I need 75V 10,000uF capacitors for a four channel leach amplifier I am building. I will have two 750va toroids. Voltage rails will be + and - 58V dc
I cant seem to find 75V caps. I did find 10,000uF 50V caps at a very cheap price thought. I am thinking - wiring two caps in series for 100V.
Something just doesn't feel right about it. Please comment on this!
I cant seem to find 75V caps. I did find 10,000uF 50V caps at a very cheap price thought. I am thinking - wiring two caps in series for 100V.
Something just doesn't feel right about it. Please comment on this!
If you put two 10000uF caps in series, the total cap value will be 5000uF. Place two of these pairs in paralell, and you end up with a total of 10000uF. You will need 4 10000uF/50V to make 1 10000uF/100V.
Make sure that you put bleeder resistors in paralell with each cap, say 1-10k or something. You figure out how much power you will be wasting.
That way, you make sure that the DC-voltage will be the same over each cap.
Make sure that you put bleeder resistors in paralell with each cap, say 1-10k or something. You figure out how much power you will be wasting.
That way, you make sure that the DC-voltage will be the same over each cap.
You may connect them in series but there are two points to take into account :
- Resulting capacitance of 10mF + 10mF in series will be 5mF and, for example, eight 10mF 50V units would be required to get 20mF 100V [and another eight units for the other rail]
- Each capacitor has his own leakage current and you would need to place bleeder resistors of equal value [low enough] in paralell with each half of each bank to ensure DC balance. This is a common thechnique employed in power supplies
- Resulting capacitance of 10mF + 10mF in series will be 5mF and, for example, eight 10mF 50V units would be required to get 20mF 100V [and another eight units for the other rail]
- Each capacitor has his own leakage current and you would need to place bleeder resistors of equal value [low enough] in paralell with each half of each bank to ensure DC balance. This is a common thechnique employed in power supplies
Bleeder Resistors
I use 3K 3W resistors for a design where I needed 12000 uFd at 120V. I use 4 12000 uFd 63V caps in series parallel. However, if you submit the amplifier for regulatory approval, they will short one capacitor. The other one in series will vent and they will fail the unit.
You can only series caps if the unit will not be sent in for regulatory approval.
I use 3K 3W resistors for a design where I needed 12000 uFd at 120V. I use 4 12000 uFd 63V caps in series parallel. However, if you submit the amplifier for regulatory approval, they will short one capacitor. The other one in series will vent and they will fail the unit.
You can only series caps if the unit will not be sent in for regulatory approval.
You may add a protection circuit, disconnecting power supply in case of overvoltage on any capacitor bank, to pass such nonsense tests [some people in this world seem to have nothing better to do than shorting 12mF charged to 120V, ie : 86 Joules 
and they even charge thousands of $$$ for doing so 
]
and they even charge thousands of $$$ for doing so ]Nonsense Test
Those people who do these nonsense tests have the organizational names of CSA and UL and unfortunately, as the result of such a nonsense test, can deny you the ability to sell your product. I have had since then to redesign a perfectly good power supply to use 4 x 2700 uFd 160V capacitors in ra egular parallel arrangement. However the 160V parts have much longer lead times but that's not their problem. The extra circuitry to cut off the power in case of an really serious unbalance was an alternative but they consider that a crutch and if you use it, they will find a different reason to fail you.
Those people who do these nonsense tests have the organizational names of CSA and UL and unfortunately, as the result of such a nonsense test, can deny you the ability to sell your product. I have had since then to redesign a perfectly good power supply to use 4 x 2700 uFd 160V capacitors in ra egular parallel arrangement. However the 160V parts have much longer lead times but that's not their problem. The extra circuitry to cut off the power in case of an really serious unbalance was an alternative but they consider that a crutch and if you use it, they will find a different reason to fail you.
How the seals got there?
Exactly. I wonder about that too but CSA rejected me for having series capacitors and I had to change the design to be accepted. Maybe because my unit was over a certain power threshold. My amplifier is over 1000W. Regardless, I got the impression thet were making up tests until it failed on something as if they were obliged to fail us on something. This after we spent thousands of dollars on a consulting engineer who supposedly knew what was needed for us to pass and he vetted the design, had me make some changes and pronounced it as ready to pass on first try.
While no one wants to make an unsafe product, it seems to me that the inspectors must get brownie points for failing products then they charge us a pile more money for retests.
They also reject many of the parts I selected in spite that all these parts are already CSA/UL approved. My transformer primary connector was rejected for 230V operation in spite of the fact it was already CSA approved for 600V AC operation. I use UL approved relays on the secondary side and they were rejected because they wanted a different UL approval on them. In spite of the fact the relays I was using were being used within spec.
Quite frustrating. Agency approval, for a smaller company with limited engineering resources can add over a year to getting the product out the door. It seems that no matter what we do, the product will be rejected the first time through. However, we have learned to not argue and do whatever they say. If you do argue, you are told that they don't make the rules and you can appeal it to a rules commitee that meets once a year or something and they have their docket filled for several years. Instead, you just do what they say and incorporate everything they say into the next product and see what they come up with next time to reject you.
Exactly. I wonder about that too but CSA rejected me for having series capacitors and I had to change the design to be accepted. Maybe because my unit was over a certain power threshold. My amplifier is over 1000W. Regardless, I got the impression thet were making up tests until it failed on something as if they were obliged to fail us on something. This after we spent thousands of dollars on a consulting engineer who supposedly knew what was needed for us to pass and he vetted the design, had me make some changes and pronounced it as ready to pass on first try.
While no one wants to make an unsafe product, it seems to me that the inspectors must get brownie points for failing products then they charge us a pile more money for retests.
They also reject many of the parts I selected in spite that all these parts are already CSA/UL approved. My transformer primary connector was rejected for 230V operation in spite of the fact it was already CSA approved for 600V AC operation. I use UL approved relays on the secondary side and they were rejected because they wanted a different UL approval on them. In spite of the fact the relays I was using were being used within spec.
Quite frustrating. Agency approval, for a smaller company with limited engineering resources can add over a year to getting the product out the door. It seems that no matter what we do, the product will be rejected the first time through. However, we have learned to not argue and do whatever they say. If you do argue, you are told that they don't make the rules and you can appeal it to a rules commitee that meets once a year or something and they have their docket filled for several years. Instead, you just do what they say and incorporate everything they say into the next product and see what they come up with next time to reject you.
This point is where I was triying to go
Regulatory agencies are more focused in money issues than in safety issues. If they didn't make enough profit, then the would disappear, products of small companies never get approved at the first time
In the other hand, these agencies are a mechanism employed by big manufacturers to Eliminate Minor Competitors [this is the actual meaning of E.M.C. initials, they have nothing to do with electromagnetic stuff as most people is fooled into thinking]
Regulatory agencies are more focused in money issues than in safety issues. If they didn't make enough profit, then the would disappear, products of small companies never get approved at the first time
In the other hand, these agencies are a mechanism employed by big manufacturers to Eliminate Minor Competitors [this is the actual meaning of E.M.C. initials, they have nothing to do with electromagnetic stuff
as most people is fooled into thinking]
Capacitors follow the opposite rule to resistors when you combine them. In parallel, capacitance adds, in series it reduces and is the reciprocal of the sum of the reciprocal values of each capacitor.
So when you put two 36mF caps in series the combined cap is 18mF. When you put two series sets in parallel the combined cap is 36mF again.
The voltage rating remains unchaged for caps in parallel and adds for caps in series IF AND ONLY IF the voltage rating of each series cap is not exceeded when the caps charge up and down. The voltage that develops across each cap is proportional to the integral of the current flowing through it multiplied by the reciprocal of the capacitance. With caps in series they all experience the same current flow, so the voltage across each cap will be proportional to their capacitance.
Ex, two caps a and b, in series with capacitance Ca and Cb. They are charged so that the total voltage across them is V. The voltage across a will be Va = b/(a+b), and Vb = a/(a+b).
So if both caps are exactly the same capacitance the voltage across them will be equal and half of the total voltage.
Note: you have to be careful about this when putting two caps in series who's voltage rating is the same but who's capacitance is different. Say you put 20mF 50V in series with 10mF 50V. You cannot charge the two up to 100V! The smaller cap voltage will increase more quickly than the larger; when the 10mF cap has 50V across it the 20mF cap will only have 25V across it: so the maximum total voltage is 75V (not 100V).
The balancing resistors are needed because you cannot be sure the two 36mF 40V caps are exactly 36mF each. Big caps often have tolerances no better than 20%. So one could be as high as 43mF and the other as low as 29mF. If this were the case then when they are charged up to 80V the smaller would have 48V across it and the larger only 32V. The 29mF cap would exceed its voltage rating. A resistor is added in parallel with each cap to try to balance the voltages by diverting current flow past the caps in inverse proportion to the voltage imbalance.
Working out the optimum value of the resistors is not simple, especially when the current flows are as dynamic as they are with music. I would advise that you design for safety assuming no resistors. For the 43mF and 29mF caps in series the max will be when the 29mF has 40V across it and the 43mF has 27V across it, giving a total of 67V. Use the series combination for a psu of 67V or less (not for 80V). Add balancing resistors as well to help keep the caps balanced.
So when you put two 36mF caps in series the combined cap is 18mF. When you put two series sets in parallel the combined cap is 36mF again.
The voltage rating remains unchaged for caps in parallel and adds for caps in series IF AND ONLY IF the voltage rating of each series cap is not exceeded when the caps charge up and down. The voltage that develops across each cap is proportional to the integral of the current flowing through it multiplied by the reciprocal of the capacitance. With caps in series they all experience the same current flow, so the voltage across each cap will be proportional to their capacitance.
Ex, two caps a and b, in series with capacitance Ca and Cb. They are charged so that the total voltage across them is V. The voltage across a will be Va = b/(a+b), and Vb = a/(a+b).
So if both caps are exactly the same capacitance the voltage across them will be equal and half of the total voltage.
Note: you have to be careful about this when putting two caps in series who's voltage rating is the same but who's capacitance is different. Say you put 20mF 50V in series with 10mF 50V. You cannot charge the two up to 100V! The smaller cap voltage will increase more quickly than the larger; when the 10mF cap has 50V across it the 20mF cap will only have 25V across it: so the maximum total voltage is 75V (not 100V).
The balancing resistors are needed because you cannot be sure the two 36mF 40V caps are exactly 36mF each. Big caps often have tolerances no better than 20%. So one could be as high as 43mF and the other as low as 29mF. If this were the case then when they are charged up to 80V the smaller would have 48V across it and the larger only 32V. The 29mF cap would exceed its voltage rating. A resistor is added in parallel with each cap to try to balance the voltages by diverting current flow past the caps in inverse proportion to the voltage imbalance.
Working out the optimum value of the resistors is not simple, especially when the current flows are as dynamic as they are with music. I would advise that you design for safety assuming no resistors. For the 43mF and 29mF caps in series the max will be when the 29mF has 40V across it and the 43mF has 27V across it, giving a total of 67V. Use the series combination for a psu of 67V or less (not for 80V). Add balancing resistors as well to help keep the caps balanced.
In the real world, the real unbalance problem is caused only by different leakage currents. AC components across each capacitor hardly exceed 5V p-p so 20% mismatch of dynamic parameters between capacitors is not a problem
Anyway, +20% -5% typical tolerances for electrolytics are usually specified for full temperature or voltage ranges. When both capacitors work at the same temperature, same charging voltage and same aging conditions, mismatches tend to be much smaller
Anyway, +20% -5% typical tolerances for electrolytics are usually specified for full temperature or voltage ranges. When both capacitors work at the same temperature, same charging voltage and same aging conditions, mismatches tend to be much smaller
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