BERNER CGN1921G-0-20 Ni-cad charger destruction Log (FAIL technology)

[Kiriakos GR]

One customer gave me this BERNER CGN1921G-0-20 for repair and I discover one HUGE FAIL speaking of charger electrical design.

BERNER CGN1921G-0-20 or Powerhand CGN-1921 (by another branding) this is one 19.2V 2A NiCd charger.
Inner PCB this is GJ-27  GuangJian.

Supposedly this BERNER CGN1921G-0-20 charger was working in harmony with BERNER 19.2V 2A NiCd, until the customer choose to use AXCOM  Z-YT2000SPC rebuild battery pack (Sold in Germany).

By the first charge attempt this BERNER CGN1921G-0-20 charger  demonstrate damage at thermal protection sensor ( this is fitted at 220V side at transformer coils).
Transformer this came back in life after removal of thermal protection sensor.

Few parts at  PCB this is GJ-27  GuangJian, they were replaced by new, one 220 Ohm 2W resistor, red LED and one capacitor.
By all those maintenance steps this charger came back to life and everything seemed as normal.

By starting a new charging test in my workshop and in about two hours time the room started filling with fumes and battery pack suffered from extreme over heat.
This is totally unexpected situation and I become mad, because I have now the obligation to discover of what got wrong, and to also inform my customer about the bad news.

By taking apart the charger and by making measurements, I did the discovery that this transformer alone at 225V input this was delivering 22V AC.
Those 22V AC  after conversion to DC  this was an output of 30V DC this feeding this 19.2V (nominal) battery pack.
Technically, charging voltage for such a pack this is about 25V Max and Not 30V.
   
In summary this product design it is HUGE FAIL, and my recommendation to all, this is you to stop using this battery killer, and you to find a replacement charger from a known brand. 

 

[Kiriakos GR]

Wireless Ni-Cd charger .. GREEK patent !! 

Schneider Electric ABL7RM24025   24V DC 2.5A  ( Regulated 22.2 ~ 30V )

By this power supply I am confident that some one with identical skills as I have, he will solve the over-voltage problem for good.
And by this idea you can use regular ( cheap Ni-CD rebuild packs ).

Analog ammeter this replacing LED lights, with it you have true picture of battery status.

This is my best workaround for offering an solution.
Wireless = no cables assembly yet.     

[Kiriakos GR]

First tests !!!   

[Kiriakos GR]

Comments about this Schneider Electric: ABL7RM24025 24V DC 2.5A PSU

They are product details at small print (specifications)  which someone should take in mind before using this PSU in a charger application.
This PSU when consumption ampere are higher than what this can give, then this activates a tripping mode.
PSU load check this is working due voltage detection circuitry, and if output voltage under load this is below 19V, then tripping occurs.
Tripping translates to ON-OFF cycle every two seconds, additionally this translates that battery under charge, this receives charge but not constantly in the beginning. 

Inside this battery cage there is a new battery pack of average quality Ni-Cd, I did the decision to lower charging voltage at 24V,  so thermal effect at fully charge this to be minimal.

 Because of ammeter I am able to see PSU tripping and this is annoying to watch, in the positive side of things tripping this is made electronically ( no relay clicking).

In my application this PSU it does the job, it is protected from damage, and internal electronics control this is very advanced.
But in this setup the new way of operation this is much different of what you will expect by previously using an transformer.
 
In summary, the charging mode starts with pulsing charge every two seconds (current spikes), as soon voltage gets higher and higher, current spikes duration this increases, as soon the load becomes acceptable, then the PSU it does deliver constant current at 2.4A.
Eventually battery pack this gets full progressively, at 24V charging voltage, lowest current becomes about  300mA, and about two hours later, battery packs starts having thermal effect ( gets slightly warm) and requires about 450mA in this condition.

My thoughts: I am somewhat happy because I did manage to offer one solution that it works to my customer,  but I am not totally happy of this combination with ABL7RM24025.
Due lack of other alternatives in the form of new Ni-CD charger for this tool, I would convince my self so I to consider the result as acceptable. 

Regarding assembly, I did a spectacular job, those pictures are my proofs.