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Amped up and confused!

Sundog33

Sundog33

Sun Bather
Joined
Feb 1, 2021
Messages
240
Location
Cinnaminson, NJ
SO, Ive had my new set up now for over a year. 200AH LifePo4 battery, Overkill BMS, Victron 100/20 and 200Watts of Solar in Parallel
running fine but wanted more solar to charge while I'm using power during the day.

I decided to add 2 more 100w panels and ran 4 in Series/Parallel to get 32v @ 12.4Amps and blew my 20Amp Battery breaker.
I then ran the 4 Panels in Series to get 64v @ 6.2Amps and blew my 20Amp Battery breaker.
I then removed 1 Panel and ran 3 Panels in Series to get to get 48v @ 6.2Amps and blew my 20Amp Battery breaker.

Then, I noticed that even though the Victron said I was getting the right amps (pictured @ 5.5amps)
my BMS was showing I was getting twice as many amps (pictured @ 11.27amps) This reading was not done in full sun, so it got higher and blew.

What am I doing wrong?? Why is the BMS doubling my amps?
 

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Panel voltage and amps going to your SCC is converted to battery voltage and amps based on wattage. Say you have 32v of solar at 12.4a. That is 396 watts into your SCC. Now at your battery 396 watts = battery charge voltage (I am guessing here 14v for 12v battery) X Amps solve = 28.3a Your breaker is overloaded.

No matter how you wire things W=VA
 
Mattb4 said:
Panel voltage and amps going to your SCC is converted to battery voltage and amps based on wattage. Say you have 32v of solar at 12.4a. That is 396 watts into your SCC. Now at your battery 396 watts = battery charge voltage (I am guessing here 14v for 12v battery) X Amps solve = 28.3a Your breaker is overloaded.

No matter how you wire things W=VA
Click to expand...
Thanks but don't fully understand? Is it my Breaker thats the problem here? Should I put a 50amp
Breaker? Is my Victron 100/20 effected by the Amps on the Battery?
 
I know this is a dinky system from what most here deal with. Just a 4 pack of LifePo4s. I just run floor fans and fish tanks, but I would think I could put more than 200watts of Solar into it and not blow it up? Maybe not?
 
You actually have several limitations. For one your Victron is a 20a unit. That means it only outputs 20 amps at battery voltage. If you are running 12v batteries 20a X 12v = 240w (Victron specs 290w)
See spec sheet here: https://www.victronenergy.com/uploa...-MPPT-75-10,-75-15,-100-15,-100-20_48V-EN.pdf

Than there is your 20a breaker limitation and finally there is the wire size limitation.

Your batteries may be a limitation on charge and discharge currents. Check the specs.
 
Sundog33 said:
SO, Ive had my new set up now for over a year. 200AH LifePo4 battery, Overkill BMS, Victron 100/20 and 200Watts of Solar in Parallel
running fine but wanted more solar to charge while I'm using power during the day.

I decided to add 2 more 100w panels and ran 4 in Series/Parallel to get 32v @ 12.4Amps and blew my 20Amp Battery breaker.
I then ran the 4 Panels in Series to get 64v @ 6.2Amps and blew my 20Amp Battery breaker.
I then removed 1 Panel and ran 3 Panels in Series to get to get 48v @ 6.2Amps and blew my 20Amp Battery breaker.

Then, I noticed that even though the Victron said I was getting the right amps (pictured @ 5.5amps)
my BMS was showing I was getting twice as many amps (pictured @ 11.27amps) This reading was not done in full sun, so it got higher and blew.

What am I doing wrong?? Why is the BMS doubling my amps?
Click to expand...
You had a 200w of solar at 12v battery with a 20A SCC and a 20A battery fuse prior to upgrading your solar array. As far I can tell that was fine because 200W / 12v = 16.6A going to your battery.


You've added another 200W od solar, which means at full Sun you are now with potential of 33.2a charging, limited to 20A charging by your SCC.

The fuse you decided to use before was only good for 20A, you've reached the fuse rating now. In my humble opinion, consider a bigger fuse.


The numbers I've used do not account for precision, rather standard numbers for easier understanding.

I'm sure someone will correct me if I'm wrong about this.
 
Mattb4 said:
You actually have several limitations. For one your Victron is a 20a unit. That means it only outputs 20 amps at battery voltage. If you are running 12v batteries 20a X 12v = 240w (Victron specs 290w)
Click to expand...
Watts are King. This is often even confusing to licensed electricians.
 
Sundog33 said:
I know this is a dinky system from what most here deal with. Just a 4 pack of LifePo4s. I just run floor fans and fish tanks, but I would think I could put more than 200watts of Solar into it and not blow it up? Maybe not?
Click to expand...

The issue isn't the controller. Your system is under designed.

100/20 means 100Voc max PV INPUT into the MPPT and 20A OUTPUT to the battery.

Your 400W array will NEVER put out more than 290W to the battery, 20A * 14.5V = 290W.

A 20A breaker on a circuit that handles 20A = popped breaker.

Breakers should be sized 1.25X the current to avoid nuisance trips.

Wire between the MPPT and battery should be 12awg or better.

The breakers you have selected appear to be extremely low quality. Surface mount littlefuse, blue sea, etc., brands are far superior and worth their price.
 
HighDesertOffgrid said:
Watts are King. This is often even confusing to licensed electricians.
Click to expand...
I probably harp too much on the Watts = Volts X Amps in the forum here.
Like all algebraic equations you can solve for the unknown by having the knowns.

If you know watts and you know volts you can calculate amps. W/V=A
If you know watts and you know amps you can calculate voltage W/A=V

If you do not know 2 variables you can not calculate the 3rd. Saying something is so many amps without giving you either a wattage or voltage creates an unsolvable equation.
 
Matt, Forgive me if I'm being rude but I already know the Watts = Volts X Amps because it tells me right on the Panels.
16.77Volts / 6.5Amps /100watts. I don't have to calculate anything or so I thought. Parallel doubles the Amps and Series doubles the Volts.

What I don't understand is what the relationship is between the Battery current and the Solar current. Why in this example is the solar current different than the Battery current?
 

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sunshine_eggo said:
The issue isn't the controller. Your system is under designed.

100/20 means 100Voc max PV INPUT into the MPPT and 20A OUTPUT to the battery.

Your 400W array will NEVER put out more than 290W to the battery, 20A * 14.5V = 290W.

A 20A breaker on a circuit that handles 20A = popped breaker.

Breakers should be sized 1.25X the current to avoid nuisance trips.

Wire between the MPPT and battery should be 12awg or better.

The breakers you have selected appear to be extremely low quality. Surface mount littlefuse, blue sea, etc., brands are far superior and worth their price.
Click to expand...
I agree. I never saw anything higher than 270watt output on the 4 panels. I have these panels 4 feet away from the system outside my garage wall, so heavy wiring isn't so much an issue and is 10g anyway. But I am getting more than 20amp battery currrent even with 3 panel. Its not crappy breakers.

but what I said above

"What I don't understand is what the relationship is between the Battery current and the Solar current. Why in this example is the solar current different than the Battery current?"

Still bothers me. If my Victron is only rated for 20amps do i fry it if battery amps exceed that?
 

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Sundog33 said:
Matt, Forgive me if I'm being rude but I already know the Watts = Volts X Amps because it tells me right on the Panels.
16.77Volts / 6.5Amps /100watts. I don't have to calculate anything or so I thought. Parallel doubles the Amps and Series doubles the Volts.

What I don't understand is what the relationship is between the Battery current and the Solar current. Why in this example is the solar current different than the Battery current?
Click to expand...
I suspect that screen isn't accurate.
 
Sundog33 said:
Matt, Forgive me if I'm being rude but I already know the Watts = Volts X Amps because it tells me right on the Panels.
16.77Volts / 6.5Amps /100watts. I don't have to calculate anything or so I thought. Parallel doubles the Amps and Series doubles the Volts.

What I don't understand is what the relationship is between the Battery current and the Solar current. Why in this example is the solar current different than the Battery current?
Click to expand...
The solar voltage is higher than the battery voltage, so the panels can produce a given amount of power with a lower current.

To get that power into your battery the charge controller takes higher voltage and lower current from the panels and converts it to lower voltage higher current.

You were getting 270w before the breaker popped, if you do the math 270w at battery charge voltage of around 14v is just about 20 amps.

As matt mentioned the charge controller will be maxed out at 20a. You won't damage the controller but it won't make anymore power regardless of how many panels you add.
 
As sunshine_eggo said, those are crappy so called car audio circuit breakers, not likely to have 20A holding current rating.
As you can see, the battery charging current is only around 11A as shown in your picture so that should not have trip the 20A breaker.
The MPPT charger you have is basically a smart buck converter that converts high Voltage low PV panel current to battery charging Voltage and high current.
For example (ignore conversion loss for now), you have 18V at the MPPT PV input and it is solar charge controller is drawing 5A from the panel, the charge controller will buck down the 18V into 13V and able to deliver 6.92A to the battery.
18V x 5A = 90W input power to the solar charge controller, so the battery charging current @13V = 90W/13V = 6.92A

Per your picture:
PV side 28.8V x 5.5A = 158W, battery side 158W/13.5V = 11.73A of battery charging current.
 
Last edited:
Charleswgibbs said:
The solar voltage is higher than the battery voltage, so the panels can produce a given amount of power with a lower current.

To get that power into your battery the charge controller takes higher voltage and lower current from the panels and converts it to lower voltage higher current.

You were getting 270w before the breaker popped, if you do the math 270w at battery charge voltage of around 14v is just about 20 amps.

As matt mentioned the charge controller will be maxed out at 20a. You won't damage the controller but it won't make anymore power regardless of how many panels you add.
Click to expand...
Thanks. Makes sence
 
So if you look at the Victron you have 5.5amps coming for my the panels. When it gets to the BMS its twice that much 11.18amps.
So you propose that at the controller it reverses the power to get me amps going. Which limits me to how many panels I can attach. I can live with that.

I was hoping someone would tell me that the battery breaker had nothing to do with the 100/20 side of the controller and that I could put a 50amp breaker, oh well. panels are cheap these days.

Thanks all
 
You can and should get a higher rated breaker assuming the cable it's on is also equally rated. That will allow your charge controller to put out it's maximum power without tripping the breaker.

But as was said before the max output of the controller is only 20a so if you want to utilize the full 400w of panels, or anymore in the future, you'll need to add an additional charge controller or replace the current one with a higher rated model.

To charge with 400w you'd need roughly 30a of charge current, getting another 20a controller would get you there and allow a bit of expansion
 
Charleswgibbs said:
You can and should get a higher rated breaker assuming the cable it's on is also equally rated. That will allow your charge controller to put out it's maximum power without tripping the breaker.

But as was said before the max output of the controller is only 20a so if you want to utilize the full 400w of panels, or anymore in the future, you'll need to add an additional charge controller or replace the current one with a higher rated model.

To charge with 400w you'd need roughly 30a of charge current, getting another 20a controller would get you there and allow a bit of expansion
Click to expand...
I had thought just go to the next Victron higher. But with the added panels I was also experiencing top out on my battery at 14.3volts and then the Charger would go into float mode and not charge anymore, even tho the battery was only 80% full. My option is upgrading the charger probably wouldn't help unless I upgraded the battery bank too. One of these days I'll pony up for the new EG4 system. When I get my Tesla : )

Thanks
 
Bud Martin said:
As sunshine_eggo said, those are crappy so called car audio circuit breakers, not likely to have 20A holding current rating.
As you can see, the battery charging current is only around 11A as shown in your picture so that should not have trip the 20A breaker.
The MPPT charger you have is basically a smart buck converter that converts high Voltage low PV panel current to battery charging Voltage and high current.
For example (ignore conversion loss for now), you have 18V at the MPPT PV input and it is solar charge controller is drawing 5A from the panel, the charge controller will buck down the 18V into 13V and able to deliver 6.92A to the battery.
18V x 5A = 90W input power to the solar charge controller, so the battery charging current @13V = 90W/13V = 6.92A

Per your picture:
PV side 28.8V x 5.5A = 158W, battery side 158W/13.5V = 11.73A of battery charging current.
Click to expand...
this was not at full power. Obviously I could not take a capture when it was tripped. Again crappy Breakers are not the issue. They are doing their job tripping when sensing 20amps. But thanks
 
Mattb4 said:
Panel voltage and amps going to your SCC is converted to battery voltage and amps based on wattage. Say you have 32v of solar at 12.4a. That is 396 watts into your SCC. Now at your battery 396 watts = battery charge voltage (I am guessing here 14v for 12v battery) X Amps solve = 28.3a Your breaker is overloaded.

No matter how you wire things W=VA
Click to expand...
I see what your saying here. Even with 3 panels at peek could be very close to 20amps. What I wasn’t understanding was the SCC conversion. Thanks
 
Looks like you have got it.

Keeping in mind the conversion to and from differing voltages is also important if you are running a charger from grid. Say you have a 20a 12vDC charger that plugs into a 120vAC outlet. Does it draw 20a at 120v? No it draws 2a. (slightly more due to conversion losses) the wattage is the same however. 120v X 2a =240w just as 12v X 20a = 240w
 
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