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Draft solar set up, please have a look

totalconfusion

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Dec 24, 2020
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Howdy partners,

I'm drafting up a system and wanted to run it past some some of your wise minds.
I've attached what could be charitably called a wiring diagram.


1. If you could point out any issues with wrong connections and/or bad wire sizing

2. Does the MPPT Battery negative connection go to the negative load side of the shunt OR strait to battery negative?

3. Given the panel specs in the top left of the diagram, with a 2S2P set up. Will the MPPT handle it? I calculated I could run up to 2S3P

3. Help me insert the battery protect in to the system

4. Is there any decent software for making wiring diagrams?

5. The Battery Protect will be a Victron Smart BatteryProtect 100A
(https://www.victronenergy.com/uploa...art-Battery-Protect-65-A--100-A--220-A-EN.pdf)


Thanks heroes!
 

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1. If you could point out any issues with wrong connections and/or bad wire sizing.
2AWG should be used for the 100A connections between the battery and the Distribution Fuse Block. 12AWG wire should be used for the 15A connection between the charge controller and the battery
2. Does the MPPT Battery negative connection go to the negative load side of the shunt OR strait to battery negative?
The shunt can only measure current that passes through it. Typically the charge controller is connected to the load side of the shunt. In this configuration the shunt can measure both charge and discharge current in and out of the battery thus keeping an accurate SoC. However, when the solar panels are producing, any current that goes directly to the loads will not be measured by the shunt.
3. Given the panel specs in the top left of the diagram, with a 2S2P set up. Will the MPPT handle it? I calculated I could run up to 2S3P
Couple of issues: The charge controller is rated for 100V maximum and the panels have a Voc of 45.4V x 2 = 90.8V. Datasheet Voc values are measured at STC which is 25 deg. C. At 0 deg. C the Voc will increase by about 7 volts. What is the coldest outdoor temps you expect.

The charge controller is rated at 220W max for a 12V system, any extra power will be wasted. You really only need 2 panels connected in parallel to the charge controller. To fully utilize all 4 panels you need 2 charge controllers which will provide up to 30A of charging. As long as the battery is at least 100Ah then your charge rate will be acceptable at 0.3C.
3. Help me insert the battery protect in to the system.
I believe the battery protect will monitor both amperage and voltage and will disconnect either on high current or low voltage (which roughly correlates to SoC) so the battery doesn't get too low. Do you really need this functionality if the shunt is monitoring SoC? If not then a fuse would be a much easier solution as you noted on the drawing.
As to your question specifically: The Batt Protect device is uni-directional and would be inserted into the Positive cable shown on your diagram connecting Battery Pos+ to the M5 ring terminal on the Distribution Fuse Block. Follow the Victorn wiring diagram as current will only flow one direction when the device is in the ON state.
4. Is there any decent software for making wiring diagrams?
That is an excellent question, wish I had an answer. Haven't searched for suitable software lately but is on my to do list.
 
Thanks for your response mate!

1. 2AWG should be used for the 100A connections between the battery and the Distribution Fuse Block. 12AWG wire should be used for the 15A connection between the charge controller and the battery
I've looked at a bunch of different DC Max Amperage charts that range from 4AWG to 1AWG - I'll err on the side of caution and use 2AWG as you suggest. What resources do you refer to when calculating these things? I was surprised to see such variety in the charts I was looking at.

2. The shunt can only measure current that passes through it. Typically the charge controller is connected to the load side of the shunt. In this configuration the shunt can measure both charge and discharge current in and out of the battery thus keeping an accurate SoC. However, when the solar panels are producing, any current that goes directly to the loads will not be measured by the shunt.
In the attached diagram the MPPT negative battery connection is attached to the load side of the shunt. I'll keep it this way. Are you suggesting I would need multiple shunts in order to accurately measure both discharge and PV charge? I would get the most utility out of measuring discharge, but if I want to see the PV charge I guess I can turn off all the loads during the day and have a look, then switch them back on. Have I got this right? Sorry I'm a little confused.

3. Couple of issues: The charge controller is rated for 100V maximum and the panels have a Voc of 45.4V x 2 = 90.8V. Datasheet Voc values are measured at STC which is 25 deg. C. At 0 deg. C the Voc will increase by about 7 volts. What is the coldest outdoor temps you expect.

The charge controller is rated at 220W max for a 12V system, any extra power will be wasted. You really only need 2 panels connected in parallel to the charge controller. To fully utilize all 4 panels you need 2 charge controllers which will provide up to 30A of charging. As long as the battery is at least 100Ah then your charge rate will be acceptable at 0.3C.
I agree 90.8V is quite close for my liking. The location is outback Australia. The coldest outdoor temperature on record is -0.3° but it never really gets that low during the day. The panels are second hand, would that mean the output will probably be lower than new? I understand the way forward right now you're suggesting is just to use two panels in parallel, but I will be using more of the same panels in series in the future so would like to know if I can get away with 90.8V on a 100V MPPT

Where do you get the MPPT 220W max from? Is this the "Nominal PV power, 12V 1a,b)" in the manual? Do you know how this is calculated?

The batteries are 100AH and will charge at up to 0.5C comfortably. Although I understand the 100/15 MPPT I'm using right now will only put out 15A not 50A

I have 8 of these panels total so my guess is in the future I'll be running a Victron 100/30 or 100/50 MPPT and using all 8 panels with a 2S4P set up and running a 24V or 48V system.

3. I believe the battery protect will monitor both amperage and voltage and will disconnect either on high current or low voltage (which roughly correlates to SoC) so the battery doesn't get too low. Do you really need this functionality if the shunt is monitoring SoC? If not then a fuse would be a much easier solution as you noted on the drawing.
As to your question specifically: The Batt Protect device is uni-directional and would be inserted into the Positive cable shown on your diagram connecting Battery Pos+ to the M5 ring terminal on the Distribution Fuse Block. Follow the Victorn wiring diagram as current will only flow one direction when the device is in the ON state.
My impression of the Victron Smart BatteryProtect 100A is that it shuts off any loads from the battery to protect the battery from damage occurring due to discharging the battery too much. I was only aware of it sensing voltage which as you say, is a rough corollary for SoC.

The shunt is monitoring and pushing to a gauge. The need for a BatteryProtect would be realised if somebody left the lights on and forgot about it, thus discharging the battery. I don't see how a fuse could provide the same functionality?

The 100A fuse I thought about putting between the + battery and positive ring terminal on the distribution board was only the prevent the cumulative fused loads of 30A getting any higher than 100A. The board has about 12 outputs each rated up to 30A but the whole unit can't go over 100A.



Thanks so much, I really appreciate all your help

How's the weather in California?
 
I've looked at a bunch of different DC Max Amperage charts that range from 4AWG to 1AWG - I'll err on the side of caution and use 2AWG as you suggest. What resources do you refer to when calculating these things? I was surprised to see such variety in the charts I was looking at.
Ampacity charts vary somewhat due to 2 factors. Max voltage drop value used in preparing the chart, usually 2 to 3%, and temp rating of the insulation. I prefer to calculate voltage drop directly and keep it below 2%. I generally verify by taking a quick cross reference look at an ampacity chart on the most conservative 60 deg C column. Here is a voltage drop calculator. https://www.southwire.com/calculator-vdrop
In the attached diagram the MPPT negative battery connection is attached to the load side of the shunt. I'll keep it this way. Are you suggesting I would need multiple shunts in order to accurately measure both discharge and PV charge? I would get the most utility out of measuring discharge, but if I want to see the PV charge I guess I can turn off all the loads during the day and have a look, then switch them back on. Have I got this right? Sorry I'm a little confused.
Yes, but the Victron charge controller has a communication port so if you know the total output of the charge controller AND the shunt is measuring how many watts are charging the battery the difference is what is going to the loads directly and bypassing the shunt. You really don't need a second shunt.
I agree 90.8V is quite close for my liking. The location is outback Australia. The coldest outdoor temperature on record is -0.3° but it never really gets that low during the day. The panels are second hand, would that mean the output will probably be lower than new? I understand the way forward right now you're suggesting is just to use two panels in parallel, but I will be using more of the same panels in series in the future so would like to know if I can get away with 90.8V on a 100V MPPT.
90.8V is below the max so is perfectly fine BUT at 0 deg. C the voltage would be approx. 97 to 98V. This is dangerously close to the limit. Its your equipment, you have to choose how to use it. Since the charge controller only needs PV at +5V above battery voltage to work, I would put the 2 panels in parallel.
Where do you get the MPPT 220W max from? Is this the "Nominal PV power, 12V 1a,b)" in the manual? Do you know how this is calculated?
Watts = Amps x Volts. When charging a 12V battery at 14.7V and 15A translates to 220W. I would suggest charging the battery at no more than 14V so realistically the functional max output of the SCC is 14V x 15A = 210W.
The batteries are 100AH and will charge at up to 0.5C comfortably. Although I understand the 100/15 MPPT I'm using right now will only put out 15A not 50A
OK
I have 8 of these panels total so my guess is in the future I'll be running a Victron 100/30 or 100/50 MPPT and using all 8 panels with a 2S4P set up and running a 24V or 48V system.
Higher voltage is generally better as it reduces amperage which allows one to use smaller, less expensive and easier to work with wire and cable.
The shunt is monitoring and pushing to a gauge. The need for a BatteryProtect would be realised if somebody left the lights on and forgot about it, thus discharging the battery. I don't see how a fuse could provide the same functionality?
Correct the fuse does not provide the same functionality so the Batt Protect is a good option to prevent unwanted battery discharge to low SoC.
The 100A fuse I thought about putting between the + battery and positive ring terminal on the distribution board was only the prevent the cumulative fused loads of 30A getting any higher than 100A. The board has about 12 outputs each rated up to 30A but the whole unit can't go over 100A.
The fuse is good idea as it will provide fast action in case of an accidental dead short.
How's the weather in California?
Typical "June Gloom" as we call it. Actually starts in May with foggy, overcast mornings and afternoon Sun. It a weird time of year where in the car you would use the heater in the morning and AC in the afternoon. Temps range from 55 F to 80F so there isn't much heating or cooling demand for a well insulated house. Most of the solar production goes out to the utility as NET metering credits until later in the summer when AC is needed.
 
To confirm, Victron Battery Protect is a fet switch programmed to open if the voltage falls below the programmed voltage . It's a 'one way ' device connected between power source and load, cannot be used to power inverters or similar with high surge currents.
In no way does it control current.
Assuming the DC loads needing protection are fed from the blade fuse box connect the Battery Protect between the shunt load output and the fuse box.
Mike
 
Yes, its a one way device so polarity matters, it gets confusing. The Victron wiring diagrams shows the Batt Protect inserted on the Pos wire (high side), in front of the load. If it is placed between the shunt and load per totalconfusion's wiring diagram then the Batt Protect is on the Neg wire (low side) behind the load. In this configuration current flowing out of the load goes to the Batt protect IN and Batt Protect OUT goes to the shunt.
 
Any suggestions for the type of fuse the 100A should be? Something like this? Amazon

So I'm still not 100% how to hook up the BatteryProtect. Should it be between the 100A fuse and the battery positive? BatteryProtect Datasheet

I also think I should be putting in a circuit breaker rated for high DC voltage between the branch connectors and MPPT. Would this be good practice? Any suggestions or links to an adequate breaker and housing?

Glad to hear you're saving on the electricity bills over there :) Well insulated houses in Australia are virtually non-existent.
 
Any suggestions for the type of fuse the 100A should be? Something like this? Amazon
I prefer breakers vs. fuses and the product on Amazon has good reviews so should be a good choice.
So I'm still not 100% how to hook up the BatteryProtect. Should it be between the 100A fuse and the battery positive? BatteryProtect Datasheet
Yes, that is where I would put it per the datasheet. It would still work if installed on the Neg cable if polarity is observed properly.
I also think I should be putting in a circuit breaker rated for high DC voltage between the branch connectors and MPPT. Would this be good practice? Any suggestions or links to an adequate breaker and housing?
Its nice to have a means of disconnect on anything above 50V DC. A switch would be fine if you want that convenience, I don't think a breaker or fuse is necessary in your simple set up. If the system is expanded and there are more than 2 parallel PV arrays, a combiner box with breakers would be recommended in that case.
 
I don't think I understand the distinction between a circuit breaker and a switch. Do circuit breakers necessarily have a set current at which they will pop where as a switch is purely manual in function? When would a PV array experience an over current condition? Short circuit or lightning strike?

I'm looking at combiner boxes and they seem to include:
surge protection (SPD)
A bunch of circuit breakers (effectively fuses)
and a DC switch

Could I just get a say 15amp DC circuit breaker and put it between the branch connectors and the MPPT, effectively giving me over current protection AND the ability to use it like a switch? Seems like the cheap option that gives me the most. Only thing it would lack is the SPD, how necessary is it?

Am I right in thinking of a circuit breaker as a fancy switch? Is 15A a good value? Are there any particular types of circuit breaker I should be looking for or just make sure it's for DC?

If I can go with the circuit breaker idea I assume I'd need a 2Pole breaker and run the positive and negative on the respective sides of the unit.

I can't thank you enough, I had about a million questions at the start of this and now I'm really confident going forward.
 
I don't think I understand the distinction between a circuit breaker and a switch. Do circuit breakers necessarily have a set current at which they will pop where as a switch is purely manual in function? When would a PV array experience an over current condition? Short circuit or lightning strike?
Yes, a Switch just has an On-Off function, a circuit breaker is also called an Over Current Protection Device.
A PV array generally has 2 electrical components to consider.
1) Cells that produce electricity and are sandwiched between a backer board of some type and a protective, transparent top layer like glass that lets the light through. PV cells have relatively high internal resistance so their short circuit current is not significantly higher than their maximum operating current. Thus its virtually impossible for a PV panel in normal operation, to produce a large current spike. In larger arrays where there are multiple sets of panels and a bundle of wire that could short out, its recommended, even required, to use a combiner box with breakers.
2) Most PV panels have an aluminum frame which is insulated from the PV output but is grounded due to potentially receiving lightening strikes.

Its worth mentioning that in most cases the inverter instructions stipulate that neither the Pos+ or Neg- wire from the PV should be grounded. However, the aluminum PV frame and any metalic conduit must be grounded. In electrical speak there is a "system" ground and an "equipment" ground. They are not the same thing.
I'm looking at combiner boxes and they seem to include:
surge protection (SPD)
Sometimes called a Transient Voltage Surge Suppressor (TVSS) Its a good safety device to have if your area experiences frequent lighting storms.
Could I just get a say 15amp DC circuit breaker and put it between the branch connectors and the MPPT, effectively giving me over current protection AND the ability to use it like a switch? Seems like the cheap option that gives me the most.
2 pole breakers are customarily used for PV because as stated above, neither "system" wire is grounded so could have potential compared to ground thus a 2 pole breaker opens the connection on both conductors. If you do the 2S configuration a 10A breaker is more appropriate vs. 2P then 15A. This is based on the PV specs in the OP.
Am I right in thinking of a circuit breaker as a fancy switch? Is 15A a good value? Are there any particular types of circuit breaker I should be looking for or just make sure it's for DC?
The breaker has to be rated for the voltage ts being used at and some brands of breakers are polarized, the direction of current flow matters with regard to the ability to extinguish a DC arc. Follow the instructions.
 
Yes, a Switch just has an On-Off function, a circuit breaker is also called an Over Current Protection Device.
A PV array generally has 2 electrical components to consider.
1) Cells that produce electricity and are sandwiched between a backer board of some type and a protective, transparent top layer like glass that lets the light through. PV cells have relatively high internal resistance so their short circuit current is not significantly higher than their maximum operating current. Thus its virtually impossible for a PV panel in normal operation, to produce a large current spike. In larger arrays where there are multiple sets of panels and a bundle of wire that could short out, its recommended, even required, to use a combiner box with breakers.
2) Most PV panels have an aluminum frame which is insulated from the PV output but is grounded due to potentially receiving lightening strikes.
Thank you, I will have to consider grounding the PV framing.

2 pole breakers are customarily used for PV because as stated above, neither "system" wire is grounded so could have potential compared to ground thus a 2 pole breaker opens the connection on both conductors. If you do the 2S configuration a 10A breaker is more appropriate vs. 2P then 15A. This is based on the PV specs in the OP.
The breaker should be the same as the MPPT "Max. PV short circuit current" right?

Legend, thanks a bunch!
 
General rule, Breakers are sized at 125% of the maximum continuous current. Of course breakers are sized in 5 or 10Amp increments. For your application a breaker rated approx the same as the short circuit current of the panels would be appropriate.
 
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