The voltage rating makes a big difference in terms of size and may not provide you that much more in terms of performance. 10,000uf capacitors in a 50-60 volt range may fit your amp. Any way you could check out the size difference and trade them in if smaller voltage caps fit?
Need help on power supply caps
I recently bought new power supply caps knowing that they are larger in capacity and in phyical size . Because of limmited space in my amp if I solder them directly to the circuit board, they are to high to fit my cover on without cutting. I do have plenty of room to lay them down with about 3 inches of wire running from cap lugs to board. I read on blackgate web page that they strongly suggest no wires run from lugs . Also I am goig from 4200uf/47volts to 10,000uf/85volts Do I need to upgrade rectifier ? Any help would be great.
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There is a circuit board trace from the lug to whatever it connects to, so I don't think adding a few inches of wire would hurt. Besides, you really don't have a choice. The issue with bigger caps in the power supply is that the in-rush current when you turn it on will be higher, and you risk blowing a fuse or possibly a rectifier. Since your new caps are a little over twice the capacity of the old ones my gut feeling is that it will be OK. The exception would be if the design was poor in the first place and it was operating close to it's limits. I would go for it. |
P.S. You may wish to also check with the manufacturer -- obviously, power supplies are very complex. Here is an interesting read on some of the approaches that can be used: http://synergy.sager.com/ProductPDFs/PowerTransformer_FilterRatings.pdf#search='rectifier%20ratings%20power%20supply' |
If the amp has 35-amp/400V bridge rectifiers, it won't be a problem; if it's less than that (15, 20, 25-A), then see if it's possible to replace them with the 35-A, the largest rating available, if you want to be sure. I agree with Herman, the existing recitfiers should be okay, especially if the amp is rated at 50W or greater. |
Believe it or not, most electrolytics work best if run closer to their voltage ratings. I am NOT saying that you should run them up to their voltage limit, but that a lower voltage rating may actually perform better AND fit where the stock caps were. As Ozfly mentioned, 50 or 60 volt caps may actually be a drop in if the caps that you are replacing were of older vintage. Other than that, i see no problem with running small heavy gauge leads from the caps to the circuit board. In doing so, you may actually be able to improve current flow by routing the leads in a more direct lower resistance path through the use of heavier gauge wiring. Just make sure that the wire itself isn't stressed at the point of connection going into the board or you may end up with a poor connection. This would be due to age and solder fatigue. Due to the rigidity of the wire pulling on the joint all the time, the board can develop small fissures between the trace and the solder. Conductivity is reduced due to a lack of contact area and sooner or later, such a joint will mature into a break. Sean > |
Sean- I would agree especially with BGs you don't have to use the standard 2-3X the working voltage for the rated voltage on the cap. What's your feeling about bypassing the main power supply caps with a small film cap, and any recos on what brands you prefer? Oldcar63- Did you measure the working voltage on the 4200uf/47volts caps you're replacing? The BG STD4700/50 is a lot less money and would still be a big improvement. |
As a general rule, the larger the capacitor in value, the lower the ESR. ESR is basically the series resistance of the cap and we want to keep that as low as possible. If you can find ESR specs for various caps, take that into consideration when shopping around. As far as bypassing high value caps, i see no problem with doing so. I typically prefer to run multiple different values of caps if possible. Rather than just run one huge cap ( etc ) with a bypass cap, you can use several smaller caps of various ratings that equal the same appr value. By staggering their values, you stagger their charge / discharge rates and create a more effective filter over a wider bandwidth with less ripple. In the array of caps used, one can easily mix in some smaller values that would act as a bypass for the larger value caps. The problem with doing so is that it can become rather unsightly i.e. a bunch of different sized caps, both in length and in diameter, sticking up all over the place. This is both a more costly route to go and more time consuming, hence the lack of commercial products that utilize such an approach. As a hands on DIY type of installation though, there's nothing from stopping someone from going this route other than time, patience and space within the unit itself. Sean > |
If it is a solid state device, leave it powered up 24/7 for a couple of days. Turn the device off, unplug it from the wall and then turn the device back on. Leave it turned on but unplugged for a good period of time as you want to fully discharge the caps. Turn the device back off and then plug it back in. Turn it on and leave it powered up 24/7 for several more days. Repeat the above once again a few days later. This will help the caps to fully form and settle in. After repeating this cycle two or three times, you'll be over 90% of the way there. The remaining settling will occur over time due to thermal cycling and dynamic stress during normal use. Sean > |