Timer relay delay for 48v system

[cinergi]

I'm having a hard time finding solutions that can handle 48v control and 48v switching that would allow me to create a pre-charge circuit for my 48v bank. The Orion BMS would act as a trigger (max 175ma but I want to stay well under that) which would enable a small relay with a resistor and in parallel would start a timer that would eventually activate the large 48vdc contactor. In theory I could tap the 12th cell of the battery to get 12v control but I really don't like the idea of pulling constant power from the middle of the bank. Some of the boards I see on e.g. Amazon pull 30ma... and none of them go above 30vdc for the controlled load. For the same reason, I don't want the contactor coil to be anything other than 48vdc. If I were to convert 48 to 12 or 24 for driving the timer board, I'd want a cheap but very reliable converter that doesn't use power at rest (since this is my battery protection circuit). And then I'd still have to find a solution that can handle driving a 48vdc coil.

What are others doing? Thoughts?

Thanks!

 

[BiduleOhm]

Why not just use a RC timer on the relay's coil?

Easy, available up in the hundreds of volts if you want, reliable, simple, ...

 

[cinergi]

Why not just use a RC timer on the relay's coil?

Easy, available up in the hundreds of volts if you want, reliable, simple, ...

You mean something like: https://electronics.stackexchange.com/questions/315174/creating-a-timer-in-an-rc-circuit ?

Unless you had something else in mind, I'm not comfortable with slowly raising the voltage until the relay latches for a couple of reasons, the most important of which is that I want the capacitors at a minimum of 50v before throwing the main contactor (dual 5k inverters). The first relay would engage way before that. I used to do simple circuits on breadboards a LONG time ago in school and if I had to (e.g. 555 timer), I could do it, but I really don't want to. I might be more inclined if Radio Shack still existed Paying $8 to Mouser every time I need a 50 cent part ... lol

Sadly I've tried to contact REC BMS for their delay box and they never get back to me.

 

[BiduleOhm]

You mean something like: https://electronics.stackexchange.com/questions/315174/creating-a-timer-in-an-rc-circuit ?

Unless you had something else in mind, I'm not comfortable with slowly raising the voltage until the relay latches for a couple of reasons, the most important of which is that I want the capacitors at a minimum of 50v before throwing the main contactor (dual 5k inverters). The first relay would engage way before that.

Yep.

Ok, then you can add a zener and a transistor to have a clean transition instead of ramp, and to choose exactly the voltage you want

NB: if you want to avoid any problem on the relay due to a slow ramp you can use its output to feed the the coil, that way it will latch cleanly.

I used to do simple circuits on breadboards a LONG time ago in school and if I had to (e.g. 555 timer), I could do it, but I really don't want to. I might be more inclined if Radio Shack still existed Paying $8 to Mouser every time I need a 50 cent part ... lol

There's also Digikey and Farnell, and I know Farnell is free shipping for orders above 30 €.

Other thing is to wait to have more components to order for other projects but if you don't do that kind of projects often it doesn't work of course ^^

You can also order on general online marketplaces like amazon, ebay, etc... but the quality isn't guaranteed (however, in this particular case you don't need expensive and/or rare and/or complex components so it shouldn't be a problem).

 

[nebster]

If you just want to buy something, have a look at Crouzet controls, or any other industrial programmable timer. Something like MUR3 will do what you want, for $$, at any VDC you care to provide it.

You know, though, that you don’t need automated precharge. You’re over-engineering.

 

[cinergi]

Maybe. I've blown 2 300 Amp Class T fuses because of inrush - and it was due to automated shutdowns and turnons due to BMS control. With Orion and CANBUS interface with Victron, I've managed to get to the point where that contactor doesn't shut down anymore ... but it could easily happen while I'm not around to catch it.

 

[BiduleOhm]

In the mean time just connect a resistor across the contactor to avoid the fuse blowing problem

A few dozens Ohms should be fine, just be careful about its power rating.

 

[cinergi]

In the mean time just connect a resistor across the contactor to avoid the fuse blowing problem

A few dozens Ohms should be fine, just be careful about its power rating.

Yes I have that in place for now. 50 ohm 100 watt IIRC.

 

[nebster]

Maybe. I've blown 2 300 Amp Class T fuses because of inrush - and it was due to automated shutdowns and turnons due to BMS control. With Orion and CANBUS interface with Victron, I've managed to get to the point where that contactor doesn't shut down anymore ... but it could easily happen while I'm not around to catch it.

I can think of no reason I’d want a BMS to automatically reapply a battery after a disconnect in a single-channel circuit. Even on the bench, I would want a configuration that never does that.

If you’re saying you need a safety net until you get your BMS programmed properly... okay, sure. But in production you should never have to deal with this.

I’ve given you a sku that I think is an answer to your problem, but for the benefit of other readers if not yourself, I just worry that you’re asking the wrong question. In a shutdown — which should be rare, if it ever happens at all — we want the reconnect to be attended, because something went very wrong. And if we’re there to attend to it, well we can just use a lightbulb (or your power resistor, but lightbulbs are more fun, because they show you when it’s done charging and warm the heart).

 

[cinergi]

That's definitely something to noodle on. I think in the case of HVDC, it makes sense. in the case of LVDC, it may just be a lack of sunshine In that case I really should have a separate port configuration that allows an LVDC disconnect of the inverter/charger but still allows solar to charge the batteries and then the inverter/charger can reconnect if/when there's sufficient voltage (so the food in my fridge doesn't go bad, for example).

I have been ruminating about whether to have separate port ... if I go with common port, then I think you're right ... attendeded reconnect. I need to research if I can even prevent automatic reconnect (I would think so, but I'm not sure)... as I think about it, that's really what's been plaguing me ... I'd need it to shut down and stay shut down.

Also, LOL on the lightbulb comment. I did think about doing that

 

[nebster]

It's pretty hard to do dual-channel BMS with an inverter-charger combination unit, since there is only one pair of wires coming out of it. You really have to step up to digital control (CAN or whatever) where the BMS instructs the unit(s) to stop or start charging and/or discharging.

In those cases, the relay is not disconnecting (it remains as an emergency last-ditch method), and so the caps will stay charged.

You can have your DC and AC loads shut down programmatically even without that fancy approach, though, and you may want to. That way you don't have LVDC except in a protracted energy shortfall, like maybe days or weeks of nothingness.

Are you going to have a generator available on demand? For a lot of mobile setups, that is the fallback plan when PV can't deliver. I guess I was assuming with your large project that you have one employed.

 

[cinergi]

I do have the Orion speaking CANBUS to the Victron system so the contactor is indeed a secondary shutoff. It shouldn't happen. Additionally, I'm researching the apparent ability for me to further control the Quattro's through auxiliary signals to (because, for example, I can't properly float the battery bank while it's under CANBUS control unless I also use the Orion to trigger an auxiliary signal).

The separate port idea is for solar charging (independent of the Quattro's). I know the Quattro's must be on a common port.

I do tend to agree with your comments ... I think I'm gun-shy because I've had contactor shutdowns but that was largely due to tuning errors. Once tuned and deployed, I think you're right -- that contactor should never turn off for all practical purposes.

Good question on the generator, and TBH I'm still debating an onboard unit (because it's incredibly expensive for this particular 5th wheel and I'm not impressed with its sound specs). At a minimum I'll have a portable attached but I don't know that it will properly serve as an automatic standby if, e.g., the batteries go under 20%. That's something I won't know until I get some field experience living in the RV.

At the end of the day it looks like the REC BMS precharge delay would work for around $100 .. but I'm not convinced I need it.

The design is going through a LOT of revisions and thinking as I get experience with it. I never thought I'd have a CANBUS controlled battery when I first put this together!

Thanks for your input!

 

[nebster]

I do have the Orion speaking CANBUS to the Victron system so the contactor is indeed a secondary shutoff. It shouldn't happen. Additionally, I'm researching the apparent ability for me to further control the Quattro's through auxiliary signals to (because, for example, I can't properly float the battery bank while it's under CANBUS control unless I also use the Orion to trigger an auxiliary signal).

Oh, hmm, that's interesting. So the CAN protocol doesn't include a way for the BMS to tell Victron to switch to Float? You just get charge current as the parameter, and so the Quattro holds the higher CV voltage? If so, that doesn't sound ideal.

The separate port idea is for solar charging (independent of the Quattro's). I know the Quattro's must be on a common port.

Coupled with the possibility that you might not have a permanently-mounted generator, I now understand why you might anticipate a system shutdown at some point.

I'd still hope you'll be living in the RV and managing it mostly, and when you're not you'd be conserving power, but... enough shade and refrigerator-running and you might still manage to take out a big battery like you're building.

I do tend to agree with your comments ... I think I'm gun-shy because I've had contactor shutdowns but that was largely due to tuning errors. Once tuned and deployed, I think you're right -- that contactor should never turn off for all practical purposes.

Good question on the generator, and TBH I'm still debating an onboard unit (because it's incredibly expensive for this particular 5th wheel and I'm not impressed with its sound specs). At a minimum I'll have a portable attached but I don't know that it will properly serve as an automatic standby if, e.g., the batteries go under 20%. That's something I won't know until I get some field experience living in the RV.

I know people get electronic start kits for those portable ones, so I imagine it's possible. It might be finicky to have to set it up and tear it down regularly, though. Maybe something that would make sense if you're in one place for longer periods, though.

GL, keep at it!

 

[cinergi]

Oh, hmm, that's interesting. So the CAN protocol doesn't include a way for the BMS to tell Victron to switch to Float? You just get charge current as the parameter, and so the Quattro holds the higher CV voltage? If so, that doesn't sound ideal.

Yeah it's a bizarre limitation. It does bulk until it hits max voltage and then just sits at max voltage (absorb) forever. So right now I can only charge to 54.4. This is all of the stuff I've been learning the hard way over the past week ... There are other nuances which I haven't mentioned yet and now finally understand how the Orion works and I recently learned about this Victron 2-signal BMS thing which might get me what I need in order to achieve a proper 3-stage charge. Once I get a config I'm happy with, I'll probably need to do a dedicated Orion & Victron how-to video.

I'd still hope you'll be living in the RV and managing it mostly, and when you're not you'd be conserving power, but... enough shade and refrigerator-running and you might still manage to take out a big battery like you're building.

You're probably right that I'm over-thinking/preparing... while I'm boondocking, I'm not likely to be away from the RV for more than a day...

I know people get electronic start kits for those portable ones, so I imagine it's possible. It might be finicky to have to set it up and tear it down regularly, though. Maybe something that would make sense if you're in one place for longer periods, though.

Since I work during the week I tend not to move often (public lands often require moving every 2 weeks); propane connection to the RV, so hopefully not too bad. I don't even know yet if the generator will handle the load, should that need arise.

GL, keep at it!

Thanks! It's turned into a fun hobby and keeps me busy (especially important these days)!