Onboard charger repair. Value of ZD?

[Bigrockk]

I have a Schumacher-SS-15A3-OB three bank onboard charger that has failed. It is usually permanently mounted in my boat to keep two trolling motor batteries and the starting motor battery charged.

The obvious findings so far are the internal fan has seized and ZD1 has failed. I have included pics below.

Is there any way to determine what the value of ZD1 should be, the markings can’t be read anymore.

I am not an electronics person, just a retired electrician that likes to dabble and repair my own stuff when possible. I get the feeling I’m out of luck without the data sheet/schematic but thought I would ask here first.

 

[Sunnysky]

Service manual is likely to be non-existent, certainly a proprietary document.

J1 function may give the clue for voltage.
With 220 Ω connection to 12V to bias the Zener and the power limitations of both parts, it is likely for some off board function that needs a lower voltage like 9V or 5V.
I believe the cathode has lower thermal reistance, the part overheated enough to melt solder on that end and may have been due to overvoltage. Normally if it was say a 5V Zener, the 220R part would conduct <40mA to the load and Zener, so that even with no load, the Zener would never overheat, unless the 12V side was significantly greater than 15V.

of other concerns ... the big cap is bulged and ,likely defective, which may have triggered the failure in the Zener.

 

[davenn]

Is there any way to determine what the value of ZD1 should be, the markings can’t be read anymore.

hi welcome

yeah, it's going to equal the output voltage of that connector and you can tell us that



Dave

 

[Bigrockk]

Thanks for the replies guys,
The J1 connector is for the internal cooling fan which failed, the fan is rated at 12v and 1.6 watts. I removed the fan to repair it, and forgot to include it in the pics.

Sunnysky- I noticed the bulging cap as well but when you press on the black plastic top it just springs back and forth and doesn't feel like anything underneath it forced it up, I don't have enough experience to know if this is common, maybe I should just go ahead and change it as well?

I did contact the manufacturer for info but no luck with that yet.

Just to add a little more info, the failure started out with the charger indicating battery 2&3 were fully charged (green indicator light) but # 1 would always show charging (amber indicator light).

I then switched the #1 and #2 charging leads thinking maybe the #2 indicator would now show it was always charging if I had a bad battery. No luck, after that #1 & #2 would always show charging.

I realize I may never get this working right but it is kind of fun to try.
Appreciate the help!

 

[Sunnysky]

The bulged cap,is from out gassing due to excess heat and ESR which degrades performance. and causes spikes in voltage from current pulses.

A 12V fan then implies a need for a 12V Zener. The fan represents 1.6W/12V=133mA. or Z= 12V/0.133A= 90Ω. Now the 220 red-red-blk is actually a 22Ω part which makes more sense now.

http://www.digikey.com/product-detail/en/fairchild-semiconductor/1N4742A/1N4742AFS-ND/977257

Pick cap to match from here
http://www.digikey.com/product-search/en/capacitors/aluminum-capacitors/131081?k=&pkeyword=&pv7=3&FV=fff40002,fff80009,6540013&mnonly=0&newproducts=0&ColumnSort=0&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25

 

[Bigrockk]

Thank you "Sunnysky". Great stuff, and much appreciated I will get both the cap and the Zener changed and report back!

 

[Bigrockk]

Quick question, I'm sure I have missed something here but the link to the Zener is for 1 watt, should I not order one that is closer to the wattage drawn by the fan?
Hope you don't mind the questions, I am pretty green at this!

 

[Sunnysky]

assuming Ohm's Law
(14.2V -12V)/22Ω=100mA thus 1.2W when fan is unplugged or fails then zener fails.... hmmm sounds familiar
Yes get bigger Zener

So Zener is equivalent load => 12/14.2V = Rz/(Rz+22) ...Rz=120Ω

Meanwhile Fan 1.2W=V^2/Rf so Rf=173Ω, so when fan is connected the Zener draws much less current taken by fan.

So if fan fails open circuit, Zener fails.

 

[Bigrockk]

Thank you again for the great info and your patience Sunnysky, much appreciated!

 

[Sunnysky]

Zeners regulate by always drawing more current than worst case load, so that at no load, it can survive and full load still draws enough current to limit voltage swing.

 

[Bigrockk]

Well parts are on order, hope I got it right. Really enjoy the explanations and the math, it really makes it possible for someone like myself to gain a little understanding.

 

[Bigrockk]

Received the parts today, kudos’s to Digikey, ordered yesterday from the US and parts were here today.
Put it all together and it seems to work fine. I only tested it as a single bank charger until I get it back in the boat but I highly suspect all is ok now.

I have a sneaky suspicion that the fan was bad from new, the first time I plugged it in there was a high pitched squeal for about 5 minutes and then it was silent. Now if I listen close I can hear the fan running even with the case closed up. The original fan was full of rust and corrosion but everything else inside was clean??

A big thank you to “Sunnysky” for the excellent help and the easy to understand explanations. Would love to buy you a beer someday!

 

[Bigrockk]

(Update ) I got the charger back in the boat and it seems to be charging bank 2&3 but not bank 1.
It may be a while before I get a chance to open it up again but I will take another shot at it.

 

[Bigrockk]

(Update2)
Well got it back home and this time I think I got it. The six little baby sugar cube relays energize in pairs for each battery bank. One of the relays for the battery bank one was not passing current. The coil would energize but I would get a 3 1/2 volt drop across the NO contacts. The 3 1/2 volts was the difference between actual battery voltage and charging voltage. I wasn't able to get the exact replacement locally but I was able to get one that was close enough so I went ahead and changed it. Bank one is charging ok now so I just have to get it back in the boat and see if it works when hooked up to all three batteries.
Just out of curiosity can anyone tell me what the Gold color component in the pictures is?


Relay Removed


New Relay in

An Overview

 

[Sunnysky]

GOld means 5%
Silver means /100

It is 0.29 Ω
http://www.michaels-electronics-lessons.com/index.html

 

[Sunnysky]

Received the parts today, kudos’s to Digikey, ordered yesterday from the US and parts

A big thank you to “Sunnysky” for the excellent help and the easy to understand explanations. Would love to buy you a beer someday!

Well if you are near Toronto...

 

[Bigrockk]

GOld means 5%
Silver means /100

It is 0.29 Ω
http://www.michaels-electronics-lessons.com/index.html

I believe we might be talking about different components. It is the rectangular component that looks to be wrapped in gold foil with a ground wire soldered to the side of it. It seems to me the gold foil might be some kind of shielding but I'm really not sure.

 

[Sunnysky]

ah yes
The gold foil must be for EMI shield for noise reduction on a magnetic part. Probably the switching torroid inductor.in a cube.

 

[Bigrockk]

Well good news, charger is back in the boat and seems to be working 100%.
@Sunnysky, thanks for the link, looks good!

 

[Sunnysky]

enjoy the boat