50-60's large battery charger. Things to check before power on? - Page 1
Forum section: electronics / beginners

author: dark_avenger
author_rank: Newbie
timestamp: May 02, 2014, 08:16:04 am
content: I recently got given an old battery charger that has spent the last 25+ years in storage, appears to be rated at ~60amps @ 12v.Not sure if it was in running order when placed into storage so just wondering things to check before I apply power and test.There is some corrosion on some of the copper leads and connectors so was going to clean/replace them. What else should I check?Thanks in advance,David

author: Rerouter
author_rank: Super Contributor
timestamp: May 02, 2014, 08:18:58 am
content: Its a transformer with good regulation and a geranium or selenium rectifier, test that the rectifier isn't shorted, and start it up with a variac if you have one, otherwise a 60W bulb in series, to act as a current limit,

author: Legit-Design
author_rank: Frequent Contributor
timestamp: May 02, 2014, 09:15:35 am
content: During catastrophic failure they produced significant quantities of malodorous and highly toxic fumes that let the repair technician know what the problem was.https://en.wikipedia.org/wiki/Selenium_rectifierI hope the dust has no chance of being toxic. Even if it was put to storage as working.

author: tszaboo
author_rank: Super Contributor
timestamp: May 02, 2014, 10:06:59 am
content: Using a lamp to limit the current. Nice, simple.

author: richard.cs
author_rank: Super Contributor
timestamp: May 02, 2014, 10:07:31 am
content: Quote from: Legit-Design on May 02, 2014, 09:15:35 amGiven the number of plates and the current rating I would expect this to be copper oxide rather than selenium but either is possible. I would power it up gently with a variac, without one I would do the lightbulb trick but I suspect you'd need something a bit bigger than 60W, the transformer may need a few amps of magnetising current.

author: dark_avenger
author_rank: Newbie
timestamp: May 03, 2014, 03:02:58 am
content: Thanks for the quick answers everyoneFriend has a variac so I'll take it around there to run it up. Should I just slowly turn the variac up from 0v or should I say start at 60v and power it up from there?Got a few closer up pics of the rectifier looks to be copper I think?10 plates in total.The two AC inputs into the rectifier (green leads) have about 5ohms between them which drops off to pretty much a dead short. Would this suggest the rectifier has failed?Model number and serial number tag if anybody was interested. Bit of googling has turned up nothing on this particular model just a little bit on others by the same brand.

author: David_AVD
author_rank: Super Contributor
timestamp: May 03, 2014, 03:11:07 am
content: Quote from: dark_avenger on May 03, 2014, 03:02:58 amIf the transformer secondary is still connected, you'll be measuring that and it will read almost a dead short at DC.

author: oldway
author_rank: Super Contributor
timestamp: May 03, 2014, 05:33:18 am
content: A transformer as old and subjected to moisture may have an insulation fault between primary and secondary.It may be a serious concern of safety.In all cases, there must be a grounding of case and output before any power on.

author: johansen
author_rank: Super Contributor
timestamp: May 03, 2014, 06:21:22 am
content: transformers don't magically die of old age and water intrusion.it takes time plus water plus heat to degrade paper insulation..your public utilites have these time constants figured out to a 1% error bound and they route power around hot transformers in real time.--chemical activity doubles every 10C or so..anyhow, no clue on that rectifier, i haven't seen anything that old.. err, not true, tube rectifiers count?anyhow, i would just power it up and if the rectifier blows up well, don't breath the smoke.a friend of mine got MS a couple years after building a DIY photocopier when he was 16, in the early 1960's --he probably got a good bit of selenium in his system.

author: richard.cs
author_rank: Super Contributor
timestamp: May 03, 2014, 07:39:20 am
content: Some advice before you power it up...For any mains powered device:Check (visually) for damage to the cable.Measure the resistance earth-chassis.Measure resistance between L&E and N&E, ideally with a high voltage insulation tester.For this specific equipment:Check the transformer is on the right tap for the supply voltage you intend to use it on.Wind the volts up slowly from zero (don't do this for switching supplies!)Connect direct to mains and gradually apply load.In case I'm wrong about the rectifiers being copper oxide; don't breathe any smoke if it goes bang.

author: oldway
author_rank: Super Contributor
timestamp: May 03, 2014, 08:30:54 am
content: These old transformers are not impregnated.The insulation is made of nomex carton and sometimes silk.The carton can rot due to moisture.Moreover, these old chargers do not have grounded secondary.To comply with safety rules,- Or secondary should be grounded and transformer should withstand 1500Vac between primary and secondary and between primary and frame. (Class 1)- Or the secondary is not grounded, the transformer must withstand 3000VAC between primary and secondary and between primary and frame. (double insulation class 2)I doubt that such an old rot transformer could meet the safety standards.Why risk his live with such an old charger which has no value at all.It's a piece of crap.

author: dark_avenger
author_rank: Newbie
timestamp: May 03, 2014, 09:25:42 am
content: Mains cable is OK, plug isn't the best but I'll change that before connecting it.The case is grounded but I'll make sure it's connected well.Tap is set for 240v already.I'll wind it up with the variac (On an RCD protected point) and if it lets out the magic smoke so be it but would be nice to do up as I think it's quite nice looking charger and having such a large amount of power available can be handy sometimes.Was more just a side project to get running and clean up to look alrightIf it's shorted in the transformer then that will be the end of it. If the rectifier is gone then I might see about replacing it with a silicon rectifier.Thanks everyone for the advice and assistance so far

author: Kjelt
author_rank: Super Contributor
timestamp: May 03, 2014, 09:48:24 am
content: Does it have a fuse of some sort? In any case make sure you have a fuse of 10 to 15 amps somewhere in your mains connection as fallback and have some spares just in case or a resettable one.

author: dark_avenger
author_rank: Newbie
timestamp: May 03, 2014, 11:18:06 am
content: Quote from: Kjelt on May 03, 2014, 09:48:24 amDoesn't have a fuse. I've got some fast blow 10amp fuses around here somewhere so I'll throw one of them inline.

author: Zero999
author_rank: Super Contributor
timestamp: May 03, 2014, 03:55:48 pm
content: Quote from: oldway on May 03, 2014, 08:30:54 amThat's all true. The insulation on old transformers can easily fail.If you're going to use it, at least earth the secondary but even then it still won't comply with the regulations.