how to reduce surge current of motor?

2»

Comments

  • mike95490mike95490 Solar Expert Posts: 8,469 ✭✭✭✭✭
    Re: how to reduce surge current of motor?
    ......You might need a bigger inverter.

    Or a stouter set of batteries, or DC feed cables. At the high starting currents, the DC amps can become amazingly high, and then you start loosing volts in the battery internal resistance and battery wires.

    My 1/2 "hp" pump consumes 1KW from the inverter, when theory suggests it should only draw about 400w. I can't measure it's starting current, but at 240VAC my 6Kw inverter does not complain.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: how to reduce surge current of motor?
    mike95490 wrote: »
    Or a stouter set of batteries, or DC feed cables. At the high starting currents, the DC amps can become amazingly high, and then you start loosing volts in the battery internal resistance and battery wires.

    My 1/2 "hp" pump consumes 1KW from the inverter, when theory suggests it should only draw about 400w. I can't measure it's starting current, but at 240VAC my 6Kw inverter does not complain.

    Ditto.
    My "1/3 HP" pump runs 800+ Watts in reality (PF on these motors tends to be awful) and the start-up is about double that. My 3.5 kW inverter has no problem starting it at all. If I try to run it from the 1.6kW generator however, it faults the gen on start.
  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭
    Re: how to reduce surge current of motor?

    Most 1000watt pure sine wave inverters aren't really 1000watt pure sine wave, or if they are they just heat up.

    The whole pure sine wave "mobile" industry is fairly inaccurate to efficiency standards. My 1000watt pure sine wave inverter reacts, like a 800watt pure sinewave with 1600watt peak surge, not 1000watt pure sine wave with 2000 peak surge. have 16" of 4AWG between the inverter and the battery. All these inverters made in china and rebadged aren't what they seem.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: how to reduce surge current of motor?
    Most 1000watt pure sine wave inverters aren't really 1000watt pure sine wave, or if they are they just heat up.

    The whole pure sine wave "mobile" industry is fairly inaccurate to efficiency standards. My 1000watt pure sine wave inverter reacts, like a 800watt pure sinewave with 1600watt peak surge, not 1000watt pure sine wave with 2000 peak surge. have 16" of 4AWG between the inverter and the battery. All these inverters made in china and rebadged aren't what they seem.

    Agreed. I've tested a few of these myself and found them lacking in their rated power. Seems like they meet that output standard in lab conditions but not in the real world. And the surge ratings are often for such a short period of time as to be meaningless. 2kW for a millisecond isn't much good.
  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭
    Re: how to reduce surge current of motor?

    My 1000watt invert is on a 90AMP AGU fuse, and the fuse wont blow, that alone tells you its not a true 1000watt inverter.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: how to reduce surge current of motor?
    My 1000watt invert is on a 90AMP AGU fuse, and the fuse wont blow, that alone tells you its not a true 1000watt inverter.

    It has been my experience that the inverter will fault before a fuse will blow.
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: how to reduce surge current of motor?

    Exactly as Cariboocoot says. The fuse is only a last resort, for when there is a major fault and major shorts within the inverter, regardless whether PSW or MSW.
    It takes time for a fuse to blow. In the meantime, the internal electronics, if working properly, protects the inverter by shutting it down on overload when necessary, way before the fuse ever blows.
    If the fuse ever blows, you've got far more problems than an overload on the output.
  • mike95490mike95490 Solar Expert Posts: 8,469 ✭✭✭✭✭
    Re: how to reduce surge current of motor?

    And I always thought the transistors were there to protect the fuse !
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: how to reduce surge current of motor?
    mike95490 wrote: »
    And I always thought the transistors were there to protect the fuse !

    No no, not the transistors, it's the capassitaters and oskilators that do that! :D
  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭
    Re: how to reduce surge current of motor?

    You guys are too funny!
    When I first bought the wirng kit for the inverter it came with an 80amp fuse and didn't have time to source for a 100amp fuse. The 80amp fuse blew after my 4th time of use on heavier equipment, so I am under the impression that the inverter will demand 80 amps. It wont blow a 90 amp fuse the demand the inverter requires will draw roughly 80amps. Of course it is pobably better to use a shunt on the negative conductor to determine the exact draw required for the inverter but I will say that it needs close to 80 amps regardless if the battery has 13.7V or 11V for operation of the inverter.

    13.7 X 80 = 1096 watts then there is a 10 % conversion loss for AC output

    1096 X.10=109.6

    So there is a 109.6 watt loss for AC output

    So my 1000 watt inverter will only output 900.4 watts if the battery is 100% full, that number becomes smaller as the battery DOD and temperature of the battery rise from heavy use.

    If I take the average range of operation that the inverter performs to according to the incoming DC voltage range I come up with 12.25 V

    12.25V X 80=980 watts
    980 X.10= -98watts
    900watts AC output


    AC output is roughly 900 watts not 1000watts pure sine wave as advertised. I'm not even accounting for temperature losses or long duration cycling which the inverter actually performs to 800watts according to the front kVA display monitor I have after using it for 10 to 20 minutes constantly.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: how to reduce surge current of motor?

    Yes as the battery Voltage goes down the current to supply a given output Wattage goes up. And you have to allow for the inverter's own consumption and conversion efficiency.

    So if you work backwards 1000 Watts AC is about 1111 Watts on the DC side and the inverter itself will be drawing, say, 10 Watts so the draw on the battery at full power is more like 1120 Watts.

    Then you have the Voltage range the inverter will operate in, which is often 10.5 to 15 Volts. Full power at 15 Volts is only 75 Amps but full power at minimum Voltage is 107 Amps. Pretty wide range.

    And that doesn't account for Voltage drop and wiring loss.

    The ones I tested had trouble with 13.8 VDC supply through 0000 AWG wire. Now that's poor performance!

    I don't know, maybe they super-cool the labs where they test these things. Or do it outside in the Cariboo in Winter. Same thing. ;)
  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭
    Re: how to reduce surge current of motor?

    Then you have the Voltage range the inverter will operate in, which is often 10.5 to 15 Volts. Full power at 15 Volts is only 75 Amps but full power at minimum Voltage is 107 Amps. Pretty wide range.

    The spec on my inverter is very limited says it will operate between 15V and 11V DC. The inverter will throw trouble code and standby once the battery reaches the 11V discharge.

    I don't find that spec to be to bad so I don't have to worry so much about the inverter fully draining the battery.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: how to reduce surge current of motor?
    The spec on my inverter is very limited says it will operate between 15V and 11V DC. The inverter will throw trouble code and standby once the battery reaches the 11V discharge.

    I don't find that spec to be to bad so I don't have to worry so much about the inverter fully draining the battery.

    That's actually better than most for LVD. Really even 11 Volts can be a problem for the battery. Especially since people assume it's meant to operate down to that level as a matter of course.
    Naturally when you get into the expensive inverters they have programmable low and high disconnect. You've probably read my remarks on using system nominal Voltage as the LVD point.
  • WalterkWalterk Registered Users Posts: 6
    Re: how to reduce surge current of motor?
    vtmaps wrote: »
    I'm thinking that the combined load of the pump and the furnace is too much for the generator. Are your pump and furnace 120 volts or 240 volts? if they are 120 volts, how are they wired from the generator (are they on opposite legs of the split phase power)?

    --vtMaps
    pump is 230V so using both legs of split power, furnace 120 so using one of the 2 legs
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: how to reduce surge current of motor?

    One possible solution, depending on how your furnace would tolerate it, would be to have a relay wired with the pump motor, that would cut power to the furnace when the pump needed to run. That way the genny wouldn't have to stress itself trying to run both at once.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: how to reduce surge current of motor?
    One possible solution, depending on how your furnace would tolerate it, would be to have a relay wired with the pump motor, that would cut power to the furnace when the pump needed to run. That way the genny wouldn't have to stress itself trying to run both at once.

    Might be better the other way 'round as furnace controls don't want to be suddenly interrupted. Especially not hot air ones, for which sudden loss of power can be damaging if repeated over time (does not allow proper cool down of the plenum).
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: how to reduce surge current of motor?

    Good point Coot, and the way to go for sure if the user can wait till the furnace stops to get water. A perhaps shorter wait would be to have a second relay open the thermostat so the furnace would start cooling down as soon as the pump wanted to run, then when the fan finally stopped, the pump could go..
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: how to reduce surge current of motor?
    Good point Coot, and the way to go for sure if the user can wait till the furnace stops to get water. A perhaps shorter wait would be to have a second relay open the thermostat so the furnace would start cooling down as soon as the pump wanted to run, then when the fan finally stopped, the pump could go..

    Sounds like that would cover all the bases. :D
  • Doctor DipDoctor Dip Registered Users Posts: 1
    I understand your question. If you can get past the initial startup the inverter will drive the pump nicely. Without knowing exactly what the design of your pump motor is I will proceed with an assumption or two.

    Single phase AC motors must create an artificial phase displacement to initiate the rotation of the stator. To do this there are two coils, a start coil and a drive coil. They are physically located at different angular positions to each other. So far so good but now they need to be out of phase with each other, so a capacitor is connected to the starting coil. At start up the electrical phase displacement caused by the greatly leading power factor of the starting coil relative to the drive coil transposes to a mechanical phase displacement of rotational forces with respect to time. In short if you like the magnetic fields created by the stator coils provide a 'kick' at slightly differfent moments, approx. 10 ms apart in fact. This is sufficient to overcome the inertia and the momentum of the rotor allows the motor to spin up.
    The inrush current is caused by the capacitor but also by the magnetizing current inrush.

    I would suggest that a possible solution could be the use of NTC resistance in series. These devices are manufactured with a higher resistance at ambient air temperature and as they pass current exhibit a heating effect due to the current flowing through them. As the temperature of the device increases the resistance reduces. The typical range would be from 200 ohms to less than 1 ohm. NTC stands for 'negative temperature cooefficient' and is the opposite of the effect of a normal increase of resistance with temperature of most resistive materials such as nichrome or copper. Theoetically at least this should dampen the inrush current. What I cannot say is if it will start your pump, I guess you will need to experiment with NTC devices with different characteristics.
    I have not yet tried this experimentally but if anyone has one so, I for one would like to know the results.

  • jonrjonr Solar Expert Posts: 1,327 ✭✭✭✭
    I experimented with NTC thermistors on a refrigerator and they worked reasonably well. It's documented on this forum somewhere.

    I've heard reliable reports that having another motor running while starting a second motor can help with startup loads. But it may be only for conventional generators (where RPM and frequency drop occurs).

    I am available for custom hardware/firmware development

Sign In or Register to comment.