| Voltage Drop Calculator |
I had this page in another section, but decided that it might be better suited under the Power Supply section, because it deals with the transmission of power over long lines.
The calculations assumes uncoated copper or aluminum conductors operating at the temperature selected and is based on the ac/dc resistance or impedance from NEC 2005 Tables 8 and 9 for stranded conductors operating on a DC or AC 60Hz system. The ampacity of each conductor size in the dropdown menu below is based on NEC 2005 Table 310.16 for 60C insulated conductors rated 0 through 2000 volts with not more than three current carrying conductors in raceway, cable or earth with an ambient of 30C (86F).
The calculator below can help estimate the cable voltage drop in a power transmission system. Sometimes you only know the input and output voltages/current, but don't now what kind or size of wire to use in between. The procedure below is for initially setting up a power transmission system. In it, you first define the input parameters and output parameters. Then you adjust the cable specifications in between, until your overall voltage drop is less than 5%. Once you get your system defined, you can try other options to see how it affects system.
- Start by selecting the System Voltage (2 to 600 Volts) and System Type (DC, Single Phase 60Hz, Three Phase 60 Hz) on the left. This should be the line-to-line voltage for multi-voltage and 3 phase systems. For a 120/240V single phase system select 240V. For other single phase systems select the line-to-neutral voltage.
- Then, on the far right of the calculator, define your Cable Length, in feet or meters (one-way distance) and the expected Load Current, in amperes.
- Then define whether you are going to use 1, 2, 3, or 4 Parallel Runs of wire. Examples:
- 120/240V Single Phase System with single black-red-white conductors (installed in single conduit) select "single set of conductors"
- 120/208V 3- Phase System with 2 conductors per phase and neutral (installed in 2 parallel conduits) select "2 conductors per phase in parallel"
- DC System with 3 positive and 3 negative conductors select "3 conductors per phase in parallel".
- Now, under Conduit Type, select whether the cable is going to be in conduit and, if so, what type. If your not using conduit, just select No Conduit. NEC tables assume 75C operating temperature. If you oversize the conductor, in the next step, a lower temperature can be used. However, this temperature should always be higher than ambient.
- At this point you can define the Cable Size and Conductor Type. Higher current systems will require bigger cables (lower AWG numbers)
- Finally, check the calculated Voltage Drop. If the Voltage Drop Percentage is greater than 5%, try increasing the Cable Size (lower the AWG numbers).
The actual voltage drop may differ a little from the calculator's prediction, but will be very close, in most cases.
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| Examples |
Example 1
Say I have one of those weed/grass trimmers that uses thin plastic line. The trimmer is corded and is rated at 120 VAC @ 6.5 Amps. Obviously, to get to any distant areas, you might need a fairly long extension cord. For this example, say you need 100 feet. The question is, which extension is best? The #16, #14, or #12? The goal should be that you should not lose more than 5 % of your voltage, measured at the trimmer. If you enter the appropriate information in the calculator, it will show that using a 100 foot #16 gauge extension, there will be a 5.4 % voltage drop. That may be a little to much of a drop. But a #14 gauge extension will reduce that drop to 3.3 %, keeping it withing the manufacturer's operating range. That extension should be sufficient up to about 150 feet. But for any distance greater than 150 feet, it would be prudent to use a #12 gauge extension. Or, get a battery operated trimmer.
Example 2
Another example might be that you are installing a outlet, for a Motor Home, that needs to supply 120 Volts AC, 60 Hz, @ 30 Amps. The outlet will be 50 feet from the power box. But the new outlet may need to use a 25 foot extension, to reach the Motor Home. So for this example, the run to the outlet should be calculated with the extension in place. That would be 75 feet. As with the previous example, the goal should be that you should not lose more than 5 % of your voltage, measured at the Motor Home. If you enter the appropriate information in the calculator, it will show that using a 75 foot #12 gauge wire, there will be a 7.4 % voltage drop. That may be too much drop for some of the apliances in the Motor Home so a better choice would be #10 gauge wire. That would only produce a 4.5 % drop. Or, you could really be safe and use a #8 gauge wire, from the power box to the new outlet (2 % loss). That would allow the 25 foot extension to be a little lighter gauge.
| Battery Life Estimator |
W1PNS / WAØITP / AB8XA Battery Life Estimator (1)
Based on Jim Duffy's (KK6MC) Battery and Charging Systems White Paper (2)
Revised Aug. 10, 2011
Batteries and Charging Systems for QRP - Chocked full of facts and well worth reading.
| First, use this calculator to initially determine your requirements in Amp/Hours. Select one of the radios listed, or select "Other" and enter your own data. | |
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HW-8 - Receive: 90 mA, Transmit: 430 mA (CW Only) FT-817 - Receive: 450 mA, Transmit: 2A FT-857 - Receive: 1 A, Transmit: 22A IC-735 - Receive: 1.5 A, Transmit: 22A Other |
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| Duration needed in Hours: | |
| Mode Duty Cycle: | |
| CW 40%, SSB 20%, AM/FM 100%, RTTY/Digi 100% | |
| Operator Duty Cycle: % | |
| Radio's Receive Current: Amps | |
| Radio's Transmit Current (Amps): Amps | |
| Average Current Consumed: 605 mA | |
| A/H Capacity Needed: 3 A | |
| A/H Capacity + Reserve: 6 A |
| Then use this calculator to determine the length of time you will be able to operate, based on the Amp/Hour rating of your battery. | |
| Battery Amp/Hour Rating: | |
| Depth of Discharge (%): | % |
| Usable Battery Amp/Hours: | 4 |
| Expected Battery duration in Hours: (3) | 6.6 |
| Messages |
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(1) With WAØITP and AB8XA mods of the original W1PNS Spreadsheet.
(2) Presented at OzarkCon 2006 and Pacificon 2005.
(3) The greater the transmit draw is above the battery Ah Rating divided by 20, the lower the duration will actually be.
- Modified and Uploaded with KK6MC and W1PNS permission - WAØITP - 2 June 2011.
- Corrected and modified - AB8XA - 5 June 2011.
- Adapted for the "Web" - K5DCM - 13 June 2011.