repair of battery charger

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a.bisnath

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Electrical worker
Battery charger for 220volt d.c. battery bank electronic board controls charging,board has fried-no coming back,thyristors are tested and good,can I make a simple circiut to keep the gate switched on and maually with voltmeter and ammeter switch off unit when charged?
cost of card is cost of new charger,need temporary solution ,asap ,unit used on plant in remote caribbean area limited acess to options
 
I wouldn't just wire the gates on as the circuit was probably firing the thyristors as an active rectifier. If you just wire them on it may short the battery directly to the line and let more smoke out.
 
090320-2055 EST

You can turn on an SCR easily with a 100 ohm resistor from anode to gate. This will turn on at a few volts anode to cathode. If these are back-to-back SCRs, then do each the same. If it is a half-wave rectifier, then you need a diode from anode to the resistor instead of directly connecting the resistor to the anode. The PIV of the diode has to be large enough to substantially exceed two times the peak of the applied AC voltage. If the SCRs are used in a full wave center tapped circuit, then the diodes in series with the 100 ohm resistors are required just the same as in a half wave only circuit.

If most current limiting was done by phase shifting the turn on of the SCR, then you may need to add external series current limiting between the combination of SCRs and rectifiers.

If you are using the word thyristor for some device other than an SCR, then you have to provide more information.

There should be no real need for a 1 W resistor, but use one of this size. Note: as soon as the SCR turns on the voltage across the 100 ohm resistor is very low. So there is very little average power dissipation in the resistor. This turn on will occur very shortly after the zero crossing is passed.

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With a 220v battery bank I would not be too comfortable with bypassing the control circuits.....you MUST consider the possible explosive consequences of overcharging that battery bank.

And if the board costs as much as a whole charger..replace the charger. How do you know that the rest of the charger is o.k. and won't fry a new board?

As I have said here on many posts in regards to trying to save money on a quick fix, you must first consider the potential costs in terms of damaged equipment, lost productivity and potential injury or death of personnel before trying to save a few bucks on a quick fix.

Order a new charger and have it shipped overnight or air freight and don't take potentially fatal risks.
 
a.bisnath said:
Battery charger for 220volt d.c. battery bank electronic board controls charging,board has fried-no coming back,thyristors are tested and good,can I make a simple circiut to keep the gate switched on and maually with voltmeter and ammeter switch off unit when charged?
cost of card is cost of new charger,need temporary solution ,asap ,unit used on plant in remote caribbean area limited acess to options
Click to expand...
Not a good idea.
I assume the batteries are either wet cells (Plante) or VRLA.
Internal impedance is low. The thyristor bridge will have some operating margin on voltage to allow for control and supply voltage variation.
Convert the bridge to effectively an uncontrolled diode rectifier won't allow for those voltage margins. You will overvolt the battery and excessively high will result.
 
gar said:
If you are using the word thyristor for some device other than an SCR, then you have to provide more information.
Click to expand...
Thyristor is generally the term used in UK to mean the same device that you would call SCR.

Turn on by an anode to gate resistor generally isn't a good idea.
 
mxslick said:
With a 220v battery bank I would not be too comfortable with bypassing the control circuits.....you MUST consider the possible explosive consequences of overcharging that battery bank.

And if the board costs as much as a whole charger..replace the charger. How do you know that the rest of the charger is o.k. and won't fry a new board?

As I have said here on many posts in regards to trying to save money on a quick fix, you must first consider the potential costs in terms of damaged equipment, lost productivity and potential injury or death of personnel before trying to save a few bucks on a quick fix.

Order a new charger and have it shipped overnight or air freight and don't take potentially fatal risks.
Click to expand...


Five stars right there mxslick:wink:
 
090322-2218 EST

Any battery charger will consist of a voltage source that supplies the energy to go into the battery, a current limiting element or elements, and the battery being charged. The battery is essentially a constant voltage device.

Any normal battery charger, whether diodes or SCRs are used for rectification, will have an internal impedance that is probably designed to limiting the system charging current to the designed maximum current, or somewhat above.

In an active system where SCRs are used to modulate the charge current toward the end of the cycle you will probably find that the SCRs are on nearly full cycle during the initial charge.

a.bisnath's plan was to monitor charging and shut it down when the voltage reached a certain level. Also note that I suggested that maybe additional current limiting impedance should be added as a precaution.

It will be interesting to hear what solution was used and what was the result.

.
 
gar said:
090322-2218 EST
In an active system where SCRs are used to modulate the charge current toward the end of the cycle you will probably find that the SCRs are on nearly full cycle during the initial charge.
Click to expand...
For lead acid cells which is probable for a 220V system, charging is usually at constant voltage, typically 2.27V per cell at 20 deg C.
To get constant voltage out of an SCR charger means constant conduction angle throughout the charging cycle all other things being equal.
There has to be enough headroom to allow for changes in supply voltage, a control margin and, if included, temperature compensation. With those margins, full output with the SCRs phased fully on would be capable of significant overvoltage and no current limit. Not good.

Yes, you could put a series resistor between charger and battery. But that still leaves the problem of turn on using anode voltage. It produces a poor gate drive signal with a very slow rise time which can result in SCR failure. Again, not good.

I'd strongly advise against going down this route.
 
my idea

my idea

made small 5 volt d.c. power supply from small transformer,bridge rectifier and capacitor used 500k pot to get value of voltage that will ,when impressed on thyristors in bridge arrangement will keep them on and they should act a diodes,manually monitor at frequent intervals volts and amps,shut off or put on trickle charge resistor as neccessary
 
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