Electronics > Power/Renewable Energy/EV's

"Simple" way to prevent over-voltage cutoff on battery powered inverter

<< < (3/3)

Ziggo:

--- Quote from: Faringdon on November 12, 2022, 05:58:32 pm ---You can buy step down modules from murata, vicorpower etc.....

--- End quote ---

The issues here are:
  1. Cost - I want something for around $50, $100 max.
  2. Complexity / Time - I don't have the expertise needed to do this in a reasonable amount of time (a few hours).

Ziggo:

--- Quote from: Siwastaja on November 12, 2022, 01:42:19 pm ---Is it possible to just terminate charging early? Just charge to 60V, which is 4.0V/cell, roughly 80% SoC. Good for battery life, too. This would be simplest, by far.

--- End quote ---

I have considered doing this, but the main issue is that I would need to babysit the battery charging and pull it off at the right time. Or, use some other load to discharge the battery down to a usable level if it gets fully charged.

I finally received my Mean Well inverter and tested it with my battery (a 60V, 8.0Ah battery from Greenworks - I already have 4 of these). The battery gets to 63V at full charge and the inverter cuts out above 59V.

So, my plan at this time is to use this https://www.amazon.com/gp/product/B07YTVK1JK/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1 low/high voltage disconnect relay driving a 40A 100V solid state relay (that I already had). When the relay is open, there will be a series of power diodes (which I also already have) to do the 4V voltage drop. When the voltage drops enough and the relay is closed, the diode bank will be shorted out.

I still need to wait a week or two for the disconnect relay to get here. It's not a very elegant solution, but I think it will work OK. The battery voltage drops pretty quickly under load so the diodes will only be in line when the battery is full and the load is light.

M0HZH:
A workaround which will add another point of failure, complexity and reduce efficiency. You also don't want to always be very close to the absolute maximum voltage rating of the inverter, for long-term reliability (or nuisance overvoltage cutoffs).

Sounds like the inverter is most likely designed with 48V operation in mind, isn't it better to find a 13S battery (which are quite common)?

2N2222A:
I liked the MOSFET body diode idea. How about 6 5A diodes in series. When the current exceeds 5A a relay closes or a MOSFET turns on to bypass the diodes. They could be 10A diodes in a TO-220 package along with the MOSFET. All on the same heat sink.

Magnethicc:

--- Quote from: Siwastaja on November 12, 2022, 01:42:19 pm ---Is it possible to just terminate charging early? Just charge to 60V, which is 4.0V/cell, roughly 80% SoC. Good for battery life, too. This would be simplest, by far.

--- End quote ---
By far the easiest solution.
OP suggestion is to put diodes in series to drop the voltage but will dissipate ~100W which will need to be dissipated with considerable heatsink.

It is much easier to measure the voltage of the battery (resistor divider) and disconnect the charging station when the measured voltage gets to a reference value.
OP already have a relay so just connect the output of the charging station to the relay. when measured voltage reaches to a set reference value then disconnect the relay.
There is no need to babysit the charging station.

The input voltage to the control circuit can be taken from a buck converter from the charging station/battery or use high voltage op-amps and take the input straight from the charging station/battery.
The current to the relay can be taken from the charging station/battery through a BJT and a current limiting resistor.

Navigation

[0] Message Index

[*] Previous page