Victron Energy: Alternator/Solar Charging - LFP Battery System

[shade]

Question: Should a manual disconnect switch be placed between the panel & solar charge controller, or the charge controller & battery?

I'm thinking it should be between the panel & charge controller, so if the panel is disconnected for servicing, the charge controller isn't getting power pumped into it from the panel.

Victron - Wiring Unlimited has an answer about circuit protection on page 31 that seems applicable:

"Location of the PV array circuit breakers: A fuse needs to be located between a PV array and the solar charger. Please check with the local authorities, regulations per application and country will vary."

 

[SBDuller]

my current set up has a fuse before and after the SC. and the next revised set-up will also. i think it has been said on this forum that neither are necessary...'regulations per app will vary'

 

[shade]

my current set up has a fuse before and after the SC. and the next revised set-up will also. i think it has been said on this forum that neither are necessary...'regulations per app will vary'

What benefit is offered by adding a fuse after the SC?

I figure a switching breaker between the PV panel & SC, and a main fuse at the battery, with a main manual battery disconnect, will be enough protection and flexibility. I'll also have a BatteryProtect module in the circuit to automatically disconnect all charge sources if something goes off. Should I be more concerned about protection between the SC & battery?

 

[luthj]

You must have a fuse or Circuit breaker between the solar controller and the battery. Ideally as close to the battery as reasonable. While the solar charger/controller is a current source, it is limited to whatever the panels can produce, which is 99.9% of the time, less than the limits of the wire.

The battery on the other hand, can produce 1000s of amps of fault current, which can cause fires, arcing, massive damage. It is possible for the wiring, or internal failure of the solar controller to short circuit the battery, causing fire risk. A fuse on the battery side protects against this.

The same goes for the solar panels, they are current limited to Isc. On vehicle mounted single arrays, the worst case fault current is well below the wiring limits, so there is no reason to have a fuse between the panels and the controller.

On larger systems with multiple parallel arrays, or strings, it can be possible for fault current from the other strings to flow through a single string. Depending on panel and wiring sizing this can exceed the limits of the wiring, and create a fire risk. In those situations a fuse for each string is required.

 

[shade]

You must have a fuse or Circuit breaker between the solar controller and the battery. Ideally as close to the battery as reasonable. While the solar charger/controller is a current source, it is limited to whatever the panels can produce, which is 99.9% of the time, less than the limits of the wire.

The battery on the other hand, can produce 1000s of amps of fault current, which can cause fires, arcing, massive damage. It is possible for the wiring, or internal failure of the solar controller to short circuit the battery, causing fire risk. A fuse on the battery side protects against this.

The same goes for the solar panels, they are current limited to Isc. On vehicle mounted single arrays, the worst case fault current is well below the wiring limits, so there is no reason to have a fuse between the panels and the controller.

On larger systems with multiple parallel arrays, or strings, it can be possible for fault current from the other strings to flow through a single string. Depending on panel and wiring sizing this can exceed the limits of the wiring, and create a fire risk. In those situations a fuse for each string is required.

So fusing both sides of the solar controller is a good idea. I'll have a 300A main fuse at the battery as a fail safe for it, but that won't necessarily stop a fault from damaging the solar controller & panel. I may use switching breakers so they can function as disconnects, too. Thanks, guys.

 

[luthj]

Basically, you don't need a fuse on the solar to controller side, at least not for a sub 1kw system on a vehicle (not grid tie etc). A single fuse or breaker on the battery side of the solar controller will provide all the necessary protection, assuming it is properly sized to protect the wiring.

The NEC has some discussion of this for small systems, I can't find the relevant text right now. There simply isn't any reasonable faults that would be protected by a solar fuse for a single string, or small system.

 

[SBDuller]

What benefit is offered by adding a fuse after the SC?

I figure a switching breaker between the PV panel & SC, and a main fuse at the battery, with a main manual battery disconnect, will be enough protection and flexibility. I'll also have a BatteryProtect module in the circuit to automatically disconnect all charge sources if something goes off. Should I be more concerned about protection between the SC & battery?

The basic set-up for mine does not have a main switch/breaker between SC and battery, so the fuse instead. the MPPT manual just said fuse before and after. agree with putting terminal fuse on battery, then main switch

 

[SBDuller]

In following the PKYS blog he uses 300A terminal fuse on the 200Ah battery, and his 2/0 wire has 330 Ampacity. I'm thinking downsize that terminal fuse for 100Ah battery, to 200A or 250A.

 

[luthj]

The max fuse size is always determined by the smallest wire it protects. Going lower is acceptable if desired. Obviously you do not want to exceed about 65-75% of the fuses rating for continuous current. A few minutes at 100% is acceptable for fuses, but generally designing a system with larger wire would be suggested if that is a regular occurrence.

 

[shade]

In following the PKYS blog he uses 300A terminal fuse on the 200Ah battery, and his 2/0 wire has 330 Ampacity. I'm thinking downsize that terminal fuse for 100Ah battery, to 200A or 250A.

I don't think the Ah rating of a battery is as much of a concern as the maximum or recommended allowed discharge current.

I'm looking at the terminal fuse with regard to the my battery's maximum allowed discharge current of 320A. Using a 300A fuse will protect the battery as well as the 2/0 AWG wire leading from it to the main + busbar. All loads will be connected to a Blue Sea SafetyHub 150 fuse box, which will be running off the main busbars. I could downsize that fuse closer to the recommended allowed discharge current of 160A, though. Maybe 200A would be more appropriate.

Except for the Orion DC-DC charger, all of the Victron boxes arrived yesterday. I really need to finish my diagram and order the connecting bits.

 

[Alloy]

I don't think the Ah rating of a battery is as much of a concern as the maximum or recommended allowed discharge current.

I'm looking at the terminal fuse with regard to the my battery's maximum allowed discharge current of 320A. Using a 300A fuse will protect the battery as well as the 2/0 AWG wire leading from it to the main + busbar. All loads will be connected to a Blue Sea SafetyHub 150 fuse box, which will be running off the main busbars. I could downsize that fuse closer to the recommended allowed discharge current of 160A, though. Maybe 200A would be more appropriate.

Except for the Orion DC-DC charger, all of the Victron boxes arrived yesterday. I really need to finish my diagram and order the connecting bits.

I'd fuse at 200A or figure the max loads and wire/fuse 20% above that and buy extras.

 

[dreadlocks]

I have a 200A Blue Sea Terminal Fuse on mine, max loads are much less than that but there is potential for the inverter to drive it that high intermittently for anything that has a heavy startup surge.. if it goes over it, I definitely want it to trip asap as it has no business pulling that much, even for a few seconds so something must have gone terribly wrong.

My wiring to bus bars and distribution systems from battery are good for >400A, so fuse will trip long before any wires get compromised.

 

[shade]

I have time to be nearby during the process, so I decided to do an initial charge of my 160Ah LFP battery. I have full manual control of voltage and amperage up to 30V / 20A. I'm in no hurry to take the battery to 100% SOC.

How do these charge parameters look?

70° F: Battery temperature
13.470V / 10A: Initial charge voltage/amperage
3.30V: Initial charge voltage per cell

10A: Amperage limit
13.8V: Voltage limit

 

[luthj]

Seems reasonable to me. For the final top balance, 3.6Vpc is a commonly accepted figure. Some internal balance setups don't start shunting current around until the 3.5VpC level, but it varies a lot between brands.

 

[shade]

Seems reasonable to me. For the final top balance, 3.6Vpc is a commonly accepted figure.

Thanks.

I figure I'll let this cycle run for however long it takes (I started a stopwatch out of curiosity), let the battery rest overnight, and do a final top balance cycle tomorrow. The cells are reporting balanced now, so top balancing may not take long. Keeping an eye on things with the VictronConnect app is slick.

I really like this power supply. With coarse & fine adjustment by knob, it's simple to set up the charging routine to exactly what I want to the thousandths. I'll get my AGM start battery to 100% once I'm done with the house battery.