Capacitor for my Dishwasher?

chevenstein
chevenstein Solar Expert Posts: 100 ✭✭
I have a dishwasher with electronic controls (ugghh) that likes to shut off in the middle of washing the dishes sometimes when the well pump cuts in and the voltage drops. I'm assuming that the digital control board is loosing power for long enough to reset and that this isn't some other problem. I've looked into retrofitting a mechanical timer but found that I would have to fabricate a new wiring harness. I've also looked into trading my unit for one with a mechanical timer but have not found a decent trade.

Usually the DC power supply on boards like this has a transformer, rectifier, and capacitor to reduce the incoming AC ripple; if I were to increase the capacitance on this circuit where the de-rippling cap is attached could I theoretically get the board to ride out the low voltage conditions? Note: I know just enough about this sort of thing to be dangerous...

Any comments or thoughts would be greatly appreciated!

PS - No, washing the dishes by hand is not an option. My wife and I are rather odd when it comes to some things, washing dishes being one of them (we don't currently even have a kitchen sink!).

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Capacitor for my Dishwasher?

    This is probably not the answer you want. :p

    If we are talking about an off-grid system with an inverter powering the dishwasher and the water pump which, when the pump comes on, the AC Voltage drops enough to cause the digital control of the dishwasher to fault out ... You have a severely under-sized system. Either the inverter isn't large enough to handle the load or the batteries/wires are permitting too great a Voltage drop on the DC side. Rather than muck about with the dishwasher, wouldn't it be better to get the AC up to snuff?
  • chevenstein
    chevenstein Solar Expert Posts: 100 ✭✭
    Re: Capacitor for my Dishwasher?

    PPS - The dishwasher is a Whirlpool DU945PWSQ0 and the dips in power are rather substantial (not sure how low, but the lights get pretty dim). I've also considered a giant well pressure tank but we don't have the indoor space for it (too cold in winter to have outside). I suppose I could also replace the well pump with something that starts more softly but that would be a bigger ordeal than retrofitting a mechanical timer to the DW.
  • chevenstein
    chevenstein Solar Expert Posts: 100 ✭✭
    Re: Capacitor for my Dishwasher?

    Cariboocoot - no, that's a perfectly reasonable answer. We are still using the 'training' batteries (8 golf cart T105 clones), so a larger (2X size) battery bank is on the horizon, however the bank does power everything else without issue. I think the larger problem is the well scenario; here's some background:

    The off grid system consists of (currently) 8 T105 clones, a Magnum MS4448AE inverter, and 1.5KW of solar. This is more than adequate for our needs 9 months of the year (usually floating by noon, load shifting gets us by with very little generator use in the warmer months). The generator is a 7KW LP unit.

    The well is a problem, as it's 400+ feet deep and the pump is near the bottom. The well was already installed when we acquired the land (was for a hunting camp) so I didn't have a choice in the pump or know its specifications (it is a controller-less model; even more starting load). I did measure the pump starting with a borrowed Fluke meter that has a motor inrush mode and it registered about 28 amps per leg starting, 7 per leg running. On the DC side this is (according the the less accurate on DC Fluke) about 500 amps at 48V (momentary).

    This well pump can bring the LP genset to its knees if there's much other load on the system.

    I believe the correct thing to do would be to replace the well pump with a three phase model that can soft start via a VFD style controller, but cost and time prevent me from going that route. I don't believe that changing the power system substantially is a good idea as 1) it's impractical and 2) it's more than adequate for everything else.

    I guess I've just addressed my own question, but if anyone else has more insight I'm all ears.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Capacitor for my Dishwasher?

    The extra strain of the Voltage drop on pump power-up isn't doing the pump any good either.
    You might think changing the water pump is the best solution. But a 400' well is quite a lift. That's probably a 2 HP unit down there. Right now you've got a 4 kW inverter supplying 6 kW to start the pump. No wonder there's trouble!

    So upping the inverter is the likely change, but that's $3000 as you know. You certainly could buy a dishwasher for less than that!

    You can put several smaller pressure tanks together, if you have room, but there again ... $$$ and you'd need enough capacity to cover the dishwasher's use without running the pump.

    Pumps are expensive too, darn it!
  • audredger
    audredger Solar Expert Posts: 272 ✭✭
    Re: Capacitor for my Dishwasher?

    Might I recommend an elevated storage tank to gravity feed your water? May need an additional pump to overcome the extra head but, you could then pump in the daylight when your loads were at a minimum. Might be able to downsize the battery bank requirements too.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Capacitor for my Dishwasher?

    By a second (or even a third) pressure tank. Pump all your water during daylight, (and maybe even do dishes during the day too) A pressure tank can be installed nearly anywhere in the line (within reason) and will (assuming similar size tanks) double your water capacity.

    The cost of another tank, and a bit of plumbing will probably be cheaper than additional PV or batteries. I would also look at the heat strip in the dish washer. The heater is a huge wattage draw in a dishwasher, and IMHO unneeded. The first is to super heat the water (turn up your gas if you need to) the second is dry the dishes. Let them air dry.

    Good luck,

    Tony,


    PS I was going to suggest doing the dishes by hand,,but I guess that is a non starter.
  • chevenstein
    chevenstein Solar Expert Posts: 100 ✭✭
    Re: Capacitor for my Dishwasher?

    I'd considered adding a tank (or two) and may end up doing so, but yesterday I solved this problem: I found a used dishwasher in good shape with mechanical controls and swapped it in. So far so good!
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Capacitor for my Dishwasher?
    I'd considered adding a tank (or two) and may end up doing so, but yesterday I solved this problem: I found a used dishwasher in good shape with mechanical controls and swapped it in. So far so good!

    Ah, the cheapest solutions are always the best solutions! :p
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Capacitor for my Dishwasher?

    Other problem with simply adding a cap, is the power source, will not be able to recharge it quickly enough. The extra load could eventually cause rectifier diodes to fail.
    But a replacement dishwasher is a good cure. Hope it's a energy saver.

    Still does not solve problem of overloaded inverter, which will die eventually.
    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 ,

  • chevenstein
    chevenstein Solar Expert Posts: 100 ✭✭
    Re: Capacitor for my Dishwasher?
    mike90045 wrote: »
    Other problem with simply adding a cap, is the power source, will not be able to recharge it quickly enough. The extra load could eventually cause rectifier diodes to fail.
    But a replacement dishwasher is a good cure. Hope it's a energy saver.

    Still does not solve problem of overloaded inverter, which will die eventually.

    The replacement DW uses about 1/4 KWH less for a cycle than the old one, time will tell if it works as well.

    On the inverter, the MS4448AE is rated for 6KW (real) power output for thirty seconds and 8.5 KW for five seconds, why do you think the inverter will fail? The line to line and line to neutral 100 millisecond surge ratings are also quite high (which is why I chose this inverter). If anything, I would think I'd chew the batteries up.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Capacitor for my Dishwasher?
    The replacement DW uses about 1/4 KWH less for a cycle than the old one, time will tell if it works as well.

    On the inverter, the MS4448AE is rated for 6KW (real) power output for thirty seconds and 8.5 KW for five seconds, why do you think the inverter will fail? The line to line and line to neutral 100 millisecond surge ratings are also quite high (which is why I chose this inverter). If anything, I would think I'd chew the batteries up.

    I think he's referring to the repeated over-loading of what is really a 4kW inverter every time the water pump starts - what was causing all the problem in the first place. Since the AC was dipping enough to shut down the dishwasher, that's quite a Voltage drop (outside of normal operating range). A definite overload. Inevitably this will shorten the inverter's lifespan, although by how much is impossible to predict. Not good for the pump motor either.

    But when the inverter fails you can replace it with a 6 kW unit and all the problems will go away. No sense shelling out the $ before then.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Capacitor for my Dishwasher?

    You may need to get a fast meter or oscilloscope on the battery bank and wiring too... I wonder if the inverter AC output droop is possibly the result of a drooping 48 volt battery bank?

    To run that large of inverter and its surges, you probably need 400-600 Amp*Hour bank (and cabling to support those large surge currents) to supply those peak currents.

    Plunging DC Bank voltage will also cause an increase in DC surge current requirements too (P=I*V; less voltage, more current, more drop, more current, more wear and tear on the inverter electronics).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Capacitor for my Dishwasher?

    This well pump can bring the 7KW LP genset to its knees if there's much other load on the system.

    I believe the correct thing to do would be to replace the well pump with a three phase model that can soft start via a VFD style controller, but cost and time prevent me from going that route. I don't believe that changing the power system substantially is a good idea as 1) it's impractical and 2) it's more than adequate for everything else.

    I think a new motor $500 (on your old pump) and VFD controller ($200) is a lot less than your inverter dieing, and waiting a week for a replacement.
    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 ,

  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    Re: Capacitor for my Dishwasher?

    I had a problem similar to this but of higher order. My central air conditioner has a very high starting current.

    I won't go into all details but my solution was a separate inverter solely for the air conditioner.

    I run both inverters from the same battery array. You may also have an issue with battery voltage slump which must be addressed with a sufficient battery, capable of the surge current.

    There are other damaging issues with A.C. voltage slump on motors. In my case, the separate inverter capable of the needed startup surge prevented the regular inverter from slumping voltage on the refridgerator and rest of house which could be damaging.

    I played with soft starter but the result was I able able to cut the surge peak amps down but it just extended the time of the startup surge.

    You should check your battery voltage slump first. A larger battery or high current AGM type to reduce the battery voltage slump may also reduce the time the water pump takes to startup by allowing your inverter to maintain its output voltage closer to normal. Also take a look at your AC wiring, with pump getting it own direct feed with sufficient wire gauge.

    Remember the more the pump AC voltage slumps, the longer the startup surge will last.
  • chevenstein
    chevenstein Solar Expert Posts: 100 ✭✭
    Re: Capacitor for my Dishwasher?

    I had forgotten about the droop on the DC side (and associated skyrocketing amperage....d'oh!). I anticipated large DC amperages so the battery cabling is short (~6 feet) and thick (two-aught), but the training battery bank is definitely too small. The inverter's manual even strongly discourages the use of large AC loads on smaller (< 400AH) battery banks, I knew this, but I did not want to destroy expensive batteries by accident. Running the voltage is down around 48VDC; I have no idea how low it goes for those first few starting cycles.

    OK, so I had been wanting to avoid pulling the well pump (and associated 400' of plastic pipe and cable) but I think that is where this is going. Though the twin inverter idea is intriguing I think the real problem is the pig I have for a pump and that is where I should start. I am a giant pack rat and have several capacitor start well pumps (deep and shallow) "in stock", but none large enough for 400' of head. That said, I've measured the water about 20' from the top of the well casing, so normally the pump is lifting maybe 20-50' of head. I could drop a 1/2hp capacitor start pump down there and solve the problem most of the time, but I'd likely kill the pump or not have water if the water level were to drop below 200'.

    If I had the money I'd put a three phase motor on the existing pump and get a single phase input, 3ph output VFD on it, or I could spend less and go the lots of above ground capacity/pump on the generator route but everything else in the house is so simple and works so well as it is. I had considered wiring the well pressure switch into the generator so that the generator would start and close a relay to run the pump but that's very much against our goals with this home.

    Hmmm...I'll update this thread when I decide on a change - thank you all for your insight, I really appreciate it!
  • lorelec
    lorelec Solar Expert Posts: 200 ✭✭
    Re: Capacitor for my Dishwasher?

    Have you considered using your generator to power your well pump? If you have enough elevation on your property, you could install gravity-feed storage tanks and fill them maybe once a week, give/take. A less elegant solution than using batteries and inverter, but probably a lot less expensive than upgrading those!

    Marc