SIMPLE BATTERY CHARGER

[ianmoore]

Hi!

Ive just made myself a controller for a charger that auto detects when the battery is at a preset voltage and switches off a charging circuit...

this all works fine with on board micro controller LCD screen...nice

HOWEVER... it basically opperates a relay that will turn the charging circuit on/off

I got a 1000 watt tranformer..... straight onto a bridge rectifier and then onto the batteries....
It gets hot quick!

the battery bank is 60volts
the 1000 watt transformer is 45volt+45volt =90volt

I guess the charging voltage is a bit high.... maybe

but my main question is this...
will this charge the battery ok.... a tranformer onto a bridge rectifier and then onto the battery?

or am I missing something? a choke?another diode? do I need a smoothing capacitor for battery charging?

thanks for your help

[ChrisB]

Hi Ian , sounds like you are pulling a bit too much current to be honest.

You dont say what batteries you are charging Flooded LA's sealed LA's Nicads etc etc

Flooded LA's should be fine with a tranny and a bridge , others need a bit more.

Need a few more details on types of batts etc Ah etc and voltage I assume you are using 12v mono blocks or similar ??

90volts on a 60volt pack sounds a bit high to be honest ??

Dont forget it will charge to the peak of the sine wave rather than the RMS voltage

Need a few more details before going further, and I wouldnt mind seeing the controller and having some more details as it sounds quite nice.

ChrisB

[Peter Eggleston]

90 volts onto a 60 volt pack will be OK at first but you will not be able to fully charge your pack like this. Once it is about 80% charged, the current supplied will be too high for the battery to take and it will gas severely. What I do at this stage is change to a smaller charger. In my case a variac/bridge rectifier charger which supplies 8 amps at about 70 volts, which can be varied until the pack is fully charged when it will again start to gas.
In my case it is important not to let the batteries gas as I use lead gel batteries which are not topped up with water.
Peter

[ChrisB]

90 volts onto a 60 volt pack will be OK at first but you will not be able to fully charge your pack like this. Once it is about 80% charged, the current supplied will be too high for the battery to take and it will gas severely. What I do at this stage is change to a smaller charger. In my case a variac/bridge rectifier charger which supplies 8 amps at about 70 volts, which can be varied until the pack is fully charged when it will again start to gas.
In my case it is important not to let the batteries gas as I use lead gel batteries which are not topped up with water.
Peter

Exactly Peter if Ians running say 5 x 12v pack then if we are talking about say a cyclic charge voltage of max 14.8ish for Flooded LA's then the top charge voltage is going to be something like 74 volts, now your trying to get 90volts into it so the currently will max out very quickly on the tranny and the bridge from first connection and hence your problem with it trying to cook the tranny and the bridge.
Also theres the issue that it even if you are seeing 90voltsDC off the bridge I guarantee you that it will actually try and charge the batts to at least 130Volts DC as it will use the full sine wave rather than just the RMS AC voltage. I found this out when using a 110v supply to charge a 120v back of batts, it would quite happliy charge the pack to 150v even though if you unloaded the tranny it measure just 108vDC once the battery was connected it would quite happliy charge the pack to 150v due to it using the full sine wave.

Your 90v set up could see the pack voltage up at 130vdc and hence your cooking problem.

A vairac or some sort of current limiter really is your only way ( thats if you've got Flooded LA's ) or voltage controller if you've got Gel bats like Peter

ChrisB

[electricvehicles]

I admire you for making your own charger, sounds very interesting.

Just a small pointer -- In my experience and also as advised by all the battery manufacturers. The best charging method for flooded PB batteries is a straight forward taper charge charastic. whereby as the battery voltage increases the current decreases. Before the advent of using thyristors transformers were wound in such a way as to taper off the current. Thats why we are always repairing thyristor controlled chargers. Transformers on these are more or less constant current and as such the thyristors have to do most of the work

If I was using a transformer with a taper charastic I would set a basic controller as follows: Gassing voltage at 2.35V per cell so a 72V battery would be set up at 84.6V and the timer set to run for a further
4 hours ( gassing time )

If I were using a controller with proportional gassing, whereby the gassing time is relative to how long the battery has taken to reach the gassing voltage one would only need to set the gassing voltage up.

Hope the above has been of help

Please let me know what battery type you are using and their AHC @ 5Hr rate.

If you do need any further info or perhaps some literature regarding charge controllers pls let me know.
Good luck with it
Regards
Dave

[ianmoore]

Hi Thanks for the replies,
lots of info to munch my way through... cool!

the batteries are simply...110 amp leasure/Marine batteries... don't laugh!
its all I can afford right now for my first battery set.

I guess from the sound of it I could use my variac which is rated at 8 amps... (not sure I belive it)

at first I tried charging the 60volt battery bank with my variac ONLY and a 30amp bridge rectifier.

when the voltage was set to 80 Volts it charged at about 2 to 3 amps

however the variac got hot and smelly after about 40 mins.

I now have a 90volt toroidal transformer (45v+45v)
onto a 30 amp bridge.

this just blew a 13 amp fuse on the mains input side!.....
I guess my bridge rectifier must have just frazzled... and hence the apparent short circuit....mmmmmm better heat sink I think.

anyway... it looks like the best thing to try is the variac...followed by the 90volt transformer and then the 30amp bridge with a good heat sink.

I guess I only need to turn it down a little....

then if need be I may be able to take a few turns off the torroidal transformer to bring its voltage down to 80-85 volts
does anyone know if the secondary turns on a toroidal transformer are wound on top of the primary 240v coil...... I hope I dont have to unwind the primary first to get at the secondary.

any other suggestions? do I need any smoothing capacitor for charging?
(I'm not used to these voltages and currents...)

[aminorjourney]

It'd be really useful if you could give us all the battery spec sheet. Different lead acid batteries need different treatment and it's important you don't charge them in an incorrect manner for the ones you have. I know from experience that it's easy to kill one sort of Lead Acid battery with a charger designed for a different type!

Nikki.

[ChrisB]

Daves spot dangley on by the looks of things Ian, but I have only whizzed through his post.

No need for smoothing caps what so ever with flooded LA's

Not sure about unwinding a tranny mind you not something I would attempt TBH

I'd play with a vairac first and find the setting you need and then find a tranny to match it

As Nikki says using the wrong charge on the wrong battery can cause lots of probs BUT Flooded LA's can take quite a bit of abuse, where as sealed or gels are REALLY fussy.

ChrisB

[ianmoore]

Unfortunately no data on the batteries.

they are flooded and have a plastic screw on top to refill them.
they also have a viewing hole for top up level(well I guess that is what its for anyway)


very similar to these


http://www.tayna.co.uk/getimage.php?image=2235numax-l110.jpg

[aminorjourney]

Excellent. Can you have a look at the plates inside? (Take one of the vent/filling covers off and have a peek) Are the plates straight or curved?