Inverter Generator Repair

[PM5K]

I have an inverter generator that has two bad caps. One blew and the other was swollen.

My main issue is that the power supply
is encased in some type of epoxy.

My main concerns are regarding the epoxy and its purpose. I can imagine that it helps with vibration should I also be concerned with sparks since it’s a gasoline generator?

The plan is to break off the old caps, cut the old legs off, clear out the solder points, then solder from the top since I cant get to the backside of the board.

This means that the legs of the caps will be exposed, where as before the entire cap sat maybe a quarter of an inch in the epoxy. I’ll have to at the very least bend the legs of the caps and find a way to adhere the caps to something so they dont vibrate.

So those are the concerns/questions.

Can I leave the legs exposed?
What can I use as a “glue” for vibration?

I have already done the repair as a temp repair and the generator now works.

Lastly, I’ve heard a good way to make caps more resilient is to up the voltage but keep the same capacitance, seeing this is an inverter, can I do that and does that actually make sense? For the record there are two 35v 1000uf caps that failed.

TIA!

[PM5K]

Here is an image for anybody that needs to visualize it.

I am also starting to think jumper wires are better than bending the legs of the capacitor?

https://www.badcaps.net/forum/attach...1&d=1673672501

[stj]

that crap is usually to keep moisture out.
is it really epoxy? often it's polyurothane and is pretty soft and flexable - specially if you heat it first

[momaka]

Originally Posted by stj

that crap is usually to keep moisture out.

^ This.

Basically when you move the generator from a cold to a warm place (or vice versa), you may get condensation to start forming on the parts... and that can lead to problems with the electronics parts.

Originally Posted by PM5K

My main concerns are regarding the epoxy and its purpose. I can imagine that it helps with vibration should I also be concerned with sparks since it’s a gasoline generator?

Sparks - no.
But moisture/condensation - yes.

Originally Posted by PM5K

Can I leave the legs exposed?

Yes, you don't have to coat the boards in glue or anything else. However, if you leave these exposed, then you have to be careful when bringing in the generator from cold storage into a warm room temperature or the reverse to prevent moisture formation on the circuit boards and other parts.

Originally Posted by PM5K

What can I use as a “glue” for vibration?

Electronics-approved RTV would probably be your best bet here.
Since this is a generator, I imagine hot glue may not be a good idea if the PCB is near a source of heat.
For moisture/condensation barrier, I think varnish might do the trick.. though you will probably have to do several coats to make sure there is a thick enough layer on there. Also also, make sure the varnish isn't corrosive.
Or, if you know of anything/any product that is more like rubber / protective coating but without being corrosive, then you can use that as well. I'm thinking something similar to car underbody tar (used for rust prevention) may work possibly?

Originally Posted by PM5K

Lastly, I’ve heard a good way to make caps more resilient is to up the voltage but keep the same capacitance

Well, there is some truth to that, but this is really too simplistic of a notion.

To answer your question in more details...
Yes, increasing the voltage rating does make the caps somewhat more resilient. This has to do with the fact that using a capacitor with a higher voltage rating means the capacitor will be physically bigger... when comparing two capacitors of the same brand and series ONLY. Physically bigger cap = higher ripple current rating and lower ESR rating. So for a circuit that tends to stress the caps more, the bigger cap will be stressed less, because it has higher RC rating.

Of course, if the original cap was not adequate to handle the requirements of the circuit, then using a cap from the same brand, series, and capacitance (but with a higher voltage rating) may not necessarily last that much longer if it too isn't adequate to handle the requirements of the circuit.

So the notion that increasing the voltage rating alone without paying attention to the brand or series of the capacitor is flawed. Take for example the VZ series from Nichicon VZ, which are known good and reliable general purpose caps. Let's take the 16V, 1000 uF cap from this series in 10x16 mm can size. It is capable of handling only 560 mA of ripple and rated for 2000 hours at 105C temperature. Now compare it to Nichicon HW of the same voltage, capacitance, and physical size: it is capable of handling 2000 mA RC, and rated for 10000 hours lifetime at 105C. So the cap from the HW series will last substantially longer than the VZ cap and/or handle much more abuse. In fact, the above HW cap will outlast even a 50V-rated cap of the same 1000 uF capacitance from the VZ series, despite the much higher voltage rating of the VZ cap.

So in fewer words... the answer is: it depends.

In the case of your inverter, the reason the original caps failed is probably because they were a garbage brand to begin with. If they were from a known good and reliable brand, they could have still been OK. Of course that also depends on the circuit design too and how hard it was pushing the original caps. But generally speaking, when dealing with unknown/cheap/crap brands, the reason they fail is because they are crap to begin with and not because the circuit was stressing them that hard.

So if you use a known good reliable brand, you won't have to increase the voltage rating, and these caps will still likely last much longer.