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Justin avatar image

MPPT Load output switches off

Hi There

I have an issue on my SmartSolar MPPT 75/15 Charger controller, When the controller is in the "Float" state , The national luna DC fridge i have connected to the load output on the controller seems to "trip" and then comes back on and the fridge will run , Then when the compressor turns off and then back on again the same happens again and again while in the " Float" State.

But when the solar charger is charging the Battery in " Bulk" or "Adsorption" states the fridge runs no problem , The compressors can start and stop all day with no Issues , The issue only arises when the system is in the " Float" stage.


Why does it only happen when the charger is in the "Float" state ?

I Bought the SmartSoalar 75/15 Controller so i could track my consumption and Solar output.

but now seems i have wasted my money on this controller if i cant run my fridge on it . I need the solar controller to manage the load to make sure the fridge doesn't drain the battery to far during the evening


Install Detail

2 x 100 Watt Solar panels in Parallel

1 x 105 AH Royal 1150K Battery

1 x National Luna fridge / Freezer

SmartSolar MPPT Charge Controller


MPPT - Solar Charge Controller
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15 Answers
AndrewF avatar image
AndrewF answered ·

Hey there.

Just wanted to chime in and say I was having what sounds like a similar problem with my 75/15 when trying to run a fridge on a recent camping trip.

Of course, the fridge runs fine off the battery directly but I kind of wanted to utilise the battery saving tech of the load output, not to mention get an accurate meaure of how much power i used relative to how much I had been generating with the panels.

Sounds like it's a limitation of the hardware, which is disappointing but if that's the case, so be it.

Cheers

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Shiva avatar image
Shiva answered ·
I suspect the cause. I have the same problem. My roof fan MaxxFan automatically switched off when it is a sunny hot day. Exactly if you want the fan to work. On such a warm sunny day, I completely monitored it once and saw that my Votronic info panel switched on again when my fridge started. The power was interrupted for a short moment. The roof fan connected directly to the battery and that solved the problem of the roof fan. The peculiar thing is that power interruptions only occur on sunny days. In my opinion, this means that the MPT 75/15 adds up all the amperes, both the incoming and the outgoing. On a sunny day with my 2x 110 watt solar panels I am already over 10 ampere and then a starting fridge of 4.5 ampere can no longer reach it.
The mppt reduces the number of amps depending on how the battery is charged. You probably have to measure the full capacity of the solar panels of that moment (without the reduction of the MPP). The specified 15 ampere consumption current is, I think, not separate from the charging current. If these are counted together, you will soon be over 15 ampere.
I find this information from Victron misleading because I assumed that the capacity is 15 ampere charging current as well as 15 ampere consumption current.
Very disappointing because the more solar energy there is, the fewer devices I can switch on. It sometimes happens that the refrigerator no longer works.
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Richard avatar image
Richard answered ·

I am not technical but wondered if the config was 24v would this reduce the amps demand on the load and reduce the likelihood of it cutting out?

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Justin avatar image
Justin answered ·

@WKirby


I finally got my NTC's , I will be trying it on the weekend , I will keep you updated on the results.

Holding thumbs it works ,





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@WKirby

My experience with the NTC is still limited but the fridge does have trouble starting sometimes even with the NTC in circuit when voltage is low, (seems to start after 3 or 4 tries). A large capacitor after the NTC may be the best answer. I am going to try a 16 volt lithium Ion battery to provide the start current for the fridge. The battery won't overcharge but should have enough charge for the job. This is currently working on a DC-DC charger running a similar fridge.

randy_h avatar image randy_h ray_pridham@bigpond.com ·

Thanks for the followup Ray.

ray_pridham@bigpond.com avatar image
ray_pridham@bigpond.com answered ·

My 0.5 ohm NTC's have arrived and first tests suggest 1 x NTC works very well. Voltage drop at approx 3 amps is around 1 volt and the fridge starts without error with the fridges low battery value set at 10.1v.

The best news is the 100/20 doesn't cut the load off but starts the fridge in all modes including float. The NTC temp settles at about 75 deg C .

More testing on a road trip over the next few days, but for now a big thank you to Warwick and all who chipped in.

BTW something I read along the way said 2 NTC's in parallel probably won't work, one would heat first and carry all the load.

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WKirby avatar image
WKirby answered ·

I got the NTC which I ordered.
I have connected it up in series with the load which consists of both 55W filaments of a H4 car lamp. Remember, just one filament is enough to trip the Load Output.

The NTC does its job and starts both filaments without any problem.
The inrush current is limited to about 18A which is quite reasonable.

The possible downside is the heat that comes off the NTC. It is a resistor after all, so depending upon how much current is going through it, it might get hot.
It got up to about 85°C with a continuous 9A load.
It gets up to about 40°C with a 4.5A load.

I'm pretty certain that this will solve the fridge startup problem.
The thermistor is an Epcos B57127P0508M301 - 0.5Ω @25°C
If you are in SA then you could get it from RS Components. https://za.rs-online.com/web/c/passive-components/variable-resistors/thermistors/?searchTerm=B57127P0508M301

I hope it works with a fridge. I don't have one to test with, so hopefully someone is willing to try.

@Justin @ray_pridham@bigpond.com @Guy Stewart (Victron Energy Staff)


ntc-test.jpg (3.5 MiB)
scope-21.jpg (44.1 KiB)
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Thanks wkirby,


That looks very good. Apart from any heat generated, which in itself means lost energy, not good in a solar powered camp, there is also the problem of voltage drop. If I'm calculating right that could be about 2 volts meaning the fridge would stop with a low voltage error. Minimum voltage allowed is 10.1 before it gives an error and stops.

How about a slightly lower resistance NTC, would the regulator cope?

BTW; I found a 9 ohm NTC, it gets very hot very quickly :)

WKirby avatar image WKirby ♦♦ ray_pridham@bigpond.com ·

I didn't find anything less than 0.5Ω. You could probably put 2 in parallel to get 0.25Ω , but that might be too low.
At 5A, you are probably dropping about 5W.
The only other way is to have some sort of transfer relay which allows the load to start directly from the battery, but then switches over after a second or two.

Hi Warwick


Where did you order the NTCs?

Mine came from Element14 (Maybe called Farnell elsewhere). See Wkirby's supplier above.


Ray

Boekel avatar image
Boekel answered ·

One option:

connect a relay between battery and loads, drive the relay coil through the load-output of the MPPT. Don't forget to put a diode over the relay-coil (some relays have this build in)

Don't forget to fuse according to wire-size and relay current - and please choose a relay a couple of sizes bigger than maximum current you expect. 70A automotive relays are cheap and good, but make sure you have a spare on board.

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I think you may have missed the point somewhere in this long thread :)
The relay of course is an option that has been suggested, but people want to power their load from the Load Output terminal directly because it is metered. If they drive a relay, then they will not see the consumption of their loads. This feature is one of the driving factors for them to buy a Victron MPPT over any other.

My apologies, didn't know about the metered part.
I also have only worked with MPPT's without the load output.

Justin avatar image
Justin answered ·

@ray_pridham@bigpond.com

@Guy Stewart (Victron Energy Staff)


Hi Ray_pridham

That is exactly the same issue i have also seen with my Fridge . My battery was also near full charge or fully Charged i even had it on a Battery charger the night before to make sure it was 100 % fully charged . I get the issue with the Compressor not starting the first time in Float


So the fridge Compressor will start , It will stop for a Second and then it i will start and work okay until the fridge stops the compressor again


So My question if in rush current was an issue the fridge would then never Start ??

And then why does the fridge start a second latter , Surly there would be two inrush currents then ??


I will try upload a video of the fridge and how the Compressor starts up, then switches Off , then starts up and runs okay .

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When the MPPT Load Output shuts off, it tries again a second or two later.
Now, with a compressor you not only have the inrush current of the electric motor, but also the initial pressure if the refrigerant gas as the system has stagnated since the previous cycle.

I have a NTC ICL (Inrush Current Limiting) thermistor which I am going to test tomorrow. I think it will be the answer. I'll update on how well it works in my tests.

I bought this one: https://za.rs-online.com/web/p/thermistors/1218214

@WKirby


Thanks for the effort !!! , I was also reading about those NTC ICL . Please let me know how your testing goes , It would we really awesome to run the fridge off the Victron controller so i can see my consumption etc..


Guy Stewart (Victron Community Manager) avatar image
Guy Stewart (Victron Community Manager) answered ·

If the fridge requires 280W to start, and the batteries are nice and full, the voltage will be high 14V, requiring 20A.

If the weather has been bad and the batteries are not charged, getting low at 12.2V you will require 23A to make the 280W required.

That additional 3A current may be all the difference necessary.


With fast test equipment, you may see the battery voltage dip even lower during high current draw (this will not happen if the solar is also powering the load keeping voltage high). The lower the voltage, the higher the current required for the same power demand and the higher likelihood of overload.

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Interesting, my first test was on a dull day and my 4.5amp lamp was only switched off when the charger reached float mode, so does this mean the extra voltage available in bulk and absorb allowed the lamp to start and run?

My later test with a 1.9amp lamp and 4.5amp halogen lamp was on a sunny day and the small lamp worked fine and the 4.5 lamp basically would not work at all. Both times batteries were near full charge.

Justin avatar image
Justin answered ·

@Guy Stewart (Victron Energy Staff)

The strange thing , Maybe everyone is missing the point here

When the solar charger is been charged , Either in the " Bulk" or ' Abortion" and there is for example 6 Amps power been created by the solar system the fridge works Perfectly , No issues , It runs all day , Multiple compressors restarts , i can even bypass motor speed control and run fridge at maximum speed. The controller is then able to handle the inrush currents perfectly all day.


The issue only really comes up when there is very little to no power been Generated from the solar panels , this can be in "Bulk" or " Float" the problem is even worse in "Float" when the solar energy been created is very little to "Float" the battery .

This proves to me that the inrush current is not the issue , if inrush was an issue it would do it all the time , Regardless of how much solar energy is been created .


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Guy Stewart (Victron Community Manager) avatar image
Guy Stewart (Victron Community Manager) answered ·

It is a surprise to me that either of the units load output is able to run a fridge compressor. That is typically a very high current load.

The load terminal on those units is a great and low cost convenience, but it is very limited by design.

The robust, reliable and accurate solution is a BMV, and MPPT connected to a CCGX.

This is a lot more expense, probably more than you want to spend and in someways not as good (as the VictronConnect app makes everything very handy). But your application falls just on the line, too big for that little MPPT to be 100% and too small to justify full system.

I hope it doesn’t sour you on Victron as a whole though. One of the big strengths is a product range that spans tiny applications to massive power demands.


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Justin avatar image
Justin answered ·

@WKirby

I managed to get hold of a second Victron 75/15 Mppt controller and ran the exact same tests.

This second controller seems to be better . It only drops the load after every 4 to 5 compressors start ups.

How can the second controller , same Hardware / same firmware etc on it perform much better ? My Unit drops the load almost every time the compressor starts up

I have Bought and invested in Multiple Victron Equipment and looking at more , from this i don't know if i want to continue with Victron any more , this is an issue that needs to get resolved as i bought this controller to be able to see my Solar consumption vs Solar generation and i don't feel running my fridge directly off the battery is the correct way as i wont be able to use the controller for what i bought it for. I am going on a 21 day road trip so i need to be able to monitor my solar system is creating enough energy .


Please can you assist in getting some sort of answer to my problem , And as you have seen i am not the only one with this issue .


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You have to understand that the load Peak hard on the limitation is hard to handle an may differ a little bit from device to device. The load output of an electronic controlled output is much more sensible than a simple normal fuse. It have advantages in case of no dameged fuse in case of error, but has dissadvatage of beeing much more sensitve to starting peaks. So if you want to handel bigger loads which cause problems on the small load output simple take an additional BatterieProtect 65A. Thats made for that, and thats the way our customers handle such loads.

Since I have performed some tests on the Load Output, I have a much better understanding how and why it does this. I have posted my findings over here: https://community.victronenergy.com/questions/1861/smartsolar-10020-load-switches-off-in-float-mode.html

I discovered that there isn't a problem with the MPPT. To protect it's self, it responds very quickly to over current events that certain loads present.

I want to test, but I think an NTC inline with the Load Output will "soften" the inrush current. It's something outside of the MPPT, but it should solve your problem.

Justin avatar image
Justin answered ·

HI Wkirby

Thanks for getting back to me, I am glad i am not the only one with the issue now .

I have also noticed that my controller is doing the same in "Bulk Mode" when there is very little solar energy or Amps been generated from Solar .

I also measured the inrush Current on the fridge and it never seems to go above 6.02 Amps

Screen shot is of the controller later in the afternoon when the fridge restarted . " Very little" energy been created .


I am even more convinced this is a software / Programming issue on the controller




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WKirby avatar image
WKirby answered ·

Ja, so those algorithms pertain to the battery voltage sagging due to inrush currents, and will allow the low voltage condition to be present for 2 minutes before disconnecting the load.
You are not experiencing this, I think you are experiencing the MPPT load output being current limited at 15A and this does not have a time condition. The fridge wants more than 15A to start when battery voltages are at FLOAT voltage or less.
Although I don't know the circuit designs for MPPT or PWM, I'm sure they are different and I'm sure the MPPT responds to over current events quicker than the PWM does.

If I am right in my thinking, then the inrush current of the fridge must be only just above 15A because, like you said, you do not seem to have a problem when battery voltages are at the high end.
I'm sorry, I don't really have any more ideas for you. Hopefully someone else can chip in and maybe prove me wrong.

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What i will do is let the fridge run on battery and measure the amps / Load when the compressor starts up and get back to you . The fridge Dc input has a 15 Amp Fuse , So doubt the load of the compressor will use more then 15 amps on start up otherwise i would need to replace the fuse every time the compressor starts up ?

I may have been barking up the wrong tree here. It seems someone else is having a similar problem to you. I am now more convinced that you fridge has nothing to do with this. I need to think some more.

https://community.victronenergy.com/questions/1861/smartsolar-10020-load-switches-off-in-float-mode.html?childToView=1877#comment-1877


You'll also notice from the thread I linked to above that mvader is going to get R&D to investigate this, so hopefully they'll reach a resolution soon.

WKirby avatar image
WKirby answered ·

It is important to remember that the LOAD terminals on the MPPT have a maximum rating of 15A. A fridge compressor can briefly have a high startup current initially.
Now, when the MPPT is in BULK / ABSORB, the battery voltage is higher than when it is in FLOAT. I am not entirely sure how the National Luna fridges work, but I did read that they have a wide input voltage range which suggests to me that they have a DC/DC converter within. I have discovered that the National Luna fridge uses a Danfoss BD35 DC compressor. This means that the fridge's brief inrush or startup current will be higher at lower battery voltage (FLOAT) than when the battery voltage is high (BULK or ABSORB). The BD35 compressor has maximum running current of 6.5A (I don't know what speed the motor is set to run at). If the inrush current, which could well exceed 15A. is being limited (to 15A) then it may well cause the symptoms that you describe. Do you get any error code flashing LED on the fridge?

Another thing unrelated to the MPPT its self is the size of the cable going to the fridge. The National Luna manual (and the BD35 datasheet) goes into some detail to ensure that your cable is correctly sized according to its length.
I should add that the size requirements for the cable between the MPPT and the battery will need to be included as it forms part of the circuit to the fridge.

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Hi There

Thanks for getting back to me so soon!


I am using the Cable that comes with the fridge for the DC Supply , as specified by National Luna and is only 1.5 Meters long ( Its 6mm cable)


The only thing is , I have tested this on my Older PWM 10Amp solar controller , and no problems at all , Fridge works 100% with no Issues. All the same cables , Only different solar controller type

I read there is a User defined output Algorithm , and that some have a 2 minute delay to help with the Inrush current , Attached is a picture from the Manual , Think it could Help ??



inrush.jpg (76.5 KiB)