How to determine correct amps\voltage for rectifier diode. - Page 1
Forum section: electronics / beginners

author: koonamike
author_rank: Newbie
timestamp: February 24, 2023, 10:04:32 pm
content: I have an older schumacher se-2352 where the rectifier diodes have fallen apart. The original diodes have markings s1308 0548 IOR but I can not seem to find anything with that manufacturer. This model is a 200am engine start 35amp cast charge and 2 amp slow charge. Is there a rule of thumb on what voltage and amp ratings these two stud mounted diodes should be?

author: Benta
author_rank: Super Contributor
timestamp: February 24, 2023, 10:19:41 pm
content: Manufacturer is International Rectifier or IR.From size and charger specs, very likely 200 A rectifiers, if not more.

author: MrAl
author_rank: Super Contributor
timestamp: February 25, 2023, 04:12:36 pm
content: Quote from: koonamike on February 24, 2023, 10:04:32 pmHi,I've worked with stud diodes 20 times larger than that and stud diodes 5 times smaller than that and never saw one come apart like that unless something blew out.Maybe they were underrated to begin with.One thing though, if it was a 50 amp diode and you went with 100 amp that should be ok, and if they were 100 amp and you went with 200 amp that should be ok, and if they were 50 amp and you went with 200 amp that should be ok too, but they should be a similar size or an easy mod to a bigger size. What i would do is measure the package and then find a diode in the same size package as a reference for the current rating, then maybe go 1.5 times that or something for reliability.For the voltage rating you should probably go minimum 100 volts if they are on the secondary. I doubt they are on the primary.I would also SOLDER the wire to the top lead i would not use quick connectors like in the pic.Note you may have to drill out the holes a little if you go with a bigger size but you have to be careful about that.Also, the diodes may not come with any mounting hardware so you may have to buy that separately.Also, check to see if there is any insulator pad beneath the diodes. I dont think there is but if there is you need that too.It's also possible that only one has a pad.It's also possible that one (or both) are "R" versions that have anode and cathode leads reversed. You should check for that it's very important.I've worked with diodes that are as big and flat as hockey pucks, and diodes that have a body size about the size of an 8 ounce can of tomato paste and the bolt on the bottom being 1/2 inch diameter and the lead coming out the top (not a solder stud like those in the pics) was 8 gauge wire with a huge ring lug connector at the end for bolting to something else to make the electrical connection to the anode. They are pretty amazing devices.

author: bdunham7
author_rank: Super Contributor
timestamp: February 25, 2023, 05:23:58 pm
content: I can't find it again, but one stub of a reference I saw showed these as 80A 400V, which seems about right. You can probably use these:https://www.mouser.com/ProductDetail/Vishay-Semiconductors/VS-80PF80?qs=u%252Bh7cTrMUz%2Fba9z6K9iLYQ%3D%3DOr just look for other stud rectifiers that will fit with current ratings of 80A or more.

author: BillyO
author_rank: Super Contributor
timestamp: February 25, 2023, 08:04:59 pm
content: Some references..https://www.centurytool.net/SE_2352_Schumacher_Battery_Charger_Parts_List_s/30820.htm

author: Benta
author_rank: Super Contributor
timestamp: February 25, 2023, 08:11:09 pm
content: Quote from: MrAl on February 25, 2023, 04:12:36 pmNeither did I, but to me it looks more like corrosion than electrcal/heat failure.Water, salt water, perhaps even battery acid?

author: MrAl
author_rank: Super Contributor
timestamp: February 26, 2023, 11:49:03 am
content: Quote from: Benta on February 25, 2023, 08:11:09 pmYeah could be, very strange. Both of them too.

author: koonamike
author_rank: Newbie
timestamp: February 27, 2023, 04:24:59 pm
content: Quote from: MrAl on February 26, 2023, 11:49:03 amThis is an old charger that has had frequent and heavy use at my dad's mechanics shop. It wasn't ever left out in the rain though, and the area we live in has very low humidity so I don't think the diodes failed from moister. I think it was more related to age and frequency of use. I will purchase the 80 amp diodes as suggested and see if that works.

author: koonamike
author_rank: Newbie
timestamp: February 27, 2023, 06:32:59 pm
content: Quote from: BillyO on February 25, 2023, 08:04:59 pmI watched this video and it is he same charger as what I am working with. Probably less mileage on it though. On a side note, the video blogger made a questionable choice of a uniform for that video.

author: MrAl
author_rank: Super Contributor
timestamp: February 28, 2023, 12:48:33 am
content: Quote from: koonamike on February 27, 2023, 04:24:59 pmHi,Who said 80 amp diodes?

author: james_s
author_rank: Super Contributor
timestamp: February 28, 2023, 01:00:18 am
content: I'd probably just look on ebay for the biggest diodes I could find that would fit, it's probably not all that critical. Stud mount diodes can often be found cheaply on the used market.

author: koonamike
author_rank: Newbie
timestamp: February 28, 2023, 02:15:17 am
content: I was refereeing to the post by bdunham7.

author: koonamike
author_rank: Newbie
timestamp: March 08, 2023, 06:34:24 am
content: I bought some cheap 85 amp 600v diodes from ebay and they work as expected. Charger is back in service. Thanks for the advice @bdunham7 and all.

author: Vovk_Z
author_rank: Super Contributor
timestamp: March 08, 2023, 08:52:28 am
content: Quote from: Benta on February 24, 2023, 10:19:41 pmNo, I'm not sure. I've seen 200 Amp diodes and they are much larger or at least have both connectors very large and powerful (bolts or nuts). So, those on the picture are like 10-50 Amps rated. (Are they connected with a Faston 6.3 mm? Faston is very far from a tens amps).

author: bdunham7
author_rank: Super Contributor
timestamp: March 08, 2023, 03:20:51 pm
content: Quote from: koonamike on March 08, 2023, 06:34:24 amWere they physically the same size? Parts from eBay are scary--if they work, then great, but if they blow up at some point don't spend time wondering why. Undersized internals is one way of faking power rectifiers, voltage regulators, etc, and it is pretty common.

author: MrAl
author_rank: Super Contributor
timestamp: March 08, 2023, 04:48:29 pm
content: Quote from: koonamike on March 08, 2023, 06:34:24 amHi,Oh that's great it is always nice to hear that someone got their stuff up and running again.I myself dont buy anything from ebay anymore unless i absolutely have to. I have found too many sellers lie about the product specifications. That's not to say that they all do, but i can honestly say that about 90 percent of everything i bought from them was not as advertised, maybe more but i dont want to overshoot. That's why i avoid them and that means i have not bought anything from them in at least 3 years now, maybe more.The best place to get parts is from a parts dealer, and not a 'market place' dealer either. The best places have good return policies too.I hope your device continues to work well. If not, get your next part from a good parts dealer like Digikey, Mouser, etc.

author: james_s
author_rank: Super Contributor
timestamp: March 08, 2023, 06:29:50 pm
content: I've bought lots of parts from ebay that were fine, you just have to know what you're buying. Stuff like old used diodes and SCRs aren't going to be fake. The fake parts are most often vintage/hard to find or otherwise exotic parts.