I’m looking into a lot of people their small off grid solar setups.
Regarding the position of the circuit breakers they use between the MPPT charge controller and the battery, They all put the MPPT on the source(batt) side of the breaker, and the Battery on the load side.
Is this the correct position of a DC breaker?
Below I found a thread here of someone asking a similar question and the answer was the complete opposite.
I know it’s better to use a fuse, but, If you would use a breaker, what would be the correct source and load for the connection between the MPPT and the battery?
If you are only ever going to charge the battery from the MPPT then the MPPT connects to source/ battery side and battery to the load side.
If you are also going to discharge the battery through the MPPT load terminals then it does not matter as one way will be wrong.
BTW, if you use a breaker, use a good one like BlueSea (avoid the fakes) and do not use the cheap ebay / amazon ones there are many people who report poor behaviour.
Thanks,
I won’t be using the load terminals of mppt but will use the inverter for that.
So basically only 2 connections from/to battery:
MPPT
BATTERY
As the mppt also uses battery for its power
The argument in the answer of the linked thread is that the battery is the “highest” potential and therefore needs to be connected to the battery / source side of the breaker.
It sounds logical and that the breaker in between the mppt and battery is more likely to receive a short from the battery..
I see a lot of similar RV and boat- solar setups and they all have it like you just said.
I’m planning to order BlueSea breakers 80 and 25.
So to verify, the answer from the linked thread / video above is wrong (in this case), right?
Thanks,
I won’t be using the load the terminals of mppt but will use the inverter for that.
So basically only 2 connections from/to battery:
MPPT
BATTERY
As the mppt also uses battery for its power, isn’t the battery the “highest” source and therefore needs to be connected to the battery side of the breaker?
Isn’t the breaker in between the mppt and battery not more likely to receive a short from the battery? Which seems logical and the argument of the reply in the thread I linked above.
I see a lot of similar RV and boat- solar setups and they all have it like you said.
I’m planning to order BlueSea breakers 80 and 25.
So basically the answer from the linked thread is/ video is wrong, right?
| pwfarnell Victron Expert 15 May |
| - |
If you are only ever going to charge the battery from the MPPT then the MPPT connects to source/ battery side and battery to the load side.
If you are also going to discharge the battery through the MPPT load terminals then it does not matter as one way will be wrong.
BTW, if you use a breaker, use a good one like BlueSea (avoid the fakes) and do not use the cheap ebay / amazon ones there are many people who report poor behaviour.
Interesting now that you have mentioned the short circuit, because a short between the solar controller and the battery would need the arc breaking with the battery as a source, so that is a good argument that I am wrong in the post above and the linked answer is correct. This means the breaker should be next to the battery to protect the wires, not by the MPPT. The MPPT is a fixed current source and the wires should be larger than the max current anyway.
Yes that makes more sense to me too.
The mppt (100/20) has a 25A fuse itself. The battery a 100A fuse so, it’s indeed more logical to put the 25A breaker between mppt and bat. with the battery as the source side.
Just a double protection because probably the 25A fuse of mppt will blow before the breaker, but anyway. Better safe than sorry.
The strange thing is though, that when you look at the breakers in other people’s setups, they almost all have it the MPPT on the source/batt side and the Battery on load.
Hard to believe that almost everyone has it wrong, but could be..
What voltage are we talking about here? Anything close to or above 60V requires special attention.
For the PV wires you should use 10x38mm gPV fuses (IEC 60269-6). Not a breaker. For class 5 and class 6 wires you also must use a ferrule.
For the batterij side you must use bi-directional breakers that comply with IEC 60269-6 (I need to check this as I am having a brain fart after an insane long week).
I don’t know where you are located, but that, in case of a fire, will become priceless. You insurer will look at the installation and will use anything against you to deny a claim.
Thanks for that info!
It’s a small 12v portable emergency backup power system with 100ah lifepo4 battery, 12/800 inverter and 100/20 mppt. And a 200w foldable suitcase panel.
The 12/800 victron inverter has a bolt on 150a 32v MIDI fuse. (Built in but replaceable)
The positive battery cable (25mm copper) will get a bolt on MEGA 125A fuse connected to the battery nut.
In between them, 25cm away from the bat., I’ll put a 100ah BlueSea breaker with battery as source.
The Dokio suitcase has its pv cables XT60. Connected to the 100/20 mppt.
From there I have the recommended 6mm cable to the battery.
I was planning to put a 25 or 30a BlueSea breaker in between the battery and the the mppt.
The initial question was which side should be the source and load.
So following the thread linked above I was planning to put the battery on source.
The breakers are extra as all devices have the proper fuses. And it gives the option to disconnect them too.
It’s a DIY project to provide mobile and/or emergency power when needed.
Sounds like a fun project. But hold on. Dokio? That’s only 18 Volts. Scrap everything in between the panel en charger. Except for the solar panel wiring of course
No. Seriously. You’ll be fighting resistance. You don’t want to add a ‘3 Watt heating element’ like a breaker and/or fuse holders. Those foldable panels are already struggling to perform anyway.
Now. About that 100/20 MPPT. My two cent. Massive overkill. I don’t even know if that is going to work for such a low voltage.
Listen. I know. Sounds negative. Not really my thing, but you’ve got to be realistic. Right?
Yes quite fun project to learn about ohm’s law and build a small portable backup power station myself.
It’s a really interesting field.
There is nothing but the cabling between the panel and the charger. The breaker I was planning to put in between the battery and the MPPT.
Would you also suggest to take that one 25A out?
The Dokio came with a lesser pwm charge controller.
If the 100/20 smartsolar doesn’t get enough juice from this panel, I will keep using the pwm for now.
Then I will just keep the 100/20 for possible future upgrade so I can always connect 2 big regular panels to it.
Yes. I would certainly skip the breaker, with the 18Volt panel. You may want it with more powerful panels. Please keep that in mind. It all depends on what you do / use.
| 