RAC 6v /12v vehicle battery charger

[dull spark]

HI everyone, feeling my way on this charger it blows the fuse on the secondary side, if i connect it to a 12v battery, that happens even before i switch on at the mains, any advise very welcome.
thank you.

 

[Resqueline]

That'll happen if you either connect +/- wrong, or if the rectifier is shorted.

 

[dull spark]

schottky diode, not sure.

HI all, cant find info on the net it looks like a rectifier diode, No70T03 GP,bottom row 643441.
I am new to this to this science, Hard to learn an old dog new tricks, but I will try,Thank you.

 

[dull spark]

RAC battery charger

HI Resqueline, the guy who owns the charger said the charger was polarity protected,there is a red LED to warn of wrong polarity.there is also a green LED to indicate primary power on, and a charge complete LED. when i switched it on without a battery connected, nothing happened, when i connected a good 12v battery the charger blew the secondary fuse,if i solder in two new rectifier diodes it may work, is it possible to test the old diodes with my DMM,i have a good Fluke, I am long retired and took this up as a hobby i love it.thank you.

 

[Resqueline]

We could use a little more info. Case type, what it's in, where it's at, etc. Do you have it out of the circuit? What does a diode/ ohm test say?
If anything - searching for that part number it comes out as an N-channel 30V 60A MOSFET.

 

[davelectronic]

battery charger fault

Hi dull spark.
If your DMM has a diode check select that setting, red lead to anode black lead to cathode read the forward voltage drop, or use a small battery again + volts to anode - volts to cathode use a voltage dc range to read the forward voltage drop, so long as the drop is around 0.5 volts the diode is ok.
Dave.

 

[dull spark]

RAC battery charger

just some photos,i have not removed any components, will try some readings soon,i see Mouser have got this one,MBR2045CT in stock,the other one i cant find it is, 70T03GP, just checking in case i need them. Thanks again.

 

[davenn]

Agree with Res.

google points to a N-CH Power MOSFET

do a search in mouser etc for AP70T03GP or SSM70T03GP

instead of the GP suffix you can also try GH or GJ

cheers
Dave

 

[Resqueline]

One giveaway is the PCB designation being M1 while the dual diode is designated D7. So it can't be a diode, and neither can it be a normal transistor (designated Q).
I've never seen the M designation used before, but maybe it's M for MOSFET. See if it can be one of the datasheets here. Take a shot of the PCB backside too please.

 

[dull spark]

RAC battery charger

HI Dave, I have taken a reading of MBR2045 CT. it reads 0.2 ohms, on the Diode test the DMM buzzer is continuous,on anode/cathode or cathode/ anode,now no two Diode which I have failed to identify,It is giving a reading of 10,000 ohms, and the diode test is 2.3 volts. please note these are still soldered to the PCB.
Thank you Dave.

A little Knowledge is dangerous.

 

[dull spark]

RAC battery charger

HI Resqueline, some more photos, hope it helps,
Thank you.

 

[davelectronic]

Diodes

Hi again.
The average forward voltage drop of a silicone rectifier diode is 0.5 volts, your diode configuration seems as if its a Schottky Rectifier. There is a link to the PDF data sheet below.
MBR2045CT is top of the list and a 87kb size file, more info on what the readings can be found in there i expect, in circuit can alter a single components characteristics depending on where the readings are taken from.
Dave.

http://www.datasheetcatalog.com/datasheets_pdf/M/B/R/2/MBR2045CT.shtml

 

[davenn]

did you check out the suppliers for the part numbers I gave you ?

Dave

 

[dull spark]

RAC battery charger Diodes.

HI Dave, thanks for all the info,Mouser have this one,MBR 2045 CT.I am going to take a chance if they are both faulty, which i have not proved yet.this one70T03GP i cannot find,but as you say GH/ GJ may be ok and they are in stock, I will try and D, solder same and test them as best i can with Fluke, I will ask Wife to suck solder with straw some chance,HA HA
will let know how i end up, hate to see the we charger in the dust bin.
Thanks again.

 

[davelectronic]

No i am all in favour of salvage, binning is a last resort, even then i try and save reusable hardware, anyway good luck with it.
Dave.

 

[dull spark]

RAC battery charger Diodes.

Hello Dave, I have been busy trying to rewire an old tractor, I tried to order the parts for the charger but found it quite frustrating, hard to find a cross ref,or a data sheet for the n mosfet.
I have found the rectifier one,mbr2045ct no problem but they come in packs of 25, or the companys min,order by credit card is £20 plus vat plus postage. the price of the MBR2045CT
for one piece is 80 Pence. anyway Dave the 20 on this one,indicates 20 amp,and the 45 is the voltage, could I use a similar part where the nos read 30 amp, 50 volt,or say 25 amp, 60 volt? or will the wife think I have started smoking again, HA HA.

 

[davelectronic]

Hi dull spark.
I cant see a problem with that, both should be fine, but for more leeway i would opt for the 25 amps 60 volts, the old 45 volt unit and the new 50 volts is a bit close, it probably would be ok i would think, thats a lot of one components in an order most suppliers will sell single units.

 

[Resqueline]

Just observe that the higher voltage Schottky's also tend to have a higher forward voltage drop and so gets a higher power dissipation (loss).

 

[dull spark]

Thank you Resqueline, I wll try to match both modules as near as possible to the original.I am learning day by day thanks to you and all the forum members, I treat this new hobby with respect, I have read bits and pieces about the great people who invented various components that are still used every day, people who are engrossed in this science have my total respect i think modern medicine, and electronics, go hand in hand. Thank YOU.