voltage drop under load

kearly · July 2012

We recently had a battery (48volt, 41KWH) based PV system installed - we love it! There is one thing that worries us though: when the refridgerator OR toaster oven turns on, the lights dim and our fan slows for a couple of seconds. We're not approaching a full load on the inverter (Magnum 4.4KW) since the total load at the time the fridge or oven turns on is only around 250 watts and the refridgerator surge is around 1100 watts (toaster oven is around 1350). We've looked at the inverter and the voltage is dropping to between 109 and 114.

- is this normal on a battery system or could something be wrong with the inverter?
- is this a problem for electronics or appliances?

Thanks for your input.

BB. · July 2012

Re: voltage drop under load

What is the battery voltage at the input to the inverter when you have the dimming?

And what is the output voltage at the inverter? (is there voltage drop in the AC wiring from the inverter to the loads?)

-Bill

Cariboocoot · July 2012

Re: voltage drop under load

Welcome to the forum.

No, this is not normal. Especially not on a 48 Volt system.
The first thing to check is the DC side of the inverter: what size is the battery bank and what gauge and length wire is used to connect it to the inverter? Then you need to monitor the DC Voltage when one of the AC Voltage drops occurs, to see if it is a strain on the batteries causing it.
The second thing to check is the AC wiring. Most Magnum 4kW inverters put out 240 VAC normally, and this should be "split" at the breaker box with the center "neutral" output connected to Earth ground. If that isn't done the line Voltage on either "side" can waiver considerably depending on the loads.

inetdog · July 2012

Re: voltage drop under load

kearly wrote: »

We recently had a battery (48volt, 41KWH) based PV system installed - we love it! There is one thing that worries us though: when the refridgerator OR toaster oven turns on, the lights dim and our fan slows for a couple of seconds. We're not approaching a full load on the inverter (Magnum 4.4KW) since the total load at the time the fridge or oven turns on is only around 250 watts and the refridgerator surge is around 1100 watts (toaster oven is around 1350). We've looked at the inverter and the voltage is dropping to between 109 and 114.

- is this normal on a battery system or could something be wrong with the inverter?
- is this a problem for electronics or appliances?

Thanks for your input.

1. How did you determine that the surge on your refrigerator was 1100 watts? If your measurement of the surge is not catching the full peak value, then that might explain the dip. What is the running power consumption of the fridge?
2. How was the value of 1350 watts for the toaster oven measured? A resistance heating element that normally runs red-hot may have a lower resistance when cold which could cause a surge for it too. But not by as large a factor as for a motor load. A Kill-a-Watt meter should show a power surge for the toaster oven if there is one, but it might miss some of the peak surge for the fridge.
3. Are you using 120 volt appliances with a 240 volt inverter output, center neutral? If so, are the fan and lights on the same phase as the fridge and toaster oven? Or are you using a full 240 volt system with 240 volt appliances?
4. If the voltage at the inverter dips and then recovers, in time with the lights and fan, then the inverter output definitely is not regulating properly for some reason. Wiring resistance should not make that kind of difference unless the duration of a power surge to the fridge or toaster matches the voltage dip. Can you tell whether the voltage at the inverter returns to the same value as originally after the surge or just comes partway back up and you cannot tell the difference from the fan and lights? That would add to the suspicion of wiring resistance problems on either the DC or AC side.

vtmaps · July 2012

Re: voltage drop under load

kearly wrote: »

We recently had a battery (48volt, 41KWH) based PV system installed - we love it!

You have gotten some good advice here. If you do not have the test equip that you need to follow that advice, call your installer. The system is definitely not working right. A reputable installer will make it right. --vtMaps

icarus · July 2012

Re: voltage drop under load

All that said, to some extent it depends on the total size of the battery bank. 1300 watt load plus the fridge, say 1500 watt is ~31 amps on a 48 vdc system. How big is the battery,a ns how low does the battery drop when running the toaster and the fridge?
Also, the starting currrent of the fridge may be very much higher than the 1100 watts for a bit as it starts! Depending on design.

Tony

mike95490 · July 2012

Re: voltage drop under load

kearly wrote: »

We recently had a battery (48volt, 41KWH) based PV system installed - we love it! There is one thing that worries us though: when the refridgerator OR toaster oven turns on, the lights dim and our fan slows for a couple of seconds. We're not approaching a full load on the inverter (Magnum 4.4KW) since the total load at the time the fridge or oven turns on is only around 250 watts and the refridgerator surge is around 1100 watts (toaster oven is around 1350). We've looked at the inverter and the voltage is dropping to between 109 and 114.

- is this normal on a battery system or could something be wrong with the inverter?
- is this a problem for electronics or appliances?

Thanks for your input.

Not normal. I have about 200' runs from inverter to house loads, and about 60' from inverter to shop. With right size wires, it has no dimming, even with starting saws or the welder.

When the TOASTER comes on, does the inverter recover the voltage while the toaster is running, or does it stay dim/low voltage till the toaster cuts out?

inetdog · July 2012

Re: voltage drop under load

vtmaps wrote: »

You have gotten some good advice here. If you do not have the test equip that you need to follow that advice, call your installer. The system is definitely not working right. A reputable installer will make it right. --vtMaps

One last logical test you can perform without any test equipment at all:

1. Use the toaster oven because it is more controllable and should have less surge.
2. Turn on the toaster, wait for the dip in light brightness to end, then wait maybe a minute more.
3. Now watch the lights as you turn the toaster off.
a. Do they get brighter and then dim again?
b. Do they get a littler brighter and then stay that way?
c. Do they not change at all?
The first result will tell you that the inverter is not be regulating properly. The second result will tell you that you probably have a high resistance/voltage drop problem somewhere along the way. The third result will tell you that my logical approach has failed.... :-)

kearly · July 2012

Re: voltage drop under load

I'll try to answer as many of the questions as I can but some I'm not sure about:

- the battery is reading 50.5 volts, when we turn on the toaster oven it drops to about 49.9.
- we tested the wattage on toaster oven and refridgerator with a kill a watt type device (different brand)
- when we tried the test inetdog recommended, the lights did a slight flicker when we turned off the oven too (same as when we turned on). With the fan (which is easier to monitor than the lights), when the toaster oven turns on it slows down and then gradually speeds back up to normal over about 10 seconds. There is no noticable difference in fan speed when we turn the toaster oven off after a minute.
- the wire length between the battery bank and the inverter is about 16 inches, can't tell the wire size
- we aren't using any 240 volt appliances on the inverter, it is only supplying 120 loads

One other thing, it does this same thing even during the day when the battery is charging. If I understand it right, the controller is taking the power from the PV panels then instead of the battery, which makes it seem like it isn't battery related. Is that right?

Our installer is very good and if there is definately something wrong, I'm sure he will try to fix it. He didn't think it was a problem when we noticed it the first day.

Thanks! Katherine
-

BB. · July 2012

Re: voltage drop under load

Asking to measure the voltage right at the DC input lugs to the inverter (sometimes the wires are too small or there is a poor connection somewhere--Although, with "heavy loads", you might be able to feel the wire/terminal getting hot).

Since you are hearing the motor slow down, does your Kill-a-Watt type device have a frequency readout? It almost sounds like the frequency is not stable with the inverter (odd-but possible I guess).

Also, if we cannot help you here, call the service number for Magnum--I have heard good things about their service folks.

By the way, when you measure ~50.x volts, what is happening with the system (during the day when recharging? Or at night and system is discharging--no AC backup genset power)? 50.x volts is low if charging, but probably about right for a well charged battery bank just being discharged in the evening.

-Bill

icarus · July 2012

Re: voltage drop under load

A cheap indirect read infrared thermometer is. Greet too for the tool chest of any PV system. Point it at crimped lugs, or breakers or other lugs can easily reveal a hot spot,

Not to hijack thread, but sins Bill noted looking for heat on lugs.

Toniy

Cariboocoot · July 2012

Re: voltage drop under load

50 Volts is low for a 48 Volt system. Normally we'd expect an at rest Voltage of 51, and a "running" Voltage (some charge coming from the panels) higher than that; preferably about 55.
So again we're back at determining the battery bank's capacity and what size wires it is connected with. If it is too small, DC Voltage will fluctuate too much under load demands and that can cause a parallel fluctuation in AC Voltage as the inverter struggles and fails to maintain output. We see this often with 12 Volt systems; not so much so on 48. I hope you haven't been stuck with some tiny 100 Amp hour battery bank.

mike95490 · July 2012

Re: voltage drop under load

kearly wrote: »

... Our installer is very good and if there is definately something wrong, I'm sure he will try to fix it. He didn't think it was a problem when we noticed it the first day. ....

Al I can say is your installer is very good - at making up a good story. No way should a proper system have the symptoms you describe.

SolaRevolution · July 2012

Re: voltage drop under load

Have you checked this while the generator is on?

If the problem goes away it is an inverter or DC side issue. If it still happens it is in the AC wiring.

-Alex

Photowhit · July 2012

Re: voltage drop under load

I'll throw my vote in for AC wiring, You say it has properly sized cable, but 200 feet, one way, with 12 gauge with an 11 amp load(1300watt/115V) would give you about a 6.5% voltage drop. 10 gauge would give you about a 4%, so somewhat close to what your seeing so if it's measuring the curcuit either size might give close to that drop.

The voltage drop on the battery side isn't bad, and the voltage should represent a battery NOT recieving input but only common household draws. My smaller 24V system normally shows about 25.1 or so when I come home 3-4 hurs after sunset, with the fridge running almost full time in the heat, when I kick on the AC it'll drop quite a bit (500watt window unit) lower in relationship to your 48V system. I can't recall exactly now, since I have the AC on timer now.

Your 41Kwh / 48V battery should be about 850AmpHour and weigh about 2200lbs? Noting your DC side voltage drop I think your DC side is fine.

EDIT; Sorry I missed that those where Mike's 200 foot runs, so what kind of distances are we looking at?

waynefromnscanada · July 2012

Re: voltage drop under load

And what wattage is in the mix with solar panels? And how much does the battery voltage drop when using the toaster oven on a sunny day?
This business of the fan slowing down, then slowly regaining it's speed when turning on the oven is a strange one. Yes, a cold element will draw more power than a red hot one, but not enough to cause that in a properly operating system. "slight flicker of the lights" is rather subjective though, as is the slowing of the fan. One person's "slight" may be something only just barely noticeable, while to another, it could mean rather substantial dimming or speed change. Having that fan plugged into a Kill-A-Watt and monitoring the voltage while turning the toaster on and off might reveal some clues.

petertearai · July 2012

Re: voltage drop under load

Hi. My system i don't notice any light flicker when the fridge starts. But if turning on the vacume at night there is momentary slight dimming of the lights.

BB. · July 2012

Re: voltage drop under load

Also, different lamps will behave differently to power fluctuations... Some CFL/Florescent ballasts will cause lamps to flicker more obviously vs filament lamps. I would guess some LED lamps "show flicker" more obviously than other brands/models.

Ballasts (CFL, florescent, LED type lamps), are an added expense, and mfg. will build them as cheap as possible--Which can either hide or make flickering from voltage fluctuations. A different brand may flicker less (or more) on the same circuit.

-Bill

kearly · July 2012

Re: voltage drop under load

- the 50.5 volts was at night when the battery was fully charged but not charging. It's higher during the day when charging.
- I just found in my notes the battery is 850 Amp Hours and yes, weighs something over 2000 lbs.
- we don't use a generator for backup, use the grid for backup and haven't done this experiment with it on (no net metering allowed here)

My installer is coming tomorrow to do some final things. I will get him to look at this now that I know it isn't normal. Thanks for all the input and I'll let you know when I find out what's wrong.

Katherine

icarus · July 2012

Re: voltage drop under load

That still soundsa bit low. Should be closer to 50.8 or even a bit higher if freshly charged.

T

Photowhit · July 2012

Re: voltage drop under load

kearly wrote: »

- we don't use a generator for backup, use the grid for backup and haven't done this experiment with it on (no net metering allowed here)

While there are no teeth, net metering is the law of the land. The no teeth part is no penalty. I live in a county with a backwards Coop and they have place lots of things in place to prevent people from doing 'grid tied' solar. ...but recently they have been relaxing their requirements. It appears that they only charge for a single 'user fee' now ($25) though you must have 2 meters. and they are doing 'net metering' at their cheapest retail rate(rates go down with usage here) rather than wanting to buy wholesale. Still they have a $25 user fee per month making it a near draw.

Might keep an eye on their future 'net metering' availability. I know, I will watch my local utility. I understand there are pressures, via federal regulation for companies to aquire a certain % of their wattage from renewable sources.

kearly · July 2012

Re: voltage drop under load

I told my installer I was concerned about the light flicker and fan speed change and he called Magnum technical assistance (from here so I heard the conversation). They said it is not abnormal and won't hurt anything. That the plus or minus 5% of 120 volts is the normal range but when a large load comes on voltage may momentarily drop. Guess I'll get used to it and hopefully it won't cause any problems with our fans and other appliances. Thanks for all the input.

Cariboocoot · July 2012

Re: voltage drop under load

5% on 120 Volts is 114 to 126. You were reporting Voltages below 114, weren't you? That's quite different.

vtmaps · July 2012

Re: voltage drop under load

I just reread this thread. Your 'problems' are, in fact, real problems. I wouldn't take "this is normal" for an answer.

I have been under the impression that yours was an off-grid battery system. On rereading I see that you do have grid. It makes me wonder exactly which model Magnum you have and how it is configured. Perhaps that is a clue that some Magnum experts (not me) can use to explain what's happening. --vtMaps

kearly · July 2012

Re: voltage drop under load

we are operating off grid but using the grid as backup in the same way others use a generator. The grid switch is off but can be (manually) turned on to bypass the inverter to supply loads when needed.

Cariboocoot, yes we see the voltage drop momentarily (on surge) to 109-114 but what they said is that it that the plus or minus is during normal operation and may go further off at surges.

voltage drop under load

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