Precharge active at the same time as main switch

[jontm]

Hi!

Long story short, my BMS did not have precharge functionality as my seller told me, so i have to design my own.
I have a fairly large Victron Quattro 48 V 10000 VA and therefore absolutely need a precharge. Yes manual precharge would be possible, but in the event that the BMS shut down the contactors and restart automatically or somebody forget to turn on the precharge i do not want to destroy my contactors

I am designing a pretty simple delay circuit for the contactor to allow the precharge to charge the input capacitor though a power resistor before engaging the main contactor.
However it is much simpler for me to just have the precharge switch not turn off when the main contactor go active. Then i can just wire the precharge switch directly to the contactor output of the BMS and the contactor though a delay circuit. Having the precharge turn off when the main contactor go on, adds complexity to the design.
I do not see any immediate reason why the precharge cannot be active while the main contactor is active. I mean, it would just be like 100 Ohm in parallel to the contactor when it is on. It will turn off at the same time as the contactor.

Any opinions ? Are there any reason for the precharge having to be turned off when the main contactor is on ?

 

[SparkyJJO]

Which BMS, out of curiosity?

A resistor in parallel with what amounts to be a straight wire will hurt nothing. You'll have basically no voltage potential across it anyway, so it won't even waste power.

 

[acdoctor]

I see no problem with the plan but if your contactor is like most I have experience with. They close at around 60 to 75% voltage. ( 48 volt system it would close around 30 to 40 volts). A test could confirm this. If so you could connect coil of contactor in series, when system voltage comes up to around 35 volts contacts would close. Then you won’t need the timing circuit. This looks good in my mind but I have not put it on paper. What is the coil resistance and what size resistor are you planning to use? Does anyone see a problem with this?

 

[jontm]

Which BMS, out of curiosity?

A resistor in parallel with what amounts to be a straight wire will hurt nothing. You'll have basically no voltage potential across it anyway, so it won't even waste power.

That is my thinking as well. I plan to just use a simple SSR with a 100 Ohm power resistor connected in parallel over the relay. The 12 V signal going to the relay connected directly to the SSR control input and a simple delay turn on delay circuit for the main relay. So that every time the BMS output 12 V to turn the relay on, the SSR will turn on immediately, but the main relay will be delayed by maybe something like 5 seconds.

I am probably one of the very few with the JK-B2A25S60p. Will probably make a separate thread on it as very little information is available on it and I have some info to share regarding this that people should be aware of before ordering

I see no problem with the plan but if your contactor is like most I have experience with. They close at around 60 to 75% voltage. ( 48 volt system it would close around 30 to 40 volts). A test could confirm this. If so you could connect coil of contactor in series, when system voltage comes up to around 35 volts contacts would close. Then you won’t need the timing circuit. This looks good in my mind but I have not put it on paper. What is the coil resistance and what size resistor are you planning to use? Does anyone see a problem with this?

The JK-B2A25S60p have 12 V relay outputs so this would not really work. This is good as you can use the cheap Kilovac EV200 12 V coil relays that are all over AliExpress right now. 48 V relays are quite a bit more expensive.

 

[yaq]

Question : pourquoi ne pas simplement mettre une résistance en parallèle sur les contacts du relais et insérer un interrupteur en série si vous souhaitez isoler complètement la batterie ?