Author Topic: Beier 318L 12/24v DC Chest Fridge/Freezer -Blown Caps  (Read 791 times)

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Offline OTG

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Beier 318L 12/24v DC Chest Fridge/Freezer -Blown Caps
« on: October 13, 2017, 12:16:18 am »
Hey Y'all,

My two Beier 318L DC Chest Fridge/Freezers (I use 1 as a Fridge & 1 as a Freezer - link below for reference) use a Domus T34K Compressor with a Controller that hangs off the side of it. The Controller has a 1000uF 35V High Temp (105 Deg C) Electrolytic Capacitor, which unfortunately for me, keep blowing their tops... visibly raised with capacitance reduced to about 450uF. I've had to replace two after about 18months use, it seems that they are gradually degrading to the point where the fridge wont start (you can hear it click 3 times trying to start but it just can't turn over - then it gives up).

These are presently running off the load side  of a cheapie 24v 30A  Powertech MPPT charge controller. The controller seems to pause charging about once every couple of minutes to check the array voltage and find the MPPT - aka a "sweep & sleep". Each "pause" drops the voltage across the controller (load side too) and if the Fridge/Freezer are running there's a corresponding and notable dip in the compressors hum. I suspect it's this regular dip and rise in voltage which is killing the caps.

So I'm wondering:
1. Maybe if I just wire the Fridge/Freezer directly to the batteries (instead of through the load side of the controller) I can avoid/limit the effects of the sweep & sleep?
2. Could I use a different Capacitor that might better handle this? Perhaps a better Brand/Quality cap or a different spec/type (e.g. solid)?  The Controllers came with "DTDZ" brand caps, I've replaced them with "JWCO" brand caps I got off eBay... both just Chinese cheapies I think. Will be interesting to see how long the JWCO's last...

Any thoughts, advice or links to better caps appreciated!  :)

Offline DJ

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Re: Beier 318L 12/24v DC Chest Fridge/Freezer -Blown Caps
« Reply #1 on: October 13, 2017, 05:13:27 am »

I'd try using higher voltage caps. 64V or whatever they come around that.  Have had a few things blow caps and they were cured by just using higher voltage of the same rating.

Offline MadScientist267

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Re: Beier 318L 12/24v DC Chest Fridge/Freezer -Blown Caps
« Reply #2 on: October 13, 2017, 11:30:54 am »
A few things come to mind...

1 - Wiring across the batteries will help with the compressor tendency to stall, which is hard on just about everything in the mix because they need to draw more than normal current to get back up to speed.

2 - Replacing the caps with a higher voltage "equivalent" will help the caps handle transients they experience during normal switching that occurs while driving the compressor motor(s) - To a point. Generally speaking a higher voltage cap of identical capacitance will have a higher ESR, which means they will generate more heat internally... In the case of electrolytics, this will try to drive the moisture out of them sooner, making them age quicker, bringing it somewhat full circle. Generally, I go for the next voltage up as a balance. IOW, if the original calls for 16V, replace with 25. If original is 25, replace with 35... original 35, go with 50, and so on.

3 - Applying so-called "bypass" caps across each electrolytic will help them handle normal switching transients more efficiently. This is usually best done by soldering them *directly* across each electrolytic, with the leads as short as possible, on the foil side of the board in a one-for-one relationship. By forcing the highest frequency switching currents around the 'lytics, these spikes won't be dissipating as much energy inside the caps (hence the name "bypass"). Small tantalum caps on the order of a couple uF each are usually sufficient for this purpose, and at the lower voltages we're talking about here, really are ideally suited for the job.

4 - Keep things cool by adding a fan if necessary.  Even if the air circulating over the board isn't as cool as it should ideally be, any circulation is better than plain convection (which by definition requires heat to work) and will help.

5 - Increase the overall capacitance. This can be tricky because of space requirements, but if possible, up the total capacitance by increasing the cap count. It's better to use more of a smaller value than a single large cap to do this, as part of the goal here is to reduce the overall reservoir impedance, not just store more energy. A reservoir that can't deliver the necessary current when the transistors call on it to give the next push, isn't able to do it's job efficiently, and as mentioned above, will generate heat, and prematurely age the caps. Also, it will do you little good to pile up a bunch of caps on a couple of leads running to the original reservoir cap traces on the board. Inductance and resistance will largely negate your intent, so this one may be only minimally practical, if at all, in many cases. It depends on the board layout and how closely you can slip them together at the location of the original caps.

Ideally you'd do some combination of all of the above, but this isn't always practical, so you just have to go with what you can.

Hope this helps...
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Offline OTG

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Re: Beier 318L 12/24v DC Chest Fridge/Freezer -Blown Caps
« Reply #3 on: October 13, 2017, 06:19:05 pm »
Bloody brilliant advice, thanks fellas!

I like your 'combination of things' approach MS, thanks muchly for all the details.

The Controller does get rather hot hanging off the side of the compressor - the PCB is cased in a aluminium box with barely noticeable ribs on one side, - so it's a stretch to even say the controller is passively "cooled" when it's box basically just functions as a big heat sink for the compressor.  :P

I reckon I'll make a separate mount for the Controller - off of the compressor, add a small fan, higher voltage caps, and wire it across the batteries - should be much better!

Thanks again.  ;D

Offline OTG

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Re: Beier 318L 12/24v DC Chest Fridge/Freezer -Blown Caps
« Reply #4 on: August 17, 2018, 08:54:38 pm »
I'm admittedly pretty slack at this forum thing, but thought I'd post a quick update for others future reference/to close this topic out.

In summary, I:
  • Cut an angle bracket to fit the controller as a separate mount, off of the compressor,
  • Added a couple of cheap black anodised aluminium heat sinks to the top of the controller (conveniently, the Cap sits just under these), (unfortunately the thermal paste was  terribly oily/runny - wont be buying that one again!),
  • Wired in a 90mm fan for active cooling (at the bottom of the photo),
  • Swapped in 50V caps,

And it's been running like a champ ever since!  :) I also got rid of that rubbishy Powertech charge controller and I'm now using a Tracer unit, per It's still wired through the Controller, but it runs noticeably smoother through the Tracer and doesn't stall anymore (I think the Powertech's "sweep & sleep" was really hard on appliances for whatever reason).

If problems do pop up again, then I'll make the leap to wiring across the batteries. Otherwise it's looking good - thanks again for the advice fellas!