Tap 48V battery at 24V leg for shunt trip

I am planning on installing a shunt trip breaker after the Batrium and before the inverter for this Powerwall that I am building. As per Daromer's great video and recommendation it looks like the ABB line of breakers are a good choice to answer this need. However every one of ABB that I have looked require 24V for voltage for the shunt trip and my battery is 48V. Daromer uses a resistor in line when supplying the voltage to the shunt trip from a 48V battery. My question is, couldn't a solution be to just tap the battery at is 7S/24 volt leg for this need? What would be wrong with this solution?

Thanks as always ...

Richard

Nothing wrong with that... done it this way myself..
The short pulse in case of a critical event, will couse no inbalance or so, just d'ont forget a fuse.
As long you d'ont use the center tap to power devices there is no problem.

IF you can tap without any Idle consumption then go for it. Next challenge is to not add more Componenta than needed that can fail. You can use a relay that is triggered by the watchmon engaging the shunt but choose a Good One then.

I use the resistor since its simple but i also have installs with a relay center-tapping

I would be going wit the ABB with internal coil like you have suggested Daniel. If I did set it up this way, why would I need a relay then? Yes I plan on fusing the shunt trip with the recommended fuse of 4A that is shown on the Batrium web site diagram.

If you use the relay on expansion board then its fine but you didnt have the expansion board or did you? Or how do plan to hook up 24v in when the watchmon is powered by 48v?

Currently my plan is to hook up the shunt trip as per this diagram from Batrium:





They do not indicate any relay needed with this diagram ....so what am I missing?

And as I understand this Batrium diagram is for just using the mosfets on the Watchmon 4 to control a negative senseshunt trip breaker

With a 48V battery integrated with a shunt trip breaker that requires 24 volt supply forthe shunt trip, :


1. The positive of the battery connects to the positive supply voltage of the Watchmon4 with a 2A fuse in line. As per this discussion I would connectthe positive side of the trip on the breaker with a 4A fuse in line to the positive leg on the 7S/24 volt leg of the battery.
2. The negative side of the battery connects to the negative ground of the Watchmon 4 and to one side of the negative sense of the trip shunt breaker
3. The other lead from the sense on the trip shunt breaker connects to the input A on the Watchmon 4.
4. The output A on the Watchmon 4 connects to the negative side of the trip on the trip shunt breaker.
5. The load (inverter) is connected through the shunt trip just like any regular breaker

Is this all correct?

Then the software must be set up to determine what causesthe breaker to be tripped?

Thanks,

Richard

daromer said:

If you use the relay on expansion board then its fine but you didnt have the expansion board or did you? Or how do plan to hook up 24v in when the watchmon is powered by 48v?

Click to expand...

@Headrc does not have the expansion board. @Headrc - what @Daromer is saying (I think) is that if you use the Watchmon4 (only) then the shunt-trip coil must be same voltage as you are running into the Watchmon4. If you have expansion board, then Watchmon vs Expansioncircuits can be different voltages.Typically witha 48v battery you are running 48v into theWatchmon4 and so you can't use Watchmon4shunt-trip that needs 24v (it would have to be a 48v variety).

However, it seems like you can center tap your battery for 24v and power the Watchmon4 with 24v and then use 24v coil on shunt-trip. I don't think the 'load' of powering the Watchmon4 from center-taping your 48v battery (assuming its big enough)will significantly throw the battery off. Maybe someone can confirm that this is OK.

Alternately (and maybe preferred) you can buy a DC (48v) to DC (24v) converter and draw 48v from the fullbattery but power the Watchmon4 + Shunt-trip coil with 24v. This 'may' be required anyway if the ABB shunt-trip requires an actual/steady 24vinstead of voltage range of battery hi/low - e.g. if battery was really low like 21v it might not be enough to trip the shunt.

Thanks Offgrid ...hopefully Daromer and others can give clarification on this.

Do not center tap to Power wm. Its enough to cuse inblance

Ok I will go on that advice and use a resistor as previously advised. But with all that are all systems go ...and I do not need an additional relay since I do not have the expansion board?

Advice to avoid center tap is clear and I agree... but I been wondering from a theoretical/electrical standpoint.

Can you 'double tap' a 14s battery - e.g. run a neg/pos from packs 1&7 and then 7&14 and then hook them together (parallel them) to get 24v that would draw a 'balanced' load? - while at the same time the main 48v outptu is doing its thing.

Now that is an interesting idea.

No you cannot. Draw that up on a paper and you see why... Or try it but dont forget to video it so we can see the reaction when it goes boom

OffGridInTheCity said:

Advice to avoid center tap is clear and I agree... but I been wondering from a theoretical/electrical standpoint.

Can you 'double tap' a 14s battery - e.g. run a neg/pos from packs 1&7 and then 7&14 and then hook them together (parallel them) to get 24v that would draw a 'balanced' load? - while at the same time the main 48v outptu is doing its thing.

Click to expand...

Uhhhhh :boom!:

*IF* you do this, make sure to include some heavy duty diodes "with" fuses on each leg.

But still video it so you can show us the results

Yikes - dead short. Stupid question!!!