Using Blue Sea 187-Series Circuit Breaker/Switch instead of a battery switch

[robepa]

I'm putting together a power system for my Smittybilt Scout Trailer, after putting together initial layout I noticed that Blue Sea says that the 187-Series Circuit Breaker can be used as a switch as well. Using the simpler is better theory of things, would there be any issue with putting one on each battery and then not having a battery switch? I am planning on 2 group 31 AGM batteries, no solar or inverter. This is my first power system, feel free to make suggestions/corrections to the attached system diagram.
Cheers

 

[restorationrides]

I'm putting together a power system for my Smittybilt Scout Trailer, after putting together initial layout I noticed that Blue Sea says that the 187-Series Circuit Breaker can be used as a switch as well. Using the simpler is better theory of things, would there be any issue with putting one on each battery and then not having a battery switch? I am planning on 2 group 31 AGM batteries, no solar or inverter. This is my first power system, feel free to make suggestions/corrections to the attached system diagram.
Cheers

It appears that you still have some drawing to do on this diagram...?

The AC power seems to be connected to the DC power bus.

Your batteries are connected together in series (24v)...is that what you intended? The (-) side of the second battery is not connected.

The second battery is not part of the load equation.

The circuit breaker on the left side of the diagram is correctly installed between the battery and the load.

The circuit breaker on the right side bypasses the battery and is connected directly to the load from the charger. You might check the specs, but most battery chargers have built-in circuit breakers for short circuit conditions so that would just be redundant.

The ground (-) sides of the circuits are mostly missing.

The 187 series circuit breakers that you mentioned are not called out in your drawing (unless they are the two 200amp circuit breakers that are showing). If so, you list the circuit breaker capacity at 200 amps, but the largest of those 187 series is only good for 90 amps continuous...?

Regarding the larger question of whether or not those 187 series circuit breakers could be suitable as switches (too) and avoid having a separate battery switch... I would have to say a qualified YES.

The caveat is that you should to place the two switches in close proximity to each other. That way you'll be sure to have selected the correct combination of batteries for your particular needs at the moment. From that set up, you can pick battery 1 or battery 2 or both battery 1 AND battery 2 combined into the load.

Regards,
RestorationRides

Sent from my REVVLPLUS C3701A using Tapatalk

 

[john61ct]

Yes, but. . .

Only very high quality CBs should be used as switches used frequently.

CBs sized large enough for (dis)charging a big bank are **much** more expensive than the equivalent fuses.

With CBs you need to pay attention to the time-delay ratings. Accidentally shorting across the main +/- posts can melt a crowbar pretty quickly, you definitely want fast action at that location.

 

[robepa]

It appears that you still have some drawing to do on this diagram...?

The AC power seems to be connected to the DC power bus.

Your batteries are connected together in series (24v)...is that what you intended? The (-) side of the second battery is not connected.

The second battery is not part of the load equation.

The circuit breaker on the left side of the diagram is correctly installed between the battery and the load.

The circuit breaker on the right side bypasses the battery and is connected directly to the load from the charger. You might check the specs, but most battery chargers have built-in circuit breakers for short circuit conditions so that would just be redundant.

The ground (-) sides of the circuits are mostly missing.

The 187 series circuit breakers that you mentioned are not called out in your drawing (unless they are the two 200amp circuit breakers that are showing). If so, you list the circuit breaker capacity at 200 amps, but the largest of those 187 series is only good for 90 amps continuous...?

Regarding the larger question of whether or not those 187 series circuit breakers could be suitable as switches (too) and avoid having a separate battery switch... I would have to say a qualified YES.

The caveat is that you should to place the two switches in close proximity to each other. That way you'll be sure to have selected the correct combination of batteries for your particular needs at the moment. From that set up, you can pick battery 1 or battery 2 or both battery 1 AND battery 2 combined into the load.

Regards,
RestorationRides

Sent from my REVVLPLUS C3701A using Tapatalk

Thanks for catching those errors and the details
- My intent is to have the AC power connected to the battery charger and the 2nd power source on the DC frig so it will auto switch when on shore power so we can load the frig the day before we roll out, I can see how in the diagram it looks like the AC power is going to the DC bower bus.
- Thanks for catching the error on the batteries in serial not parallel, that was a copy and paste error, new diagram is corrected with them in parellel.
- Likewise with the 2nd battery not being connected, that is updated.
- I have left the grounds off, i need to find/make a Visio GND symbol. I added ground "tails" that can be assumed to be connected.
- Yes, the 200A breakers are intended to be Blue Sea 187 series, I don't see a continuous load rating on their specs, they do say in one of their breaker videos they recommend that the continuous load not be more than 80% of the rated. Summing everything up I'm at 100 amps ish.

 

[robepa]

Yes, but. . .

Only very high quality CBs should be used as switches used frequently.

CBs sized large enough for (dis)charging a big bank are **much** more expensive than the equivalent fuses.

With CBs you need to pay attention to the time-delay ratings. Accidentally shorting across the main +/- posts can melt a crowbar pretty quickly, you definitely want fast action at that location.

Good points, my boating friends speak highly of Blue Sea Systems. My thought also was if everything was on and drawing power (not a likely case) it would be 100A total load so having 50% headroom in the worst case would help. A dead short with the battery wires would pull way over 200A and trip the breaker.

 

[john61ct]

Yes Blue Sea is da bomb for DC electrics on land too.

http://shop.pkys.com/Blue-Sea-5005-ANL-Fuse-Block-for-Fuses-35-300-Amp_p_1624.html

http://shop.pkys.com/Blue-Sea-9004e-ON-OFF-Battery-Switch-with-AFD_p_1952.html

 

[DaveInDenver]

drawing power (not a likely case) it would be 100A total load so having 50% headroom in the worst case would help. A dead short with the battery wires would pull way over 200A and trip the breaker.

Circuit interruption, regardless breakers or fuses, are sized to protect the cabling. So where you're showing the Blue Sea 200 A breakers wiring will need to be sized to carry that current for the time the breaker will hold it. You need to look at the time-current curve for it (every breaker or fuses has this).



The popular misconception is an interrupt device rating is where it will open. That is wrong. The rating is what the device will hold for an indefinite (essentially forever) period.

A 200 A breaker carries 200 amps

The point where it will break is somewhere above 100% and for some time less than infinity. In the curve you'll see at 500 seconds it'll take between 110% and 130% of rating. It starts to get quicker as current goes up. At 50 seconds the range looks to be about 125 % to 150% (you're at 300 amps now for almost a minute worst case). At 10 second it will take between 200% and 300% of rating (400 to 600 amps) to break.

What this means is you need a cable between the breaker and the 12-position fuse block that can handle this current for the time you expect. That's going to be a 2 AWG cable with 105 ºC insulation. That's not realistic and unnecessary. Size the breaker appropriately, it just needs to hold 100 amps indefinitely so pick a 100 A rated one. You can reduce the wire to more like 8 or 6 AWG. Since you should be running both out and back this is easier to take on the budget and less difficult to route.

I'd probably do 6 AWG personally, maybe 4 AWG if you're flush with money. I personally ran 8 AWG using a 60 A fuse (the Bussman MRBF type) to feed a remote fuse panel in the bed of my truck. But I'm only running a fridge and a single light so voltage drop isn't nearly the concern you'll have with that many loads.

 

[robepa]

Circuit interruption, regardless breakers or fuses, are sized to protect the cabling. So where you're showing the Blue Sea 200 A breakers wiring will need to be sized to carry that current for the time the breaker will hold it. You need to look at the time-current curve for it (every breaker or fuses has this).

View attachment 448676

The popular misconception is an interrupt device rating is where it will open. That is wrong. The rating is what the device will hold for an indefinite (essentially forever) period.

A 200 A breaker carries 200 amps

The point where it will break is somewhere above 100% and for some time less than infinity. In the curve you'll see at 500 seconds it'll take between 110% and 130% of rating. It starts to get quicker as current goes up. At 50 seconds the range looks to be about 125 % to 150% (you're at 300 amps now for almost a minute worst case). At 10 second it will take between 200% and 300% of rating (400 to 600 amps) to break.

What this means is you need a cable between the breaker and the 12-position fuse block that can handle this current for the time you expect. That's going to be a 2 AWG cable with 105 ºC insulation. That's not realistic and unnecessary. Size the breaker appropriately, it just needs to hold 100 amps indefinitely so pick a 100 A rated one. You can reduce the wire to more like 8 or 6 AWG. Since you should be running both out and back this is easier to take on the budget and less difficult to route.

Thanks, I'm planning on 2 AWG, as mentioned I don't need it for the current loads but I don't want to have to redo if i add an inverter or the like. As far as going to a 100A breaker, Blue Sea recommends 80% of the rated so maybe a 125-150A. Is there a down side to over sizing the breakers as long as the wire will support it?

 

[DaveInDenver]

Thanks, I'm planning on 2 AWG, as mentioned I don't need it for the current loads but I don't want to have to redo if i add an inverter or the like. As far as going to a 100A breaker, Blue Sea recommends 80% of the rated so maybe a 125-150A. Is there a down side to over sizing the breakers as long as the wire will support it?

No downside as long as the OCP device is the correct size or less than the capacity of the wire it's protecting. If you're pulling 2 AWG for future you can put a 200 A or smaller and since it's not cheap I would just use the right size now, too. You'll use the fuse block to protect branches, the 187 is only there to protect the battery to fuse block feed. Each device will have a fuse or breaker to protect itself internally, so the fuses in the block are similarly sized based on the wire you use.

Is Blue Sea recommending 80% nominal for holding or 80% of trip current?

I'd personally not de-rate, protection and wire sizing is based on ambient temperature. What I mean is as the environmental temperature goes up the current required to open a fuse or breaker will go down. The element doesn't know or care why the temperature is rising it just knows it's reached a high enough temperature. That's to say that if you put a breaker in your oven at home it would open up with zero current flowing through it. The flip side of this is when temperature goes down the current required to trip will go up.

If you put 100 amps through a breaker designed to hold 100 amps at room temperature (say 25 ºC ) and put it on a boat that's 40 ºC you've in essence consumed 15 ºC of trip margin and it might actually trip at 90 amps or whatever. The problem is the cable also is in this environment presumably and the insulation on it doesn't care how it got warm enough, it just knows it's reached 105 ºC (or whatever) and will start melting.

So I suspect the Blue Sea recommendation is to give yourself 20% margin in expected holding current so as to prevent nuisance trips. If you use a 125 A breaker to hold 100 A you risk not really protecting the wire unless you also upsize it or use higher temp insulation to gain margin at higher ambient temperature. IOW, expect to use 80 A on a system sized for 100 A or size everything for 125 A as your load so that at high temp you won't trip using 100 A in the Bahamas.

 

[dwh]

Go to a 30a charger and you'll have the 10a for the fridge and 20a to charge the battery and you won't need to switch the fridge to AC ever.

 

[DaveInDenver]

Fwiw, 80% of ”maximum” is widely accepted over many industries as a continious load on devices and conductors.
It provides good safety margin & minimise nusiance tripping.

Meaning you build a 100 A circuit to carry 80 A load not that you use 125 A breaker on a 100 A sized circuit. It's nuanced, I know I confused the question. You always match the OCP to cable size and you select the breaker and cable to carry 80% of their maximum.

 

[john61ct]

Yes not much point putting in CP sized smaller than the wire needs.

 

[robepa]

Here is what I settled on, I have the last parts of the system coming in today. Install on my trailer starts tonight! I still need to decide on battery monitor system, what do people like? Let me know if you see any problems with the diagram below, the only thing not listed is a chassis ground from one of the bus bars.

 

[luthj]

If you want optimum life from those lithium batteries, make sure to avoid float charging... That charger you have selected doesn't have the option to disable float charging, and leaving it plugged in for extended periods will accelerate degradation of the batteries. I would also strongly suggest choosing the lower voltage options on that charger (14.1V). However that setting comes with a higher float voltage, which becomes a problem when left plugged in.

It is hard to tell from the documentation, but that charger may hold the absorb (14.1-14.7V) voltage for some time after reaching it. That is good for lead, but has negative effects on lithium. All your doing at that point is putting unneeded stress on the cells, and making the BMS work hard.


Also, you need a way to disconnect your charger from the inverter. Otherwise the charger will power itself from your inverter when on battery power, making a discharge loop.

 

[Bayou Boy]

The above is correct about Lithium batteries. Every manufacturer I have seen recommends storage at somewhere around 50% charge and then only charging right before use. Exactly the opposite of lead acid where you want to bring back up to 100% ASAP.