A Batch #2 Update of Sorts, Featuring A Warning About Solid State Power Relays and the Joys of Quality Control
As I am sure you guys know, Flux Deluxe Batch #2 has been taking me a while to build out. I have only shipped one (1) heater from batch #2 to date, though more are in progress and close to being done.
The chief reason for this delay is the 25 hours of shop time I've spent in the last week working on a very nasty hardware issue.
25 hours of shop time is most of my weekly allotment, so I have been doing a hell of a lot more troubleshooting than building of late. Those hours finally bore fruit last night, however, and I have a smoking gun sort of identification for my power relay issue.
I now have a cause, and I believe I also have a solution.
The issue: As I mentioned in a few recent posts, I have found that a number of power relays from the last batch I purchased are either DOA or came to me partially failed, with one critical foot already in the grave. I've counted at least 14 bad relays out of the last 20 I've installed.
The first six of those failed consecutively, and let me tell you, that sort of thing is hell to diagnose and REALLY messes with your head.
The blue, rectangular PCB below is the power relay in question:
I will explain the two types of failures I have observed with this relay so far, the steps I have taken to address this situation on my end, and what we can do if your power relay has failed or fails in the future.
But first, what is a relay and what does it do?
Relays are switches that open and close circuits electromechanically or, as in this case, electronically. Relays control one electrical circuit by opening and closing contacts in another circuit. In the Deluxe, the tactile switch is connected to the power relay, so pressing (closing) the tactile switch also closes the relay, allowing high current to flow to the heater. This relay is integral to the design of the Deluxe. It's functionality is more complex than a simple on/off switch.
Types of Power Relay Failures I have Observed:
I have observed two types of power relay failures,
Full Failure and
Partial Failure. Both failures are fixed by replacing the power relay's MOSFETs, and as far as I know the
only way to fix these issues is by MOSFET replacement. Consequently,
if your power relay fails you'll need to send the heater back to me for the repair.
Full Failure: This type of failure is obvious - the unit does not work. The "in use" LEDs may or may not light up as if it should be working, but the power relay won't actually send any power to your heater. Basically,
"It's dead, Jim."
Partial Failure: This type of failure MAY NOT be obvious if you aren't paying attention, and it's also potentially dangerous: the unit heats up, but it does so from the flip of the power switch, not the press of the tactile switch! This occurs when one or both MOSFETs in the power relay fail internally, and allow an internal path to ground where none should exist. This has the effect of bypassing the tactile switch and allowing the heater to unintentionally power up, which it will do until it is stopped by the thermal fuse. Yay, thermal fuse!
Those are the two types of failures I have seen so far on my workbench. There could be more, and if I become aware of more I will share them with you.
How to test your Flux Deluxe for a partial MOSFET failure:
Here is a test you can easily do yourself to see if your unit has a partially failed power relay MOSFET. I am hopeful none of you are affected, but if you are, the repair is very a straightforward chip replacement.
How to test for a partial failure of the power relay:
- Make sure the unit is powered off and the coil is cool to the touch.
- Rest the Dynavap in the coil with the vapcap installed. Do not depress the tactile switch.
- Toggle the On/Off switch to On, but do not depress the tactile switch. Wait 10 seconds or so.
- If your vapcap heats up (and clicks!) without pressing the tactile switch, your power relay has partially failed, and you'll need to send your heater to me for repair; I'm sorry. Please send me a PM if this happens, and we will discuss the next steps.
- If nothing happens and it just sits there, it's fine.
What I am doing to address this situation:
As I said above, this relay is integral to the design of the Deluxe.
Since I depend on it, I need to make it work. To achieve that,
I plan on making it stronger by proactively installing better MOSFETs. Going forward, I'm adding a step to the build to replace the questionable factory-installed MOSFETs on the relay PCBs with new, high quality ones I source from a known good source such as Digikey (e.g., these:
https://www.digikey.com/products/en?keywords=785-1221-1-ND). This swap will add a few minutes of build time and about $1 to the cost of each heater, but that will be time and money very well spent (!) if it resolves this issue. I am hopeful that better quality MOSFETs will solve this issue going forward, but I acknowledge we won't really know until we use them and see how they behave. These same relays are widely used in other IH installs, so I believe these are "just" a bad batch of components, but I'll keep my eyes open as I do more research, and will report back if it proves to be otherwise.
I have not seen either of these failures appear in the wild yet - and of course, I hope that continues - but I want to get the info out there so you know what to look for in case your Deluxe starts to act strangely!
That's what I know now.
Thanks!
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External Power Supply Update: Oops, I need to walk this one back!
And in more good news, I need to walk back
the tip I shared a few days ago about using the Deluxe with an external power supply.
Please do not use the Deluxe with an external power supply at this time!
The thermal fuse for the Flux Deluxe is wired in series with the B+ battery lead. If you use an external power supply, you bypass the battery completely, and thus also bypass the protection of the thermal fuse. That's not good and NOT recommended!!!
I missed this safety gap at the time I made my previous post, but I see it now and want to bring it to everyone's attention.
Sorry to tease you all, but I'll work on making this a more formal feature in the future.
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Sigh...I think that's all the news of this sort I have at the moment.
Happy Thursday afternoon, everyone.