Great DIY thank you so much for sharing this. I am going to use you Zn plating recipe
seems like a good one from the look of your parts and low toxicity. I also like the configuration of your anodes seems like a good simple way to get even deposition. Could you if you don't mind please provide your recipe for the Ni plating bath? And a couple of questions Do you pickle the parts in muriatic first? any other prep tips? And a picture of how you wired the variac. Very good of you to take the time to do this tutorial.
When I was an undergrad the chemistry club president(me) made stoichiometric Hydrogen and Oxygen balloons for a career fair demo, the first one I lit off knocked 50years of dust off the ceiling tile in the auditorium. Most people left in a big hurry....They added some new rules to the chemistry demonstration handbook on that one. The President of the University was SERIOUSLY MAD, I thought he was going to have the big one right there. We beat a hasty retreat. Cant hurt to run a fan in the room just in case
I have a somewhat similar story that ended in new rules relating to demos for grade school kids. Something about sodium metal and water and a big pop.... It's all a little fuzzy now. [emoji6]
I had not been pickling my parts for the zinc stuff. You can. We did do it for the nickel parts. Most of the time after sandblasting I don't typically feel it's necessary. It won't hurt anything though and if you have some stubborn rust pits it will help clean them up.
On power supplies, here's a couple bits of advice. I think I quoted a current density above. If you are doing small parts, you can use a wall wort supply for power. Some of them are good for a couple amps. If your variac is a real old school variac, you can use it to regulate a battery charger. Wire the output of the battery charger into the input of the variac and the output to you parts. I used an outlet for the connection point so as not to have to cut off the standard wall plug. This method works but it's pretty taxing on the battery charger so I wouldn't use a charger you care about and the dumber it is the better. Smart chargers may think they are shorted or the battery is charged and shut off.
The problem if you are going to do large parts is you need a lot of current but you want very low voltage. There are ways to design the system to minimize the voltage. More anode surface area is good. It cuts down on the resistance so it takes less voltage to push the current. The battery charger will get you around 6-8 amps if you attenuate the voltage. That really will do most things.
The third option if you happen to have a really large transformer around.., say s 5kVA like this:
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Because everyone has one right?? WARNING!!!!! We are now dealing with serious current. It can be dangerous. If you don't know what you are doing.. Don't do this.
So a high current and low voltage power supply is hard to come by or expensive. There are other routes to it but I'm not an electrical expert so I'm not going to do a huge tutorial but some reading on repurposing microwave oven transformers.
It's a lot easier to regulate the AC side than the DC side. It's much lower current. In this case I'm feeding that giant step down transformer with a variac. It steps the 120 down to 30v max. By varying the input voltage, the output is also varied. But it's still AC. Need to convert it to DC. To do that you need a rectifier. Search bridge rectifier if you want to know how to build one or how it works. I picked up a single phase 100 amp rectifier with heat sink from Amazon (it's the black box with the wires hooked to it). It gets hot and needs to be cooled. Yes rectified DC is "dirty" but you aren't running a computer here. I highly recommend an ammeter and a volt meter to watch what's going on. At these currents you probably will need a shunt for the ammeter. HF jumper cables are a good source of big wire and clamps. Remember you have to size things appropriately. It's going to get hot if you are pushing a bunch of current through the system. The bath will get warm too.
Hopefully that answered a few questions.