Geoff Weeks

You need both positive and negative for full wave rectification. If it is being used on a positive ground vehicle the positive rectifier can be mounted to grounded metal, but the negative would have to be isolated from any grounded metal.

It will probably cost you the same or more to rig up some replacement rectifiers out of new diode blocks than it would to buy a used or re built modern one wire unit. Because yours is positive ground, you either need a case neutral (Like the Leece Neviile JB series) or a positive ground unit.

https://www.aspwholesale.com/index.php?route=product/product&path=71_262_274&product_id=6244 https://www.aspwholesale.com/index.php?route=product/product&path=71_262_274&product_id=6243 There are other choices and other vendors, I just pulled these off the net. this set is used in 130 amp Leece Neville alternators. Because of how the mount in the case in the alternator they were designed for, there is very little heat transfer to the case, so that makes them more ideal for a retro-fit where they will not be bolted to an aluminum case and have a lot of cooling are drawn over them. It is a good bet that your rectifier has failed, but as Paul says, before you pull the trigger on more than $100, test them.

Paul while I agree with you about lock ring wheel (I still use them, both on my antiques and up until I retired, on my linehaul stuff). I think the selenium rectifiers have plenty of drawback besides the toxic failure mode. They have a short lifespan compared to modern stuff, and for the most part any you find today are going to be at least 60 years old. At 12 volts you are running close to the limit for what one plate can safely handle in terms of PIV. As i mentioned before diode blocks out of a JB 2600 or JB 2800 would be fine. The spec's have already been taken care of for you as has the heat sink. The Leece Neville JB series today starts out at around 100 amps and goes well over 200. Initially they were made as low as 60 amps, but I haven't seen on of those in decades. I've included a photo of the Selenium rectifier and the JB blocks so you can get an idea of size. They would fit the bill, are nowhere near their limits (same blocks used on 24 volt and higher alternators) The black "kidney" shaped objects are the diode blocks.

Some more Wiki quotes: Hydrogen selenide is an inorganic compound with the formula H2Se. This hydrogen chalcogenide is the simplest and most commonly encountered hydride of selenium. H2Se is a colorless, flammable gas under standard conditions. It is the most toxic selenium compound[3] with an exposure limit of 0.05 ppm over an 8-hour period.[4][5] Even at extremely low concentrations, this compound has a very irritating smell resembling that of decayed horseradish or 'leaking gas', but smells of rotten eggs at higher concentrations And: Exposure at high concentrations, even for less than a minute, causes the gas to attack the eyes and mucous membranes; this causes cold-like symptoms for at least a few days afterwards. I There are better rectifiers available. "Smells like rotten eggs in higher concentrations"

Pictures? Important to know WHY it happened, was the spring break a result of the collision or the cause?

It is up to you and the look you want, but here is my take (from an old flatbedder/heavy haul) cabinet style lockers are a pain for chain storage. Cheap but effective is to weld a heavy piece of flat stock along the top of the cab protector, with some added stiffners/ supports on the run, then hook the grab hooks from the chain on and interspace a binder in between. from the hook to the floor back up to the binder lower hook, back down and then back up to the flatstock. That way the chains don't get tangled and there is a binder with every chain. If the top of the cab protecter/bulkhead is 5' a 16' binder chain will not reach the floor and a 20' will barely. You can add a "chain tray" near the bottom if that is your preference.

If it come down to a failed rectifier, and it is looking that way, I would caution against looking for a replacement of the same type. I haven't checked mine, it may still be good, or it may not, but there is no way I am going to put it back in service. These selenium rectifiers were well known in small power generators of old (Onan and the like) for supplying field current. They are known to fail and are replaced when ever they are found, even if they haven't yet failed. With selenium, it is not if but when. Unlike silicon diodes which rarely fail in the life span of an alternator, selenium's are known to have a much shorter lifespan and heat tolerance. It was why the quickly disappeared when better diodes were invented. With silicon diodes an alternator is likely to not see a failure in the lifespan of the unit. Bushes,slip rings and bearings are now the much more common fail points. Brushes are cheap and easy to change, but when you get into slip rings and bearings it is often cheaper to replace than repair, unless there is a over riding reason to do so. When I overhaul an alternator, if the slip rings are shot, I generally don't bother replacing, I use it for parts. It didn't take me long to switch to brushless units for my stuff, as they can take higher duty cycles than brush units. Even pushing them to max output for hours at a stretch, the only time I had a diode failure was when something internally shorted the output. There are now air cooled alternators that exceed 300 amps, a domain that used to be exclusive to oil cooled units like the Delco DN-50. 100 amps is small by today's standards, and there are plenty of pre made diode blocks (diodes already pressed into a heat sink) that would make a fine replacement for the selenium unit, last longer and take less space and don't off gas toxic vapor when the fail.

Looking more and more like a failed rectifier, but TEST don't guess. READ THE ABOVE!!! HIGHLY TOXIC!!!

Selenium rectifiers had a shorter lifespan than desired. In the early stage of failure they produce a modest amount of sweet-smelling gas. Sometimes described as 'sickly-sweet'. At that point the rectification properties are almost totally gone, allowing reverse voltage to leak through the rectifier. During catastrophic failure they produced significant quantities of malodorous and highly toxic hydrogen selenide[8][9][10] that let the repair technician know what the problem was. By far the most common failure mode was a progressive increase in forward resistance, increasing forward voltage drop and reducing the rectifier's efficiency. During the 1960s they began to be superseded by silicon rectifiers, which exhibited lower forward voltage drop, lower cost, and higher reliability.[11] k Quote from Wiki, Also have heard and read it elsewhere. It is the prime reason, that I planned to replace mine with silicon diodes, which as you say will not smell or emit toxic fumes when they fail.

Yep, when the fail, and the stuff is toxic so don't go sniffing. Run the test and I bet you'll find a bad rectifier, but test to be sure.

I'd just grab some diode blocks out of a Leece Neville JB2600 or JB 2800 and then the hard part, you need to assure airflow over them and they must be isolated from any other metal, and protected from wrenches etc. None of the silicon diodes used in modern alternators have anywhere near the surface area on the heat sink that the one you are replacing. Granted they can take the heat a little better.

You could but I wouldn't. PIV (peak inverse voltage rating) should be 2.7 x the max forward voltage for a minimum, Most will go a fair bit higher when selecting a diode. Why not use a 1600 volt rated? Because the higher the voltage rating the more the voltage drop across the diode, so where a 100v PIV may have .5- or 1 volt drop across in the forward direction, a 1600 volt would be much high drop. Although as a percent of rated voltage the drop may remain the same, at lower voltages the forward drop may present a problem.

Has it tested bad?

Paul, electrically you are correct, but in this case the "grounded" side of the field is wired to the DC output of rectifier. A heavy ground wire carries both the output and the field ground path. I think the reason for this,is these are (were) sold as an upgrade to what the chassie mfg had. Mine is wired (and looks to have a complete original wiring) to the DC output on the rectifier also. This allows Leece Neville to pre-wire the kit, and which ever side of the rectifier you ground (positive for positive ground, negative for negative ground) the system will work with the same supplied voltage reg. No need for positive and negative regulators and no re-wiring by the end user. It was a trait of Leece Neville's that carries on to this day. While Delco and many others produce separate positive and negative ground units, Leece Neville made theirs neutral, and you ground the output terminal for the vehicle polarity it is being installed on. It means, unlike Delco's and others you can't use the case directly for a heat sink on the "ground" side. Both in the old selenium rectifier and on modern diode "bricks or blocks" are isolated from the surrounding metal, and in the case of the old selenium rectifier, they put a whopping big relay in the output so the battery and rest of the trucks electrical system is isolated from the rectifier when the engine is off. Makes for a simple "kit" but looks a bit odd.

I call a test light my "optical volt meter".

Interesting, I had not run across that before. Motor coaches sometimes had "buttons" on the floor exactly like high beam/ low beam switch but one for left turn on for right.

Love that drawing, never seen it before. I was very careful to say ground and not negative, because it doesn't matter to the vehicle which polarity but some items may care. The basic operation is the same regardless of which battery terminal is connected to the frame, or if none are and everything uses two wires (like in marine). It is very possible that the rectifier is bad, but it wasn't the 1st place I'd leap without other indications. This system is a bit odd, as it disconnects the battery from the outlet (DC side) of the rectifier when the ign is switched off. Electrical can be hard to explain over the internet to someone who is not well versed in how the system works. Often easier to show then tell. Even harder (for me anyway) to learn solely from a lecture or text (likely why I didn't do well in school) then having my hands in and someone showing me how and why.

modern replacement for the rectifier: https://bermantec.com/shop/products/alternators-spare-parts/prestolite-leece-neville-alternators-spare-parts/leece-neville-rectifier-regulator-1111ca/ Add shipping and import duties (couldn't find one listed in the US) all comes to much more than a one wire modern 100 amp replacement. Here is another but shown "sold out" https://hdpsi.com/collections/33hd-series-external-rectifier-models https://hdpsi.com/pages/external-rectifiers

Ok, this suggests it is not the voltage regulator if changing it did no good. On to testing the rectifier as if shorted it could put a high ac spike into the system giving a high reading. Meter reads the ac. Normally you would drain the battery (with a shorted diode) with the engine off, but the main relay in the reg prevents this as it disconnects the battery from the rectifier when the ign is off. Turn the ign on (should hear a click in the regulator) then take a test light, one end on a good ground, and probe each of the heavy ac output wires from the alternator (NOT the heavy DC wire to the reg) and if the light lights, the rectifier is shorted. Resistor resist current flow, there job is not to reduce voltage, voltage drops when you try and pass a current through the resistor but how much varies with the current (load) Also were are talking massive wattage so any resistor would be huge and the energy wasted would be in the form of heat.

this seams to imply that it was 18 volts before and after the regulator was replaced. Is that so? That would point to other problems Are you sure of your volt meter?

This is how I understand it: It was working fine, then it went to 18 volts, then the regulator was changed, then it stayed at 18 volts. If this is not the sequence than let me know what is. Two regulators being bad, is not as likely as one. There are resistor cards under the base of the regulator that cut the field current in stages. If one of these has failed it can not do its job. So there may be other reasons the regulators can't keep the alternator under control. Wiring and grounds are chief among them here. If it was working, then went to 18 volts, and the regulator was changed, and it went back to working for a while, then went back to 18 volts, then there are other suspects. The regulator works much like a single pole double throw relay. The top contact provides full battery voltage to the field. the field is connected to the movable contact. When the contact is neither touching the bottom or top contact, the field is fed power through the resistor cards, at a center tap. when the relay pulls all the way in and the moveable contact is touching the lower contact, the field is shorted to ground (no field current). In practice, the center contact is always dancing between the three positions, sometime touching the top sometime the bottom and most of the time in the middle, all based on the voltage supplied to the relay core. If one or more of the resistor cards are burnt too much current get to the field. If the regulator isn't well grounded, it may see only 11 volts between it and what it is attached too, even if the battery is seeing 16 volts, the regulator thinks it needs to raise the voltage when it really need to cut the voltage. This is what I mean by poor ground. The battery is often grounded to the frame, but the engine and body are often mounted in rubber bushings, so if you don't have good ground bonds, the voltage the body sees may be different than the voltage the engine sees, which may be different that what the frame sees. Good ground bonds are essential. If the field current is too high, because of a short in the field, or a 6 volt field being used as a replacement sometime in the past, because it looked right and fit, it could be burning the resister cards in the regulator, A check of the field current might give some answers, but I don't have the spec's. There are an awful lot of unknowns at this point. If you are working by yourself and aren't well versed in how to check these things, (often times it is much easier to show you than tell you how to run the checks) I would seriously have you consider a modern alternator set-up. There is also the rectifier situation, If you read the Wiki link I posted you will see that type of rectifier suffered from shorter life span and releases toxic fumes when it fails. I would hang onto the old set-up for show, but would suggest going with a modern unit for operation. When I get time, I am going to look into making a rectifier mount that will accept modern Leece Naville diode blocks, to mount on the rear of the alternator case, such that the cooling fan in the front of the alternator draws air over the diodes before it enters the rear of the alternator. The mount not only must hold the rectifiers blocks but also be electrically insulated from the alternator case, as well as being sturdy enough to take the vibration and heat in use. It must also protect from falling wrenches and such during maintenance. In modern alternators they are mounted inside the rear cover with insulating washers and feed throughs on the rear case. There isn't room for them inside the alternator case, I checked.

Replacing the rectifier is going to be a problem. There are remote rectifiers with a fan, as an assembly, but you are looking at several hundred dollars, and will not look like original. I think it is time to make the choice, original or retrofit? Nothing wrong with the original alternator, but the rectifiers are not the best, it was all that was available at that time. A replacement modern alternator, can equal or exceed what you have now, and all in the same footprint. I think I would either leave it be, or replace with a modern unit. Like I said, I have the same set up, only difference is your field is 12 volt and mine is 6 volts. If you go with a modern unit, it would eliminate the divorced regulator, the new ones are all self contained. So in short leave it as it is now, I wouldn't open it up unless you detect a bearing problem. The brushes and brush holder can break easily when you try to remove. Last I checked, they were still to be had, I have one stuck/broke one in my alternator and purchased are replacement brush holder. My brushes looked ok so am not going to replace. The other option, is to replace. Your choice.

Here is a simple test you can do. Get a test light, connect one end to a good ground, turn on the ign switch and touch the other end of the test light to each field terminal. It should light on one and not on the other. If it lights on both, you have a bad ground, if the doesn't light on both, either you have a bad regulator or it is set -up different than mine and regulates the ground side of the field (not likely, but can't rule it out.) Anything more and we are going to have to get deep into testing stuff that is hard to explain over the .net.

The two small wires on the back are field wires. One should go back to the field terminal on the regulator. Because your regulator is not identical to mine, I can't be sure where on the rectifier you connected the other will make a big difference. If i had to guess, I would guess the one field wire not connected to the regulator would go to ground, but without seeing the regulator and tracing out how it works, I can't be sure. The simplest course of action would be to replace with a modern "one wire" alternator, and do away with the troublesome rectifier and divorced regulator. It depends if you want period correct or not. You need someone who understands the system to guide you. This kind of work is very hard to diagnosis over the internet