Please help me fix my battery charger. - Page 1
Forum section: electronics / repair

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: May 10, 2019, 07:45:40 pm
content: Hi, my old batter charger stopped working and I would like some help in diagnosis and repair.As you can see from the attached photos it's pretty old and alas I cannot find any schematics for it. I replaced all the diodes in the heat sink since the metal leads were coming off on their own as a result of metal fatigue. I checked all the switches etc. It still is not outputting any voltage.Pretty sure it works like this: AC comes in and is transformed to several different voltages through the multiple taps in the transformer. It can be selected to charge 1 to 8 batteries by the use of the push button switches on the front panel. It then goes to the diodes for rectification and then out to the plus and minus terminals which connects to the battery. It looks very simple but it has me stumped as to why its not functioning.If anyone has any suggestions or know where a schematic can be found you help would be greatly appreciated.

author: wictor
author_rank: Regular Contributor
timestamp: May 11, 2019, 05:49:03 am
content: Hi,Do you have a multimeter? I don't think you need schematics, since this should be so simple and I believe that you already described how it works.But if you have a multimeter, start by measuring that you have ac voltage coming in. Then measure input voltage to diode bridge and output voltage also with different front panel switch positions. And let us know the results, so we can help.I don't see the other wire in the front panel (current?) meter. Is it bypassed by connecting both wires to same terminal? It seems that red output wire is either broken from other terminal or then it is wired to somewhere else. The picure is a bit dark, so I cannot be sure.Wictor

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: May 11, 2019, 12:35:04 pm
content: The front panel amp meter is not working and needs to be replaced. I checked in coming voltages and it's getting mains (120) volts to the transformer. The switch works as I checked it with a multimeter. I'm not sure its wired up correctly. The diode rectification seems a bit weird to me as there are 4 diodes. Two seem to be wired in parallel and the other two go to different taps of the transformer. The two black wires on the top of the two diode packs are the positive and negative to the battery wires for the battery.I will post more photos.

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: May 11, 2019, 12:36:51 pm
content: Here is another photo of the diode packs.

author: wictor
author_rank: Regular Contributor
timestamp: May 11, 2019, 02:04:04 pm
content: Quote from: joseph nicholas on May 11, 2019, 12:35:04 pm4 diodes = standard full wave rectifier. Seehttps://www.electronics-tutorials.ws/diode/diode_6.html

author: wictor
author_rank: Regular Contributor
timestamp: May 11, 2019, 02:33:01 pm
content: Quote from: joseph nicholas on May 11, 2019, 12:35:04 pmIn the first post you said that charger stopped working. Have you modified the wiring or why do you think it's wrong?And when you replaced diodes, were old diodes all the same type and did you replace with same or equivalent?Wictor

author: tautech
author_rank: Super Contributor
timestamp: May 12, 2019, 08:23:16 am
content: I'd guess you have the wrong case style diodes installed.Did you check they were the same polarity as the old ones ?There may have even been both types, cathode case and anode case.Better solutions are available than when these old chargers were made an I urge you to use a single bridge for simplicity.Something like these will work just fine:https://nz.element14.com/solid-state/kbpc5010/bridge-rectif-1ph-50a-1kv-kbpc/dp/2101168?st=diode%20bridgeBe sure to use some heatsinking compound and try to incorporate the heat sinks you have already to be sure to keep the bridge cool.

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: May 12, 2019, 11:27:08 am
content: The diodes were replaced with new ones with the same polarity. Same serial numbers. The polarity is the same. It'm starting to think the transformer may be defective. I was hoping someone on the form was familiar with this brand GB Gray and had some repair experience with this monster.

author: wictor
author_rank: Regular Contributor
timestamp: May 12, 2019, 11:31:05 am
content: So you have two wires coming to diodes(AC) and two leaving(+ & -). Do you have any voltage on those terminals?

author: tppc
author_rank: Regular Contributor
timestamp: May 12, 2019, 11:47:02 am
content: I am sorry to say that, but how do you want people here to help you if we see nothing on your pictures?Actually, we can not follow the wiring on your pictures.You may consider drawing the schematic from what you see inside your charger and then post your hand drawn schematic.Regards.