3 ms·

The really scary thing is that as he points out, it actually seems to be designed with an apparently reasonable amount of isolation between the primary and seco

by makomk 11y ago

The really scary thing is that as he points out, it actually seems to be designed with an apparently reasonable amount of isolation between the primary and secondary - it's just that something managed to completely abrade the insulation. Not sure if it was UL compliant as designed because their requirements for transformer construction are quite complicated, but it certainly seems plausible. He's reviewed numerous really questionable power supplies[1] with a gnat's whisker of separation between the mains and low voltage sides and much more dubious transformers, but somehow none of those actually managed to put 240 volts on the output... [1] Such as the cheap shitty pink USB charger from China: https://www.youtube.com/watch?v=ioAq7PI1Uwg https://www.youtube.com/watch?v=ioAq7PI1Uwg

Animats 11y ago
The really scary thing is that as he points out, it actually seems to be designed with an apparently reasonable amount of isolation between the primary and secondary - it's just that something managed to completely abrade the insulation. That's the argument for a split bobbin. With a hard plastic wall between the two coils, in addition to the wire insulation, it's hard to get a short between both side of the transformer. Here are some split-bobbin transformers for switching power supplies on Alibaba.[1] Split-bobbin seems to add about $0.10 to the price, raising it from $0.89 to $0.99. [1] http://wholesaler.alibaba.com/product-detail/EE22-split-bobbin-transformer-for-charger_60428582199.html http://wholesaler.alibaba.com/product-detail/EE22-split-bobb...
- PhantomGremlin 11y ago
  Split-bobbin seems to add about $0.10 to the price, raising it from $0.89 to $0.99. So, there it is. Good luck finding a miscreant to hold accountable if this sort of cost reduction kills someone. And even if you could hold the culprit accountable, that still can't undo the loss of life anyway. It's all just collateral damage from the race to the bottom.
- userbinator 11y ago
  Price aside, split bobbin construction also leads to lower efficiency since there is less effective coupling between the two sides. It's always about tradeoffs, sort of like how you can ride a motorcycle or drive an armoured vehicle. What is safer won't necessarily be better in the other dimensions.

by makomk 11y ago

Animats 11y ago

The really scary thing is that as he points out, it actually seems to be designed with an apparently reasonable amount of isolation between the primary and secondary - it's just that something managed to completely abrade the insulation. That's the argument for a split bobbin. With a hard plastic wall between the two coils, in addition to the wire insulation, it's hard to get a short between both side of the transformer. Here are some split-bobbin transformers for switching power supplies on Alibaba.[1] Split-bobbin seems to add about $0.10 to the price, raising it from $0.89 to $0.99. [1] http://wholesaler.alibaba.com/product-detail/EE22-split-bobbin-transformer-for-charger_60428582199.html http://wholesaler.alibaba.com/product-detail/EE22-split-bobb...

PhantomGremlin 11y ago
Split-bobbin seems to add about $0.10 to the price, raising it from $0.89 to $0.99. So, there it is. Good luck finding a miscreant to hold accountable if this sort of cost reduction kills someone. And even if you could hold the culprit accountable, that still can't undo the loss of life anyway. It's all just collateral damage from the race to the bottom.
userbinator 11y ago
Price aside, split bobbin construction also leads to lower efficiency since there is less effective coupling between the two sides. It's always about tradeoffs, sort of like how you can ride a motorcycle or drive an armoured vehicle. What is safer won't necessarily be better in the other dimensions.