SCR Equivalent component (not sure)

[lilimike]

I want to build this SLA charger.
As a replacement component for the MCR100-6 I was given an 2N5064 but starting with their descriptions and comparing the data sheets I am not sure this is an equivalent component.
Can anyone comment on this please?

Thanks

Mike

 

[lilimike]

I tried it and it works ok.
The replacement SCR gets a little hot so I will add a heatsink.
Also like the writer of the circuit indicates the transformer gets hot or I should say really hot like "untouchable" so I will also add a fan.

Thanks to everyone who helped out in this thread...

If anyone have a better suggestion for a circuit that can charge a 12V SLA battery with a security feature that prevents from overcharging that would be great, I find there is too much heat in this circuit.

Mike

 

[MikeMl]

When building a charger for SLA's, I put a small 24V (5W) or two 12V (3w each) in series with the 120V primary of the transformer. That provides current limiting (ballast) when the charger is connected to a mostly discharged SLA, protecting both the SLA and the transformer. As the battery accumulates charge, the current drops, the filament in the bulb cools, the resistance goes down, so the current is sort-of regulated.

 

[lilimike]

Based on what you are saying, the transformer should get hot only when the battery is mostly discharged?

Maybe I have other issues, I have a 12V 4AH that was at 11V (with no load) I connected it to the charger and after about a couple of hours the battery was at 12.8V but I stopped because the transformer was too hot. I don't think it would have made it up to 13.8.
In the circuit they propose a 12V .5A transformer but I am using a 14V .5A, could this be the cause of my issue?

Thanks

Mike

 

[MikeMl]

Based on what you are saying, the transformer should get hot only when the battery is mostly discharged?

Leave the battery disconnected, and leave the charger plugged in for a few hours. The transformer should get only barely warm to the touch.

Maybe I have other issues, I have a 12V 4AH that was at 11V (with no load) I connected it to the charger and after about a couple of hours the battery was at 12.8V but I stopped because the transformer was too hot. I don't think it would have made it up to 13.8.
In the circuit they propose a 12V .5A transformer but I am using a 14V .5A, could this be the cause of my issue?...

Yes, the transformer should be sized just right. I have built several SLA chargers using wall-wart transformers. These are usually built with loose coupling between the primary and secondary windings (core air gap?) to protect them from overload and catching fire. If I try to use a "better" transformer, I have run into the transformer overheating issue when the battery is deeply discharged. That is where I add the ballast lamp(s) in the primary side.

 

[MrAl]

Hi,

That circuit looks like a lot of parts/trouble just for 350ma charge current. How about an LM317 based design with just a few components?

 

[lilimike]

I had 3 goals:
1 - To recharge a 12V SLA battery
2 - To not worry about overcharging
3 - To have some way of knowing the battery is fully charged without using a voltmeter.

This circuit fulfilled all of my goals and it does have a few parts but it took only a couple hours to build including redrawing in Eagle and PCB making so it was not so bad.

I found a 24V transformer with a center tap which seems to be much cooler, I am recharging my battery at the moment and I think with Mike's solution to add a light bulb if it gets too hot it should be working fine.

Mike

 

[lilimike]

That 24V transformer I have is not getting hot at all, barely warm. It's been connected for 3.5 hours and it recharged a 12V 4AH battery from 12.53V to 12.73V during that time. I find it's not going fast enough so I tried to measure the current but when placing my meter in series with the charger it will not trigger the SCR so no current is going through when I use the mA scale. Trying the 10A scale works and I get 70mA and I am thinking it is probably not exact because the scale I am using is too high however it is no where near what I am expecting which is at least 300mA so I figured my transformer is not powerful enough. It is an old transformer I took out of one of my first projects dated 1986, it is all covered with metal and it has the following markings on it:
SP-200-19
UU2-300
26U7ZE
It has the name Zebra on it. Don't bather searching on Google, you won't find anything useful.
Anyways is there a way to test what's the maximum current a transformer can generate and I guess apply a % to determine its rated current?

Mike

 

[MrAl]

Hi,

The main test would be to see that the transformer doesnt get too high of a temperature rise. You would connect the transformer with no load and let it sit for say overnight, then measure the temperature. You would then load it with some load and let it sit overnight again and measure the temperature and that will tell you the temperature rise.
You probably dont want more than about 40 deg C temperature rise with any load.

If you can see the secondary windings you might be able to tell what gauge wire they used, and that will tell what the output current can be.

 

[lilimike]

Unfortunately the transformer is all covered with metal so I can not see any windings.
This transformer is 24V with a center tap and It is the same size as another transformer I have that is 14V 500mA with center tap.
A night of sleep made me realized that what I said in my previous post doesn't really make sens, if it was not powerful enough it would get too hot rather than just supplying lower current?
Anyways it has been recharging my battery for the past 19 hours, when it started the battery was at 12.53V and now it is at 13.09V and the transformer is about the same temperature as my forehead, maybe even a bit cooler.
I am presently using the center tap to get the 12V needed but I was wondering if I would get more current when recharging the battery if I used the 24V in series with a cap to reduce the voltage to 12V?

Mike