Rec-Bms has a precharge to automatically pre charge the circuit 11-68 volts with a 4 second delay (programmable 2 to 11 sec delay) for use with a contractor (main relay).
If I was using a contactor with my BMS I would use a toggle switch plus a push buttonI have the same 50-ohm resistor (as seen in mrnatural22 photo )connected in series with a push-button switch. These two are then connected across the terminals (in parallel) of my 100 amp circuit breaker that is in series with the positive lead of my battery.
Before I switch on my breaker, I hold the push button switch for about 5 seconds then let go of the button and switch the breaker on.
I don't ever see any sparks anymore and when testing the resistor current when pushing the button, there is very little and prevent that spark. - It works for me!
What does that cost?Rec-Bms has a precharge to automatically pre charge the circuit 11-68 volts with a 4 second delay (programmable 2 to 11 sec delay) for use with a contractor (main relay).
As you point out, there is not much detail in the description so it is hard to guess what is inside it. My guess is it is a pre-charge through a resister and a bank of FETs that don't turn on till the voltage at the inverter gets high enough.I like that the CSL500 doesn't require remembering to precharge/knowing if the capacitors have dissipated, but I'm curious what the other pros and cons are.
I just looked at that a bit more carefully. It requires a BMS that switches the battery positive rather than ground like the vast majority of FET based BMS so. It would work as is, with an Electrodacus BMS and obviously a Rec-BMS.Rec-Bms has a precharge to automatically pre charge the circuit 11-68 volts with a 4 second delay (programmable 2 to 11 sec delay) for use with a contractor (main relay).
Good points.1) what is the effective resistance when it is 'on'? With the kind of current we put through large inverters, even a tiny resistance would create a lot of heat/energy loss. Judging by the size of the metal case, my guess is there is a significant energy dissipation across it. This also means there will be a voltage drop across it so your inverter will 'see' a lower voltage than what is actually at the battery.
2) What is the reliability of the product?? Anytime you add something to the system, the overall system reliability is impacted by the reliability of what you add. With high current devices such as this, careful design is necessary to have good reliability.
Hello,I just looked at that a bit more carefully. It requires a BMS that switches the battery positive rather than ground like the vast majority of FET based BMS so. It would work as is, with an Electrodacus BMS and obviously a Rec-BMS.
You could use a FET based BMS with the Rec BMS Precharge if you added a relay so the BMS switches battery positive.
I was thinking about how you would combine my circuit with a FET based BMS and came to the realization that my system would also require the BMS to switch the battery positive so that the battery wouldn't supply current out the precharge resistor if the BMS disconnects the battery. I would just add a small solid state relay to my circuity to do this.
The guys at Rec-BMS already figured that out. It makes sense why Rec-BMS didn't do that for their solution. They are selling this as an accessory to their BMS which must switch battery positive. Makes the Rec-BMS less attractive to those wanting to use a cheap FET based BMS to drive a contactor.
I designed my own precharge circuit. It is manual. Press a button, then turn on the battery disconnect.Hello,
Have you been able to run a fet based bms with Rec BMS Precharge + Contactor?
Thank you very much!
can you post a photo? thanks!I designed my own precharge circuit. It is manual. Press a button, then turn on the battery disconnect.
I'm not sure why this has so many problems.I designed my own precharge circuit. It is manual. Press a button, then turn on the battery disconnect.
@HaldorEE is talking about a circuit like this:can you post a photo? thanks!
It was simpler, just a switch and a resistor around the breaker.@HaldorEE is talking about a circuit like this:
View attachment 35647
@Supervstech is talking about a circuit like this:
View attachment 35648
This circuit is documented in this resource:
Inverter Disconnect Switch with Precharge
To get the paper, click on the orange button at the top of this page. This circuit is designed as a disconnect switch that allows the user to pre-charge the inverter capacitors before turning the switch completely on. 26 June 2020 update: At...diysolarforum.com
Correction, its a 10k resistor, can't edit my post.I'm using a 40k ohm resistor continually bridging the contactor, at 51v it only passes about .1millamp and according to the numbers it'll fill a inverters capacitors in about 25 mins but not allow the voltage to rise enough to turn the inverter back on.
40 ohm at 10W is pretty ideal for a 12V system.
I am using an 82 ohm, 25W resistor with my 25.6V battery. And yes I know this is slightly overkill. I even have a heat sink for the resistor. People just don't have any idea hot resistors can get dissipating power.
My experience is that the inverter turns on but immediately goes into an under-voltage state.I wonder about too large a value, allowing inverter enough time that it tries to power up before you close the switch.