prime the caps in my inverter by connecting it directly to my converter

[RCinFLA]

I was examing BMS's on ebay and came across a 16s 320 A with Bluetooth data link that had some interesting pictures.

It has 7 back to back series pass pairs on top side and another 7 back to back pairs on backside for 14 total pairs in parallel.

The interesting thing I noticed is an extra single MOSFET with series resistor at end of series high current switch MOSFET's going to Drain center bus.

Since this extra MOSFET is on the battery connection side it is intended for softstart surge current limiting. One of the parallel resistors is 1.0 ohm but it is hard to make out the multiplier color on second parallel resistor, either 5 ohm or 0.5 ohm..

So this extra MOSFET fires up a few hundred microseconds before turning on the 14 parallel high current pairs providing a maximum 50-90 amp softstart current to charge inverter capacitor.

First unit I have seen with softstarter. It also looks to have a temp sensor on a flex over the series pass MOSFETS.

 

[FilterGuy]

That BMS is the ANT BMS. An 8S version of it was reviewed by @Will Prowse quite a while back. I installed an 8S ANT bms at a cabin a few weeks ago. I can't say I have a lot of history with it but it seems to work pretty well.

Good catch on the pre-charge. I think you are correct. When I was first setting it up, I had the battery type wrong and while I was futzing around trying to figure it out I got an error message that said something about the pre-charge current was too high. That made me wonder if it had pre-charge built in but by the time I figured out I had the battery type wrong and corrected it, I forgot about the pre-charge and never followed up.

My main gripe with the ANT BMS is how to turn it on after you set it up. There are two options:

1) Apply a charge to the batteries.
2) Apply 3.2-5 Volts to the on/off wires.

@Will Prowse also found that the two on/off wires need to shorted together after you apply the voltage.

I ended putting in a DPDT switch that will connect the two wires to one of the cells in one position and short the two wires together in the other position.

 

[Mex Rider]

BTW: It may not be as bad as I make it sound. The most likely reason for the BMS to shut off discharge is if the battery or cell is too low. Many (Most?) BMS's will not turn back on till the battery gets charged to an acceptable level. I have not played with it, but I suspect whatever is charging the battery enough to turn the BMS back on will also charge the inverter capacitors. Consequently, there should not be a surge when the BMS turns on.

But doesn't the inverter remain "off" until the set point is reached and then turns "on", allowing a fresh inrush to the caps or is the circuit of the inverter receiving a trickle say from the PV while the batteries are charging? And all of this is to say no human intervention when the inverter had a low voltage shut down, which of course is a real possibility.

 

[FilterGuy]

The capacitors are always on the DC input side of the switch and control circuit. Consequently, the capacitors will charge even if the inverter has turned itself off. If the low voltage cut-out-recovery of the inverter is higher than the low voltage cut-out-recovery of the BMS things will turn back on in a controlled manor and not have an in-rush.

Starting from the BMS having cut out, (and therefor the Inverter also cut out).
1) A charge source (such as PV ) turns on and starts charging the battery.
At this point the voltate is still too low for both the BMS and the Inverter. However, the batteries and inverter capacitors start charging. The inverter might start drawing some small current to run it's controlls, but the invert function will still be off because the voltage is below the low voltage cut-out-recovery.

2) The batteries charge enough for the BMS to turn on.
At this point the voltage is still too low to turn on the inverter function. The batteries and Inverter Capacitors are still charging.

3) Eventually the batteries (and capacitors) are at a high enough voltage to turn the inverter function back on.

Note: Once the inverter function turns back on, if there is a large load on the inverter, it might quickly drain the battery and cut back out. This is why it is a good idea to set the 'low-voltage-recovery' voltage of the inverter somewhat higher than the low-voltage-cut-off voltage (if the inverter allows it)

Warning: I was recently made aware that on Cotek inverters, if you connect the batteries while the inverter switch is in the on position, it can damage the inverter. However, from experience I know that if you pre-charge the capacitors with the inverter turned on, and then connect the batteries it works ok. It only seems to damage the inverter if there is a large in-rush. I happen to know that Cotek uses a lot of small fuses in parallel rather than one large fuse. I *suspect* the inrush blows one of the small fuses. With the scenario I describe above, there would never be a large inrush so this should not be a problem. I don't know if this applies to other brand inverters.

 

[Mex Rider]

[/QUOTE]

 

[Mex Rider]

But doesn't the inverter remain "off" until the set point is reached and then turns "on", allowing a fresh inrush to the caps or is the circuit of the inverter receiving a trickle say from the PV while the batteries are charging? And all of this is to say no human intervention when the inverter had a low voltage shut down, which of course is a real possibility.

Obviously out in left field...sorry

 

[theoldwizard1]

Watch this video

How to make a Softstarter and why it is sometimes mandatory to use!​