MajicDiver
Solar Enthusiast
Would someone be willing to explain why you can’t put 2 EG4 48VDC batteries in series and what would/might happen if you did?
EG4-48VDC in Series
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Jim Burrow
Solar Enthusiast
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If you put batteries of any type in series, the voltage is additive. If your controller is designed for 48v DC and you put 98 vdc to the controller battery dc input, you could damage it or blow a dc fuse or just burn it ups with a nice explosion. However, I have never done this as I'm not a rich person, so what I just mentioned is just theory on my part.
timselectric
If I can do it, you can do it.
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Best case scenario is that a fuse would blow.
Otherwise, it's time for a new inverter.
Otherwise, it's time for a new inverter.
MajicDiver
Solar Enthusiast
What I am considering is connecting them to the PV input of an inverter with a turn on voltage of 50VDC and rated to 600VDC. Looking for a way to use low voltage battery on an inverter that only has high voltage battery input, to reduce costs- HV batteries are expensive
Lt.Dan
Solar Wizard
I dont understand what that would achieve? The PV inputs are just that, an input. How would you charge this 100v battery?
Ampster
Renewable Energy Hobbyist
I thought fuses were over current devices? I guess that is why you described it as “best case“? LOL
MajicDiver
Solar Enthusiast
A separate AC charger, charge manually during daytime then cut it into the inverter with a breaker when desired.
timselectric
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Correct
timselectric
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It would depend on what the voltage rating was for the BMS of the EG4 batteries. Doubtful that they could handle it.
You could build your own high voltage battery. With a high voltage BMS.
No has brought up (edit: @timselectric just beat me to it) that you can't put LiFePO₄ batteries in series unless its BMS supports being put in series. Many can't. Putting two 48V batteries in series is of course 96V. If the BMS in each battery isn't designed to support that voltage you will either cause the BMS to shutdown or worse, to fry itself.
Jim Burrow
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With respect to MajicDiver comment, I'm wondering what would happen. Example take a 39vdc (2ft by 4ft) solar panel and short circuit the leads and you get a ISC of 9 amps. (at least on my panels). So, in theory only 9 amps is available at the PV input terminals.
Now take any battery, 6v, 12v, 24v, 48v, any size, and short their terminals. you will get a massive surge of current and a spark you can't believe. So, then in theory, if you connect any of these batteries to the pv terminal of your controller, I would think that you would destroy the inverter. Again this is just in theory on my part as I have never tried it and can't afford to buy a new controller/inverter.
But then on the other hand, when you connect your solar panel to the input of your controller, only the current that would flow is dependent on the load the controller is controlling regardless of how much current is available from the panels.
So maybe, MajicDiver comment isn't so bad after all.
Now take any battery, 6v, 12v, 24v, 48v, any size, and short their terminals. you will get a massive surge of current and a spark you can't believe. So, then in theory, if you connect any of these batteries to the pv terminal of your controller, I would think that you would destroy the inverter. Again this is just in theory on my part as I have never tried it and can't afford to buy a new controller/inverter.
But then on the other hand, when you connect your solar panel to the input of your controller, only the current that would flow is dependent on the load the controller is controlling regardless of how much current is available from the panels.
So maybe, MajicDiver comment isn't so bad after all.
MajicDiver
Solar Enthusiast
I’m just trying to see if there is a issue that prevents doing it. To address max short circuit current rating of inverter input use a breaker that trips before that current level between the battery and inverter PV input.
The BMS may not be able to shut off or interrupt current flow if series string voltage exceeds maximum MOSFET switch voltage of BMS. If BMS uses 100V rated MOSFETs then with 3 of 48V batteries in series they will enter avalanche mode and continue passing current even if BMS tries to shut them off. Then you end up without short circuit, under voltage and over voltage protection. Also if the battery or BMS data connection is negative terminal bonded to the metal case then you end up with a short circuit if you mount 2 rack batteries together or if you daisy chain the data lines. Don't do it unless the battery is designed to be connected in series.
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Yes, you are the professional one to reply the questions. Also have the 48V100AH battery in series type, but not this kind of structure.
MajicDiver
Solar Enthusiast
Thanks, and the EG4 manuals clearly indicate you can only series the smaller voltage models up to 48 vdc and not the 48 volt model. Does anyone know of a brand that can go to 72 or perhaps 96 volts?
MajicDiver
Solar Enthusiast
That’s what I might end up doing- but I am a mechanic by nature not an electrician and would prefer to achieve it with “off the shelf” components as opposed to actually building a complete battery.
timselectric
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Good luck
I don't think that there's an off the shelf option available. At least not that I am aware of.
In somewhat similar vein, what would it take to connect an ElectricVehicle (EV) pack, ~360-400vdc, to the PV-INPUT of a hybrid inverter ? say a 5000-w mpp5648gk, which has 500vdc PV input ? for sure a DC circuit breaker. A simple 10A DC breaker would protect overdrawing the EV pack to 4000-w or so. Am wondering if some kind of current limiting is needed. Thanks
Why you need the high voltage system? The high voltage battery must match with high voltage inverter, you can check the Sofar, Growatt, Luxpower and some other inverter brand which have the small power but high voltage version for home energy storage system. At this situation, the battery pack also should be high voltage system, there isn't the BMS supplier willing to provide this to the individul clients.
So DIY is not the solution to decrease the cost.
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