Replacing the Selenium Rectifiers in Century 30A/200A Portable Chargers

Fifty or Sixty years ago, Century Manufacturing was busy building heavy duty portable chargers that were elegant in their simplicity and brutally effective. The most common version was rated 30 amp continuous output and capable of 200 amp boost. They are known by various model numbers:

• 141-037
• 141-108
• 141-118
• 141-131
• 141-290
• 141-243
• TY5104
• 1100
• 3Z631
• 407391R91
• 407391R92
• 87152
• 87150

.. and probably many more. They were sold with appealing brand names like Century, Solar, Sears, Dayton, John Deere and others. But inside, they were unpretentious and built with minimal points of failure that virtually guaranteed longevity.

The user interface consisted of a power selection switch and an amp meter - if you desired anything fancier you needed to just move along and keep looking. These chargers had very heavy, rugged transformers that force-fed batteries with unapologetic efficiency. What they did not have was a lot of namby-pamby bits and pieces that have long been considered necessary and thus standard - then as well as now. There was no timer, no cooling fan, no DC circuit breaker, and certainly no "automatic" anything. This charger didn't care a whit about hurting your battery's feelings.  If YOU cared, then you needed to be prepared to turn it off when the battery started whining. In short, they were glorious.

These chargers were designed back when selenium rectifiers were a thing, which they no longer are. Selenium rectifiers are now routinely replaced with silicon diode units, for a lot of reasons - just accept it. The issue with these old workhorse chargers is that for reasons known only to the good engineers at Century, they decided to install two selenium rectifier plates and place them on opposite sides of the charger, riveted to the cabinet side panels. Then they connected them to the charger's other necessaries with wires running back and forth that more closely resembled a booby-trap than sober engineering.  And we all know that the rectifier is the single most commonly damaged component in the charger - so, thanks a lot to the engineering guys... pffftt.

So it's now half a century later, and the world is full of these great old chargers, but they just don't have the output they should have and they need their old rectifiers replaced. But even if we wanted to put selenium rectifiers back in these things, they are no longer available. We all want to resurrect them, but the logistics of replacing this over-wrought rectifier arrangement has vexed charger-whisperers ever since we opened our first one and it literally laughed at us. It's not that it can't be done. It's not even difficult. But it is hard to explain with mere words. 

Before we go any further, here's the parts list for this job:

696605 - 100A Compact Rectifier - Negative Base

696624 - 100A Auto-Reset Circuit Breaker Kit

You will also probably need some miscellaneous electrical supplies and a crimp or solder lug for the DC output cable - 6AWG with a 1/4" lug hole.

So, in the spirit of a picture being worth many many mere words, let's get to the pictures and show how you too can replace the old selenium rectifier in your crippled charger and bring it into the modern era...

It's worth noting here that like most Century chargers, this unit is "Negative Output", which simply means that the output from the rectifier plate is connected to the negative DC cable.

A big shout-out to Scott P. at PLP Battery Supply for supplying the pictures used here.