Battery Chargers DOA Model HF #45005

Hello gang!

Recently I purchased two 6/12 volt battery chargers with 2 and 6 amp modes at EBAY. A liquidator was ditching for Harbor Freight, made by Chicago Electric. Retail is $60 for both and I paid $19 for both including shipping knowing that both were not working. Thought I could get at least one if not both going and now am having some problems. Manual states they don't sell replaceable parts, and I have at least one bad part. The diode in the bottom right corner of first BAT charger (see pic of circuit board) gets very hot when plugged into mains for a few seconds with battery attached. The board has two diodes labeled scr1 and scr2, and they are stamped as BT151 25J TRANSUN. Ebay sells similar SCRs for $4 including shipping. I suppose I could swap good diode from other charger but that one works fine.
The second charger was also DOA originally. Noticed that there was no continuity on one of the primary leads so I moved to a different lead and now secondary output tests ok so one charger appears to be working already.


Woody

 

mystery component

Just thought of another question. If I peel back a layer of tape wrap on the primary there is a mysterious little rectangle box like device that I can't ID. The photo is a little shaded but on the top of this thing on either side there are two wires coming out of it. One attaches to the first of five primary leads and the other attaches to the last lead. As far as I can tell it just links both leads electronically. But there is no continuity between first and fifth lead. Also the first lead has no continuity between any of the other leads. What is this item?

Both chargers were DOA, so to power them, I shifted the AC black mains live lead (moved live ac wire from 1st to 5th lead). The only thing I can think of, is that the wire has a bad connection to 1st lead on both battery chargers. This liquidator is selling these things by the truckload so I think there is definitely some quality control issues going on with these units. Most are being resold as working units, but a ton of them have also sold in pairs of two as not working.

Woody

UPDATE: As Dave explains below, this unkown item is a fuse between lead 1 and 5 that blew on both my chargers. If yours blew, the fuse should be replaced as it protects the transformer. I did not know there were any marking on it but when I clipped it off markings became visable with a mag.glass. It is rated at 2amps 240 volts and blows @ 130 centigrade.

 

Dave, thanks for the welcome -great site you Aussies have here!

Since my primary taps are open between taps 1 and 5 then I assume fuses on both chargers blew. I have several spare regular fuses on hand ranging from .2 to 30 amp -can I use one of these fuses to replace and what size would you recommend?


Cheers,
Woody

 

Quality Control @ Chicago Electric

UPDATE...

I removed the board to examine with a glass, and noticed that two different, smaller power diodes were accidentally soldered together. A brief hot touch with hot solder wick remedied that problem. Now when I plug AC cord in, there is no smoking hot diode, and there are normal secondary transformer readings. HOWEVER, when I add/connect it to a live battery then the same large diode is still smoking hot.


Woody

 

Before I order some diodes that may or may not even work, I remembered a "small" detail that I definitely should have mentioned. The attached pics show that the transformer on the non working BAT charger may have some shorted windings. Notice how the yellow wrapping around the primary windings looks like they may have melted a little.

As previously stated, when I plug charger into mains, the secondary voltages are all good, but when a car battery is connected to DC output then that larger diode still gets very hot. The transformer does not get hot with just AC connected, and does not get hot with BAT added -though I only connected battery for a few seconds. Could this transformer be toast, and how do I test to see if it's toast?


Woody

PS for some reason could not post 2 pics and will try at another time, but wrap looks to be partially melted.

 

melted plastic wrap pics attached -toasted or ready-to-be toasted transformer?

 

Unidentified cracking sound ?

Not sure if I mentioned this fact or not -- as per manual instructions, I hook mains AC first to charger then DC clips to battery. Now on mine, I always turn it off after a few seconds after battery connected because there is a loud cracking sound every time. Do you think that cracking sound is coming from the transformer or the hot diode?

Woody

 

Steve, thanks for your reply again. I don't have any such resistor, but I have many old car dome light type bulbs. Okay if I "charge" bulbs as the load, and should I wait until new diodes arrive to test?

Jotto, thanks for the reply also. I have ordered new high voltage SCRs. The bad diode had continuity in any direction tested with a multimeter on the diode setting. The good diodes tested with ohms in one direction and infinite resistance in two other directions. So I'm guessing that one diodes is toast and can no longer block voltages from a live car battery, and this is why when battery is connected diode gets ultra hot? Also not sure of SCR's amp rating of old, but new ones have 12 amps continuous duty.

Since both boards are identical, I tested all twenty some components to see if anything else was wrong:

1.The two smaller diodes test same on both boards
2. All the resistors were within 10% tolerances
3. Three unknown transistors test the same
4. One of four power transistors on the good circuit board tested "leaky" -when compared to same measurement on the other board the good power transistor showed infinite ohms when tested in the diode mode. Of the eight total power transistors this was the only one that tested leaky and it is located on the charger that works.
Now I'm wondering if I should order a replacement power transistor. Ebay sells generic power transistors. Not sure if they will work, and if all four should be replaced??


Woody

UPDATE: I found some numbers on back of power transistors and ordered exact replacement. Interestingly, three of the four power transistors on the two boards are different models. The one that is leaky has only 40 volt max transistors, while the other board has all 150 volt maximum capacity.

 

Thanks for noting mistake. I highlighted and corrected in above post to 40 volt and 120 volt. Looks like this charger needs to see voltage from battery before it will output amps. Anyway to override this safety feature?

 

If anyone ever wants a picture of how board is supposed to look like here are pics front and back. It is complicated circuit having 13 resistors, 4 power transistors, 3 regular transistors, 2 SCRs, a pair of 1n4007 diodes, and a voltage regulator diode. Part numbers are on each component.

 

Steve, understood what you said the first time -the fuse/light would blow if amps were too high thereby protecting BAT and charger. What my question was, and I admit it was not at all asked very clearly, how to override the safety feature by altering the circuit board? This would be useful if using charger for another purpose like a power supply for bench testing or electroplating. I suppose easiest way would be to bypass circuit board completely and take voltages directly from the transformer, then bridge rectify it, and somehow use caps/resistors for smoother DC?
Today I took voltage measurements on this center-taped secondary and found six different voltages ranging from about eight to 25 volts, and was thinking this could make a nice "stepping" power supply, especially since I have an extra one. Any suggestions on moding this to a PS?

Thanks,
Woody

 

Steve, the SCR diode finally arrived and has been replaced. When tested on a spare shorted 12 volt battery, the charger seemed to function just like the other working battery charger (it chargers until reaches 14.4 volts, then turns off until it falls to 13.88 volts, then restarts charging, and it loops this process continuosly). So at least it appears to be working now.
Any luck deciphering the diagram?


Woody

Note: 2 amp setting is better for temporarily maintaining a battery once it starts maintenance cycle.