Battery Charging Question?

[daveh_rav4]

Hi...

I have a Rav4 4.1 (1998) that I have had for a few months... my last car was a bog standard Ford XR2 (great car till it rusted away :( ). To charge the Battery I used to just chuck a Battery charger across the Pos/Neg terminals with the Battery still on the car.

Q. Is it ok to charge the battery on my Rave 4 this way? I read somewhere that you have to remove the battery to eliminate damage to the on-board electronics/PCM systems? Then again I have also read that it is risky taking the battery off as you may lose information from the on-board computer?

Any advice appreciated...

Dave

[bothwell_buyer]

Hi...

I have a Rav4 4.1 (1998) that I have had for a few months... my last car was a bog standard Ford XR2 (great car till it rusted away :( ). To charge the battery I used to just chuck a battery charger across the Pos/Neg terminals with the battery still on the car.

Q. Is it ok to charge the battery on my Rave 4 this way? I read somewhere that you have to remove the battery to eliminate damage to the on-board electronics/PCM systems? Then again I have also read that it is risky taking the battery off as you may lose information from the on-board computer?

Any advice appreciated...

Dave

Hi Dave. I found the problem with disconnecting the Battery was that the alarm had to be reset. If everything is switched off, I don't see how a charger could affect anything...but someone here may know otherwise. I did find that the Battery on the RAV doesn't last very long at all. They are small, and seem to have a drain on them by the alarm system or whatever else. I'd be lucky to get 2 years out of a Battery.

Nowadays, I think there's a range of high quality batteries available, but no idea about cost and of course we're back to availability as it is so small compared to most cars. The other thing is using a trickle charger if its convenient.

Thankfully up to now, the alternator has worked well and coped with the light array. With the replacement engine, I'll need to see if the alternator is up to it....

Ian

[anchorman]

Yes trickle charge for a minimum of 12 hours - preferably 24.

The normal recommendation is to disconnect the negative lead to avoid spiking the electronics but I have never tried otherwise. If bothy has and got away with it then I bow to his experience. I would always connect the positive first then the negative to a good earth away from the Battery. This avoids the risk of a spark from igniting the explosive gases from the Battery. Only when it is connected should you turn the charger on as this also reduces the risk of a spark and any arcing which can kick the current enough to damage the alternator diodes and transistors.

[shcm]

Hello Dave,

These two oracles are of course right as usual :D.

If it's trickle charging (a constant voltage supply), then you should get away with it. I've done it myself.

To charge a lead acid Battery in theory it's something like charge at constant current at C/4 (C is Battery capacity so if it's 100Amphours the charger pushes - or tries to - 25Amps into the battery), then after the Battery has reached a certain voltage it's C/10 for a bit, then finally to a constant voltage trickle charge.

I'd be more wary of constant current charging, but even then I'm probably being unnecessarily cautious as the battery should hold the terminal voltage below about 14.7V anyway.

It varies from manufacturer to manufacturer, but, just to reassure you if you've got ECUs that have a permanent battery feed - most OEM ECUs for a "12V" car are design to take 18V for at least one hour (that generally means forever!) and 24V for a few minutes. It simulates a gorilla trying to jump start it with a European 24V truck battery. Not that I recommend you do that - I wouldn't!

Oh, and with the engine running, there is a little thing called "load dump" which simulates the battery being disconnected (or possibly jump cables being disconnected) and the resulting alternator output having a small fit. That can be 80 to 120V for something like 40ms to 400ms depending on the vehicle/alternator. It can punch holes through badly designed ECU power supplies like a knife through butter. OEM ECUs are designed to take this, but I have my doubts about some of the aftermarket stuff I've seen.

Of course components can age, so just take care and of course it's all at your own risk :D

Cheers

[bothwell_buyer]

Hello Dave,

These two oracles are of course right as usual :D.

If it's trickle charging (a constant voltage supply), then you should get away with it. I've done it myself.

To charge a lead acid battery in theory it's something like charge at constant current at C/4 (C is battery capacity so if it's 100Amphours the charger pushes - or tries to - 25Amps into the battery), then after the battery has reached a certain voltage it's C/10 for a bit, then finally to a constant voltage trickle charge.

I'd be more wary of constant current charging, but even then I'm probably being unnecessarily cautious as the battery should hold the terminal voltage below about 14.7V anyway.

It varies from manufacturer to manufacturer, but, just to reassure you if you've got ECUs that have a permanent battery feed - most OEM ECUs for a "12V" car are design to take 18V for at least one hour (that generally means forever!) and 24V for a few minutes. It simulates a gorilla trying to jump start it with a European 24V truck battery. Not that I recommend you do that - I wouldn't!

Oh, and with the engine running, there is a little thing called "load dump" which simulates the battery being disconnected (or possibly jump cables being disconnected) and the resulting alternator output having a small fit. That can be 80 to 120V for something like 40ms to 400ms depending on the vehicle/alternator. It can punch holes through badly designed ECU power supplies like a knife through butter. OEM ECUs are designed to take this, but I have my doubts about some of the aftermarket stuff I've seen.

Of course components can age, so just take care and of course it's all at your own risk :D

Cheers

An here's me thinkin an oracle is an old Orcadian round boat!

[shcm]

An here's me thinkin an oracle is an old Orcadian round boat!

Nah, very small unstable looking fishing boat ;)

[daveh_rav4]

Thanks for all the advice guys... I took the bull by the horns and charged the Battery last night. I have an Absaar 12/6 volt fast/normal charge charger... carefully attaching the charger with ignition and everything switched off (inc. the alarm), I slow charged the Battery with it still connected to the vehicle for 20 hours. All worked out ok; Battery appears to be up to full par now and no apparent side affects to the Rav!

Its just that in this cold weather and extra use of lights, lots of short trips... the alternator can't quite keep up with the load, so this slow charge cycle has done the trick... what a great forum this is, with so many knowledgeable Rav'ers

I agree that the battery on my Rav does appear to be physically small I think its a 65amp hr... if when the time comes to change it I shall obtain a higher capacity, i.e. 95 amp hr or so... B)

DaveH

Hello Dave,

These two oracles are of course right as usual :D.

If it's trickle charging (a constant voltage supply), then you should get away with it. I've done it myself.

To charge a lead acid battery in theory it's something like charge at constant current at C/4 (C is battery capacity so if it's 100Amphours the charger pushes - or tries to - 25Amps into the battery), then after the battery has reached a certain voltage it's C/10 for a bit, then finally to a constant voltage trickle charge.

I'd be more wary of constant current charging, but even then I'm probably being unnecessarily cautious as the battery should hold the terminal voltage below about 14.7V anyway.

It varies from manufacturer to manufacturer, but, just to reassure you if you've got ECUs that have a permanent battery feed - most OEM ECUs for a "12V" car are design to take 18V for at least one hour (that generally means forever!) and 24V for a few minutes. It simulates a gorilla trying to jump start it with a European 24V truck battery. Not that I recommend you do that - I wouldn't!

Oh, and with the engine running, there is a little thing called "load dump" which simulates the battery being disconnected (or possibly jump cables being disconnected) and the resulting alternator output having a small fit. That can be 80 to 120V for something like 40ms to 400ms depending on the vehicle/alternator. It can punch holes through badly designed ECU power supplies like a knife through butter. OEM ECUs are designed to take this, but I have my doubts about some of the aftermarket stuff I've seen.

Of course components can age, so just take care and of course it's all at your own risk :D

Cheers

An here's me thinkin an oracle is an old Orcadian round boat!

[chatman]

Ha wait till you try and charge the Battery on the 4.2 model.... :censor: :censor:

For one you cant get to it easy as it's behind a screen and under the front screen area...You have to remove some trim with fiddly screws then you can get to it.....