I’ve designed the system as shown in the attached diagram, using components I already have, and would like to protect the whole setup by adding a BatteryProtect.
The battery is charged via the SmartSolar MPPT, which is in turn powered by a charger with a 48 V output, connected to the alternator.
When the engine is off, the SmartSolar isn’t powered; when the engine is running, it’s supplied with 48 V.
Now, what happens to the solar MPPT if the lithium battery’s MPPT switches off because the battery is fully charged?
Does the SmartSolar MPPT switch off too, or does it keep supplying power?
Will the BatteryProtect protect me in the event of a failure of the solar MPPT?
A Battery Protect protects a battery from being completely discharged, but not from overcharging. It was developed for lead-acid batteries and is generally unnecessary with LiFePO4 batteries that have a BMS. The BMS disconnects the battery when it is empty (undervoltage) as well as when it is full (overvoltage).
Hi Karl, I read in the Battery Protect specifications that it can also disconnect the connection when it detects a voltage above 16V.
So, if the BSM in the Smart Solar were to fail and, for example, 48V were to reach the battery-side output, the Battery Protect would immediately disconnect the connection, protecting everything downstream.
I’ve also read about cases where a failure of the Smart Solar’s BSM caused quite a disaster downstream, even resulting in fires starting.
I look forward to hearing any further feedback and opinions.
The crowbar circuit will be difficult to size. The diode must be rated for a continuous current of 20 A and cooled accordingly; pay attention to a low voltage drop at 20 A. The thyristor should be generously rated and have as high a dI/dt rating as possible, because a larger capacitor at the SmartSolar output needs to be discharged. The fuse will not trip, because the currents are limited to a maximum of 15 A from the DC-DC converter and 20 A from the SmartSolar. The thyristor will therefore have to carry the current continuously (cooling required) until someone switches it off manually or the DC-DC converter stops supplying current. It is questionable whether a continuous short circuit is safe for the components upstream. The Zener diode only needs to be rated for the thyristor’s trigger current, which is typically less than 50 mA.
That Z1 is overkill for the trigger current of the SCR. The SCR is undersized at 25A it will probably blow before the fuse does. So you’ll want to change that.
Don’t use a SmartSolar MPPT as a DC-DC charger; that’s not what it’s for and multiple degrees of system damage could be caused by improper use of the component.
Please just get a 48/12 DC-DC charger instead; they’re readily available from multiple manufacturers including Victron themselves, specifically the ORI481224120
That’s right, Justin. I don’t use the MPPT as a DC-DC; the 48V are supplied by the Aferiy DC-DC charger connected to the camper’s alternator, as described in one of my earlier posts.
The MPPT receives 48 volts as if it were connected to a 48V 450W solar panel, so around 10A.
That’s what I mean, you are using it as a DC-DC charger, using the 48v output from the Aferiy power station battery as PV input to the solar controller, using the solar controller to step down and charge the 12v battery. The problem is that the Aferiy power station battery is not a solar panel and will not react like a solar panel when the MPPT shorts the PV input together. Please use a correct 48-to-12 DC-DC charger for this purpose instead, as that will not short the input together and will not cause potentially multiple cascading and dangerous failures within your system.
The Aferiy DC060 isn’t a power station; it’s a DC-DC converter that draws power from the alternator at around 14 V and converts it to a stable 48 V output, with a maximum power of 450 W.
So if I connect the 48 V output of the DC060 to the PV input of the SmartSolar MPPT, isn’t that the same as having a 48 V solar panel?
There won’t be any voltage fluctuations, since the DC060 provides a stable 48 V, as if the PV panel were illuminated by a fixed light source shining directly onto it.
Ah, I see… I thought that was one of the Aferiy power stations. Hmmm, well… still not a supported or proper usage of an MPPT, and could still potentially cause damage to components since, again, a solar controller can and should, in various situations, short its PV input together; solar panels are fine with that, anything at all other than a solar panel will, in general, respond poorly.
I would still advise just getting the proper component instead, which would be a 48 to 12 DC-DC charger like ORI481224120, to ensure that your system is designed with components being used for their intended purposes, thus preserving warranty coverage as well as overall system behavior.
Why not simply use an “Orion-Tr Smart 12/12-18A (220W) Isolated DC-DC charger”? That way, there’s no excessively high voltage in the system that you need to protect against. It also manages shutdown when the alternator is off.
