OK, I see now. But you've got some apples mixed in with the oranges. Welders like the Mobi-Arc (are they still selling those?) "trick" the alternator into putting out something like 30 or 40 volts during welding. They do this by either fooling the alternator's voltage regulator to make it think it's generating less voltage then it really is, or by bypassing the regulator altogether and having a module in the welder act as the alternator's regulator. But it's the regulator that has the avalanche diode in it, not the diode rectifier pack. The avalanche diode is not recitfying the alternator's AC current. You need silicon power diodes for that. So you threw me off in your post when you said "the rectifier difference between the two alternator models." At any rate, the comment about avalanche diodes only applies to welders like the Mobi-Arc that need the alternator to output a much higher voltage then it was designed for. For Wes' use it is not relevant.
Hello all, will add some comments. Correct, we're no longer selling the MOBI-ARC unit....we developed a new line of products which have broader applications so although we still service and support MOBI devices, we're not placing new units in the field.
TrickT, your description of the way an alternator is used for welding is pretty accurate. In the case of the MOBI, the alternator's voltage regulator is either removed or incapacitated so it doesn't conflict with the regulator built into the MOBI control unit. So when welding in required, the MOBI regulator pulse-width modulates the alternator to create about 55 volts which makes it feasible to strike an arc. We don't de-regulate or fool the regulator into full-fielding the alternator, although that is the procedure home-grown,Premier/Link-arc/Thunderbolt....whatever it's called these days ....on-board welders use which is arguably dangerous as the voltage can get quite high when de-regulated.
The elevated voltage created during this process will conflict with the avalanche diodes which have become a common choice of diode/rectifier pressing to rectifier plates in many alternator. Avalanche diodes rectify the AC to DC and are used for a couple reasons: 1) they're slightly more efficient that standard high voltage silicon rectifier having a lower forward voltage drop, and 2) they start to avalanche or conduct at approximately 25 volts so if the regulation system were to go open circuit, the alternator's voltage won't go sky-high...it will be throttled to about 25 volts which is voltage level where the ECU and electronics won't be damaged. So from a high voltage electrical protection standpoint, avalanche diodes are good, but it's a deal-killer for welding as you need to achieve higher voltage to strike the arc so we would either not use those alternators that have avalanche diode rectifier plates, or swap them with rectifier plates we would spec with non-avalanche rectifier plates.
Thanks Tom for setting me straight! However I'm still a little cornfuzed: For the Mobi-Arc welder, whether it utilizes my OEM alternator or the HO from DC Power, it would use an external voltage regulator (Ford style; provided). I need to talk to Scott but I was fairly certain it was the rectifier, containing avalanche style diodes, that was the offending culprit (since the OEM regulator got replaced with an external regulator anyway...).
Please indulge me: For education/curiosity why do you think Toyota changed from non-avalanche style diodes to avalanche style diodes?
The alternator either had to be regulated by the connected MOBI, or if not connected, regulated by either and external regulator or sometimes internal regulator where we could disable the internal regulator when the MOBI was attached. The change to avalanche was due to slight efficiency benefit, along with a single point of high voltage protection.
I've pretty much got nothing more I can add, but if Scott or someone else can provide additional details I'm all ears. When I learned about semiconductors (many years ago now so things may have changed), avalanche and zener diodes were used in a way opposite to most diodes in that you reverse biased them and used the voltage that they "broke down" at to act as an accurate reference voltage in a regulator design. But the rectifier packs in alternators don't require a material property like that. They need to be able to pass a lot of current in the forward bias direction. So I just don't see why you'd use an avalanche diode in a rectifier pack if it wasn't part of the internal voltage regulator.
In this case the avalanche cause the diode to conduct at +/- 25 volts which then loads the alternator which then get hotter than s*** very quickly and then fails....all very dramatic.
No the Mobi-Arc welder can not be used with any Toyota alternator IIRCC. The early 100-Series model years (I believe through 2002 but maybe later), for instance, comply. But per Scott the Sequoia alternator definitely does not comply. This came up because I wanted, like the OP, to use the 150A Sequoia alternator but was advised not to...because of the avalanche style diode issue/incompatibility.
I'll see if I can reach out to Scott to have him comment here.
I can't remember which Denso alternator did or didn't use avalanche diodes...we used to check the BOM for a given alternator, drill down the rectifier plate, and description of the rectifier plate would detail if avalanche diodes were used, as it was common for GM after about 1985 to go that route, but Nippon-Denso, Hitachi, etc...used them on some alternators and not on others....it's kind of a pain which is why some providers of alternator-actuated welder require that they provide the alternator in order to insure the correct configuration of rectifier plate, regulator, etc... is used in order to achieve a positive installation.
