternator failed, main battery has run dry and will need replacing too.
jeremy
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Any lead acid battery will start to sulphate if left fully discharged - less than about 12V off load - for 24 hours or more. So finding batteries at 7V after several weeks will mean dead batteries.
The high voltage when on charge indicates a high internal resistance - another symptom of sulphation.
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