diy solar

diy solar

DC to DC boost converter Question

Shinebox

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Feb 10, 2021
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I'm interested in utilizing the SMA Sunny Boy Storage inverter for a battery bank. I understand that for example the LG Resu HV battery is actually a 48v bank with a DC-DC boost converter that is outputting 400v. I'm assuming that this converter is a bidirectional converter, which would then allow for charging of the batteries. The only one I have been able to find is THIS one. At about $4000 per 2Kw, that's a very expensive proposition. I rather like the idea of building a 48v pack and then boosting the voltage, as it seems inherently safer to deal with, but perhaps the only option for DIY is to actually build a HV pack and then use Batrium, REC, Emus or some other BMS capable of dealing with higher voltage. I haven't been able to find any examples of people using this inverter with anything other than a commercially available battery pack.. perhaps someone knows of such an integration.
 
Please pardon my possible ignorance, but I'm trying to wrap my head around this statement:

"...idea of building a 48v pack and then boosting the voltage, as it seems inherently safer to deal with"...
 
Safer in that the pack itself is not actually high voltage… ie the converter can be disconnected if need be, and setting up the pack with all of the leads for the bms etc would be a little less ass puckering. Also, as for the BMS it would be easier overall to implement too.
 
Safer in that the pack itself is not actually high voltage… ie the converter can be disconnected if need be, and setting up the pack with all of the leads for the bms etc would be a little less ass puckering. Also, as for the BMS it would be easier overall to implement too.

How much loss is in the conversion? It also would be certain that it add more complexity to the overall system, to consider ongoing maintenance down the line. In my personal opinion, sometimes just because some 'can' be done, doesn't always mean it's a good idea to do. I prefer simplicity wherever possible. Is there a specific goal you're trying to accomplish by having this topology, or are there simpler or more traditional topologies that will meet all your design needs without the extra complexity?
 
I only considered this when, as I mentioned in the original post, I heard they this solution is actually being used by LG and possibly others. As for complexity, again building an HV pack may actually be more complex as far as setting up the BMS for all of the cells (100s+ depending on whatever voltage is chosen). There is also the matter of CANbus communication with the Sunny Boy storage, and getting that to work for HV. At any rate, I can always go with a Sunny Island/ Sunny boy setup and do what I want. Just curious to see if anyone has worked with the Sunny Boy storage and integrated it with a diy pack. Please chime in if you have had suck experience.
 
I don't specifically know much about these (other than what I've read from specs docs and whatnot).

I think Hedges is one guy here who knows quite a bit about the Sunny Island / Sunny Boy inverter setups... You could try IM'ing him if he doesn't respond to this thread soon...

I did once look into the idea of a Sunny Island inverter, since it may've had the possibility of interfacing with the battery voltage on my Prius. I had been thinking of building a battery bank based on the higher voltage the Sunny Island supported, and being able to parallel it to my Prius if I wanted, so I could also add more batteries to my car (to make it more like a plug-in hybrid with longer range on electric) and have the option to charge the home bank off the car, or charge the car off the home bank if desired, but eventually I decided I have bigger fish to fry on another off-grid project, that working on a plugin hybrid conversion is not feasible for me to focus on for now, so I never took the research any further for the time being.
 
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For Sunny Boy Storage, my first thought was a 128s (more or less) battery with LiFePO4 cells. REC BMS can be assembled in building blocks that large and larger. I don't know for sure that REC's BMS is also compatible with Sunny Boy Storage, could be a different protocol.

Data sheet says, "Max. short-circuit current per input 40 A". Compare THAT to 20kA at 400V from a lithium battery! At least a really good fast fuse required. Could maybe filter with an inductor to reduce rise time so fuse blows before such a high current. Add an electronic FET "fuse"?
With boost converter, current will never get higher than what you've pumped into the inductor (at least while boosting to a higher voltage)


What is the 400VDC output feeding? What kind of loads are they?

Just the inputs of an inverter. I assume it is a reprogramming, possibly some hardware modification, of Sunny Boy PV inverter.
Sunny Boy Storage is rated for 9300VA surge, so not a lot of current from 400V battery. (100V to 550V range.)
 
I'm interested in utilizing the SMA Sunny Boy Storage inverter for a battery bank. I understand that for example the LG Resu HV battery is actually a 48v bank with a DC-DC boost converter that is outputting 400v. I'm assuming that this converter is a bidirectional converter, which would then allow for charging of the batteries. The only one I have been able to find is THIS one. At about $4000 per 2Kw, that's a very expensive proposition. I rather like the idea of building a 48v pack and then boosting the voltage, as it seems inherently safer to deal with, but perhaps the only option for DIY is to actually build a HV pack and then use Batrium, REC, Emus or some other BMS capable of dealing with higher voltage. I haven't been able to find any examples of people using this inverter with anything other than a commercially available battery pack.. perhaps someone knows of such an integration.
I'm thinking a few things:
- 1st find out for sure, its bidirectional because the max voltage intake if it has an onboard controller is crucial. This kinda stuff is what limits panels btw.
- Im not a voltage person... tend to focus on amps but ok. Everybody has their on thing.
- clarifying ur statement: appears when I say bank, ur talking about 1 48v battery. Just noted cuz I personally am not a fan of 1 battery setups.
- Im not familiar with that inverter either. I mean like I boost small battery packs but 400v is a wow.

I assume u know how to set this up outputting 400 . U know the drill... boost to meet requirements of next step, diode to regulate, resistors to lower voltage... everything has to do with the amount of current cuz too much = too hot = damage or fire.

Long story short: I would definitely check my specs and do a layout plan on this one 1st. (I tend to have it all in my head lol)
 
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