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| 120VDC in to appliances and devices? |
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| AVGresponding:
--- Quote from: lufihengr on September 07, 2023, 03:22:33 pm ---As a followup then, is there a point where it would just be easier/better to use DC power from batteries to spin a DC motor, that is connected to a generator? That would at least be a perfect sine wave :D As you have probably gathered, the situation is a case where grid connection is not available, but the use of regular appliances is wanted. --- End quote --- Depending on funds, a better solution might well be solar PV/a wind turbine and a decent inverter, or indeed a generator. |
| Zero999:
--- Quote from: lufihengr on September 07, 2023, 03:22:33 pm ---As a followup then, is there a point where it would just be easier/better to use DC power from batteries to spin a DC motor, that is connected to a generator? That would at least be a perfect sine wave :D As you have probably gathered, the situation is a case where grid connection is not available, but the use of regular appliances is wanted. --- End quote --- That's known as a motor-generator set and is the old fashioned way of doing it. Quite often the primary and secondary windings were on one armature, in which case it was known as a rotary converter. Imaging a DC motor, with three poles on the armature, each with a secondary winding, connected to a slip ring. The DC going to the commutator will be converted to three phase AC. The disadvantages of motor generator sets are: low efficiency, more noise and higher maintenance, as bearings and brushes need to be replaced. The only advantages are they're more electrically robust and can withstand ionising radiation better than electronics. Nowadays static, semiconductor inverters are used. A boost converter, takes the battery voltage up to the peak voltage of the AC output and an H-bridge converts it to AC. Cheap inverters produce a modified sine wave, whilst more expensive ones use PWM and a filter to give a pure sine wave. The only downsides are they're more vulnerable to over-voltage and ionising radiation, compared to motor generator sets. If all you want to do is convert one DC voltage to another, use a DC to DC converter. |
| Siwastaja:
I have ran random switch-mode stuff out of DC and usually it just works. BUT: --- Quote from: Berni on September 07, 2023, 12:28:39 pm ---The diodes won't be run that close to the rating to be a problem. --- End quote --- That's quite an assumption. Cheap consumer electronics is often dimensioned close to destruction. Diodes specifically are annoying to design in because they dissipate surprisingly lot of power for quite small packages. Suddenly doubling (+100%, not something like +10%) the average power dissipation in a component is something I would not classify as "definitely no problem". I would keep an eye on it, or just bypass the bridge. |
| Zero999:
I think assuming the diodes are over specified is sensible with small power supplies, given 400V parts normally have current ratings of at least 1A. Does it really increase the power dissipation in the diodes that much? Don't forget that although the diodes only run at 50% duty when on AC, the peak currents are much higher, in a non power factor corrected design, whilst with DC it's more constant. I suspect the it's not that bigger difference. |
| langwadt:
--- Quote from: Siwastaja on September 07, 2023, 06:10:49 pm ---I have ran random switch-mode stuff out of DC and usually it just works. BUT: --- Quote from: Berni on September 07, 2023, 12:28:39 pm ---The diodes won't be run that close to the rating to be a problem. --- End quote --- That's quite an assumption. Cheap consumer electronics is often dimensioned close to destruction. Diodes specifically are annoying to design in because they dissipate surprisingly lot of power for quite small packages. Suddenly doubling (+100%, not something like +10%) the average power dissipation in a component is something I would not classify as "definitely no problem". I would keep an eye on it, or just bypass the bridge. --- End quote --- but with ac the diodes are carry a higher peak current at the peaks of the period, with DC the diodes carry current all the time but it must be lower |
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