JBD/Overkill based system

[Aphers]

So I've been seriously considering either Electrodacus or Overkill/JBD for my BMS. This is for the domestic electrics on a liveaboard sailing boat.
I came very close to choosing Electrodacus, but it looks like a JBD-based system is going to come in much cheaper, and probably be simpler.

Looking for any advice and feedback on the following basic system design:
- 2x 320w 32v PV in to 40A Epever MPPT
- 2x 100w 12v PV in to Victron 75/15 Smart MPPT
- both MPPTs charging a 4s 280Ah LFP battery, via JBD BMS
- all loads going via the BMS, except the inverter which has a remote switch function and will be driven using SSR from the BMS.
- Aili Battery Monitor for at-a-glance SOC information

The inverter will have its own LVD set pretty high. All the other loads on the system are small- lights, fridge, laptop charger etc.
I know the two sets of panels/MPPTs seem a bit strange. There's a reason for that. The smaller 12v system is going to do two jobs. When the boat is not moving, it will give extra power to the domestic LFP system. When we are underway, it will be switched over to power the lead-acid system which is connected to the engine and the navigation systems. I'm choosing the Victron MPPT here to make the reconfiguration easier- I don't want to mess it up when I change charging profiles.

I do also have a 60A B2B charger. I actually don't know how this will be used. I might need to rely on engine charging more than I hope, in which case the B2B will be used to send power from the SLAs to the LFP system. Or I might find that I have excess power in the LFP and send it the other way. Or I might not need it at all!


My biggest query about the JBD/Overkill is how it handles charging sources. I think the 120A version can take 60A charging current. That is adequate for my 40+15 MPPTs, but only just. Is it risky to run that close to capacity? Second question, when the BMS decides to shut off charging, this can damage the MPPTs, but how big is this risk? I have seen so many conflicting opinions on this point, and so many ways of avoiding it, all of which seem to have their own disadvantages. Genuinely not sure how much to worry about this. The Epever MPPT is only about 10% of the whole system cost, but obviously I don't want to build in a weakness.

 

[John Frum]

Can any/all of the charge sources use remote switching?
I am working on a setup now with 2x 20 bms.
1 for charge and the other for discharge.
Neither in the high current path.

 

[HRTKD]

My biggest query about the JBD/Overkill is how it handles charging sources. I think the 120A version can take 60A charging current. That is adequate for my 40+15 MPPTs, but only just. Is it risky to run that close to capacity? Second question, when the BMS decides to shut off charging, this can damage the MPPTs, but how big is this risk? I have seen so many conflicting opinions on this point, and so many ways of avoiding it, all of which seem to have their own disadvantages. Genuinely not sure how much to worry about this. The Epever MPPT is only about 10% of the whole system cost, but obviously I don't want to build in a weakness.

The Overkill Solar BMS (essentially the JBD, with some connection tweaks, better customer service and a real manual) the charge/discharge is 120 amp continuous. There have been tests to show this works, sometimes well above the rating. Would I run my BMS at the rated amps continuously? No, but it's good to know it can handle it for a while if I need it.

When my BMS turns off the charge, the discharge is still available, so no hard will come to the MPPT.

 

[Aphers]

The Overkill Solar BMS (essentially the JBD, with some connection tweaks, better customer service and a real manual) the charge/discharge is 120 amp continuous. There have been tests to show this works, sometimes well above the rating. Would I run my BMS at the rated amps continuously? No, but it's good to know it can handle it for a while if I need it.

When my BMS turns off the charge, the discharge is still available, so no hard will come to the MPPT.

Thanks. So is the MPPT only at risk when using a common port BMS?

 

[HRTKD]

Thanks. So is the MPPT only at risk when using a common port BMS?

I believe the Overkill Solar BMS is considered a common port BMS. It's just "better". If you want to know more about common/separate port, take a look at this thread:

BMS common port vs seperate port

Can someone explain the difference? When would you want one or the other? Benefits?

diysolarforum.com

 

[Aphers]

Thanks, I think I just about have my head around common vs separate, the JBD seems to be somewhere in the middle.
I'm happy with a fairly high level of manual intervention being required, e.g. reset after a disconnect, so I think the JBD will suit me OK.
Just want to make sure I don't a) run out of charging current capacity, and b) fry my MPPT.

 

[HRTKD]

Thanks, I think I just about have my head around common vs separate, the JBD seems to be somewhere in the middle.
I'm happy with a fairly high level of manual intervention being required, e.g. reset after a disconnect, so I think the JBD will suit me OK.
Just want to make sure I don't a) run out of charging current capacity, and b) fry my MPPT.

The whole cutting off the battery power will fry the MPPT appears to be overblown. Will Prowse has a thread around here where he posted that he couldn't kill any of the many MPPT devices he has by cutting off the battery power. I still do a staged manual shutdown for mine, just in case. Kill power from the PV, then power from the Battery.

 

[Aphers]

The whole cutting off the battery power will fry the MPPT appears to be overblown. Will Prowse has a thread around here where he posted that he couldn't kill any of the many MPPT devices he has by cutting off the battery power. I still do a staged manual shutdown for mine, just in case. Kill power from the PV, then power from the Battery.

Thanks. When you look at my whole system design inc cells, panels, inverter, BMS, batt monitor, and MPPT, the main MPPT is about 10% of the total. It would not be the end of the world if I ever had to buy a replacement, it would just be inconvenient and not something I would want to have to do often if it's easily avoidable.

 

[HRTKD]

Reasonable caution is always reasonable. Sometimes best practices become outdated. There are stories out there of fried solar charge controllers, so I'll continue to follow the best practice of shutting off the PV first.

 

[Aphers]

Update:
I've now got my cells and have top balanced them.
My JBD seems to work, I was using it for the bulk charging.
My solar panel plans have changed a little, as I was offered a deal that I couldn't turn down.

The thing I'm struggling with now is how I can use my JBD so tell an inverter to turn off. The inverter I'm looking at is from Epever and supports remote switching. If I'm understanding correctly, the JBD doesn't actually support external relays, but I can still make this work, just the BMS will no longer have SOC information for the power going to the inverter. That sucks, but is presumably solvable by using a battery monitor?

I'd be very grateful for any advice on this.

 

[williamsk913]

Update:
I've now got my cells and have top balanced them.
My JBD seems to work, I was using it for the bulk charging.
My solar panel plans have changed a little, as I was offered a deal that I couldn't turn down.

The thing I'm struggling with now is how I can use my JBD so tell an inverter to turn off. The inverter I'm looking at is from Epever and supports remote switching. If I'm understanding correctly, the JBD doesn't actually support external relays, but I can still make this work, just the BMS will no longer have SOC information for the power going to the inverter. That sucks, but is presumably solvable by using a battery monitor?

I'd be very grateful for any advice on this.

Look at a large relay as an option. Still need a $40 battery monitor, but if it lost power from BMS it would close circuit. Some inverters have an on off switch that can also be controlled by a relay, but not all remote switches can be used this way.

 

[Aphers]

Look at a large relay as an option. Still need a $40 battery monitor, but if it lost power from BMS it would close circuit. Some inverters have an on off switch that can also be controlled by a relay, but not all remote switches can be used this way.

The inverter I'm considering doesn't have a remote panel, it has a port for an actual remote switch. It also has a rocker switch on the unit itself, so I think I should be OK using a small SSR rather than needing a larger relay carrying the current.