charging etiquette - re park feature

[ajdelange]

Although I didn't get an answer as to the battery if I assume that @Luke42 is right (and that certainly seems plausible) and that there are 5 of these packs in series that implies, per the specs on the vendor's sheet, that the discharge cutoff (0% SoC) is 99.4V and that the charge cutoff limit (100% SoC) is 126 V then these 120 V DC/DC converters can potentially charge this pack to 77% SoC. Again, per the specs, the pack's capacity would be 26.5 kWh. Each hour of charging at 2A from each converter at 120 V implies 480 Wh added:. 480/26.5 = 0.0181132 or about 1.8% per hour. Where I live I get 2 hr FES (Full Equivalent Sun) per day in the winter and 5 in the summer so that would mean 3.6 to 9 % charge added. As an experiment i'd say it's absolutely worth a shot but I cannot go so far as to recommend that you undertake it as I don't believe that someone who doesn't know the difference between AC and DC should be playing with electricity - even at 120 V.

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[Crissa]

PWM wastes power when cutting its pulses. That's why an MTTP system is better, as it shifts the voltage state. It handles a higher voltage range, too.

-Crissa

 

[Tinker71]

That would clearly be the minimum risk approach but is such a kluge and so out of the spirit of the endeavor that I didn't even suggest it.


I don't know anything about your converters other that what is in the spec sheet. The spec sheet implies that they can be configured as current sources. You could configure each of them to be a 2 A current source. Then whatever the battery state and whatever the sunlight available they will adjust the PWM to try to push 2 A each into the battery at whatever voltage it is charged to. If the battery is charged to below 120 V the converter will adjust its voltage (by modulating the PWM) to whatever voltage is necessary to push the 2 A. If the battery is charger to a level such that 120 V cannot push 2 A the charger will simply go to the highest voltage it can, 120, and whatever current flows will flow. Clearly if the battery is charged to above 120 V the converter cannot deliver any charge to it.

This makes for a very simple connection. Simply wire each converter to the battery bus through an isolating diode (so that if 1 converter is at 118 V and the other at 117 V the former's current will go to the battery and not the lower voltage converter. These diodes also prevent a battery charged to 124 V from feeding power to the converters at less than 120 V.


As I've indicated in the earlier posts when the battery voltage exceeds the converter voltage no current can flow in either direction because of the diode.

With respect to the battery safety: if the pack open circuit voltage is 120 V at some safe SoC such as 80% this arrangement will never charge it above 80% but it will never hurt it either. If the safety boundary is at some lower voltage you can still configure a safe system by simply setting the converters' voltage limits to that safe voltage.

Now what you really want is a converter that reprograms its output current periodically and stays at whatever current maximizes the output from the panel. I am referring, of course, to one that does MPPT.

Yes but telling an old EE that you have a transformer when you actually have a DC/DC converter surely confuses the hell out of the old guy.

Thanks brother. I will really need to dig for info on my dc converters. They were $19 on Amazon.

 

[Tinker71]

Although I didn't get an answer as to the battery if I assume that @Luke42 is right (and that certainly seems plausible) and that there are 5 of these packs in series that implies, per the specs on the vendor's sheet, that the discharge cutoff (0% SoC) is 99.4V and that the charge cutoff limit (100% SoC) is 126 V then these 120 V DC/DC converters can potentially charge this pack to 77% SoC. Again, per the specs, the pack's capacity would be 26.5 kWh. Each hour of charging at 2A from each converter at 120 V implies 480 Wh added:. 480/26.5 = 0.0181132 or about 1.8% per hour. Where I live I get 2 hr FES (Full Equivalent Sun) per day in the winter and 5 in the summer so that would mean 3.6 to 9 % charge added. As an experiment i'd say it's absolutely worth a shot but I cannot go so far as to recommend that you undertake it as I don't believe that someone who doesn't know the difference between AC and DC should be playing with electricity - even at 120 V.

Really ! I missed an ee term and assumed folks would know that my batteries are dc. I know the difference between ac and dc. I built an electric car albeit with a kit diagram in my garage after work. Btw my panels tilt and I live in Utah.

 

[Crissa]

Really ! I missed an ee term and assumed folks would know that my batteries are dc. I know the difference between ac and dc. I built an electric car albeit with a kit diagram in my garage after work. Btw my panels tilt and I live in Utah.

I would suggest working on building a battery pack from scrapped lithium or NiMHs if you're looking for a project to raise your knowledge of how these systems work. There's kits or at least plans out there now.

-Crissa

 

[ldjessee]

Now You Know (YouTube channel) did a series on making an electric lawn mower that covered a few things about Lithium battery pack creation that I was not aware of, but most of it is pretty basic stuff, so might be less helpful for someone with so much EE knowledge.

 

[ajdelange]

Really ! I missed an ee term and assumed folks would know that my batteries are dc.

My concern is not with other folks.

I know the difference between ac and dc.

I can only judge from what you write. When you write about transformers that are really DC/DC converters it is does not suggest deep knowledge of matters electrical. Unless you completely understand why I suggested what I suggested and why I suggested it I would not undertake the project. You need to understand it at least well enough to be able to determine whether my suggestion was a reasonable one. Maybe I overlooked something? Would you know?

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