# Charge controller output circuit breaker rating question

Options
Solar Expert Posts: 428 ✭✭
Looking for a formula to determine circuit breaker rating from the charge controller to the battery bank.

Thanks

Dennis

• Banned Posts: 17,615 ✭✭✭
Options
Re: Charge controller output circuit breaker rating question
verdigo wrote: »
Looking for a formula to determine circuit breaker rating from the charge controller to the battery bank.

Thanks

Dennis

What is the output current of the charge controller?
Wire size has to be able to handle at least that, and then the breaker is sized according to the wire's capacity.
• Solar Expert Posts: 428 ✭✭
Options
Re: Charge controller output circuit breaker rating question

Its a Classic 150 so max is 86 amps at 48 volts , and the wire will be maybe 2' of 1/0, so a 100 amp breaker would work? I would have thought it would have something to do with the battery bank capacity, and max charge rate.
• Banned Posts: 17,615 ✭✭✭
Options
Re: Charge controller output circuit breaker rating question
verdigo wrote: »
Its a Classic 150 so max is 86 amps at 48 volts , and the wire will be maybe 2' of 1/0, so a 100 amp breaker would work? I would have thought it would have something to do with the battery bank capacity, and max charge rate.

Does it have to pass inspection? I think the NEC calc works out to 125 Amps on this, but for my money 100 is close enough (as it is highly unlikely the panels are going to push the controller past its limit, so that just leaves the 'in case of short' problem from the batteries).

Always check the equipment manual first: you can't beat the info from the guys that make it. Usually. And in this case I trust MidNite over anyone else, including me.
Options
Re: Charge controller output circuit breaker rating question

Normal breakers and wiring are designed to carry 80 percent of rated current. Or take your maximum current times 1.25

86 amps x 1.25 = 107.5 amps.

Normally you would round up to next standard value. Or around 125 amps in this case.

you may get false trips if you under size the breaker/fuse.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 428 ✭✭
Options
Re: Charge controller output circuit breaker rating question
BB. wrote: »
Normal breakers and wiring are designed to carry 80 percent of rated current. Or take your maximum current times 1.25

86 amps x 1.25 = 107.5 amps.

Normally you would round up to next standard value. Or around 125 amps in this case.

you may get false trips if you under size the breaker/fuse.

-Bill

The Classic wire connectors will only go to 4 AWG, I have a 100 and an 80 amp breaker. Not sure witch would be better for the wire size. This breaker will be located in the
e panel between the CC and the positive battery terminal on the 125 amp breaker.
• Solar Expert Posts: 3,208 ✭✭✭✭
Options
Re: Charge controller output circuit breaker rating question

Am not a Code expert ...

But two things, "All MidNite circuit breakers can be used at 100% rated current when mounted in a MidNite enclosure"

The above quote from the product description on the MN Solar site, this covers the MNEPV 80 & 100A breakers as well as Panel Mount - MNEDC breakers.

The Classic Manual states that for a Classic 150 breakers between 80 and 100A and #4 AWG cable is OK. The exact recommended breaker value depends upon the Input voltage to the Classic.

Inside the e-panel, the short run of cable is really in free air (in many/most applications, depending on lead-dress), so in many such situations #4 AWG @ 75 degrees C can have a rating of 125A, and still be well protected by a 100 A breaker.

Opinions, Vic
Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
Options
Re: Charge controller output circuit breaker rating question

Just be really careful--I am not sure how the Midnite/Outback breakers are really rated... They have 60-63 amp breakers rated for use at 60 amp power levels. That is not how "code" rates breakers.

Code/UL/NRTL rated breakers and fuses are designed (usually) to operate at 80% of nameplate power--If you run at higher current levels, they may false trip.

So be very sure that you get what you expect.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 3,208 ✭✭✭✭
Options
Re: Charge controller output circuit breaker rating question

BB Bill,

Have used some Airpax DC breakers which are NOT rated for continuous duty at rated current, and have tripped those a couple of times right at rated current. These were run for many minutes at rated current and finally did trip -- this was on the output of a CC.

This question has come up on the MidNite Forum, and the answers that I have seen from MN, is that they are RATED for continuous current at the Amp rating for the breaker. This is all that I know.

There are specs from CBI published on the MidNite Solar site, but there are many curves, and have not been able to discover just which curve to use for these breakers.

As always, YMMV, "Follow the label, avoid excessive use" Good Luck, Vic
Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
Options
Re: Charge controller output circuit breaker rating question

Vic,

That is pretty much what I would expect for a "standard" rated breaker... Run for minutes to hours at rated current then trip (there are a lot of variables--And finding the trip curves for the breaker/fuses can be helpful).

I am not a big fan of (for example, no idea if this is what happened)--Getting an 80 amp breaker and marking it 60-63 amps for continuous rated current.

It sort of works in the DIY world--Where you tell somebody they have a 60 amp charge controller, so get the 60/63 amp breaker.

However, that raises confusion on the wire where NEC would require wire at 60 amps * 1.25 = 75 Amp minimum rated wire (if done to NEC code).

But, in a world where you do not have a lot of Licensed Electricians installing off grid systems--I guess the confusion is minimal if you stay in the "product family" (XYZ brand charge controller + Breaker + electric sub panel + properly rated at >60 VDC breakers and fuses vs automotive/truck/marine/aircraft rated stuff).

There is a lot of "slop" in the requirements even with UL... For example, can I use a 48 VDC rated breaker/fuse on a 48 VDC battery bank--Knowing full well that that you may see 60+ VDC when the battery is being charged (many old glass fuses are rated at 110-120 VAC on utility line power that goes upwards of 132 VAC and still be in spec.). I asked the UL inspector, and he just ignored my questions (I was designing a telecom system to run on a 48 volt battery bank... And the whole question of "touchable parts" on a 48 volt battery bank running at 60+ volts--And what ratings should a 60=72 VDC battery system use--Apparently in Europe, there were 60-72 volt telecom system).

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 428 ✭✭
Options
Re: Charge controller output circuit breaker rating question

I am still a noob so bare with me. Currently using the Classic sizing tool for the array that is planned I am looking at 58.3 amps (battery charging current). So with that in mind 58.3 * 1.25 = 72.9, so I would be better off using the 80 amp breaker (or buy a 75a) as the wire run is less than 6 total feet using 4 AWG at 48 volts.

Thanks Guys
• Solar Expert Posts: 5,183 ✭✭✭✭
Options
Re: Charge controller output circuit breaker rating question

Have you asked MidNite over on their site? Would be interested in their comments...

KID #51B  4s 140W to 24V 900Ah C&D AGM
CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM
Cotek ST1500W 24V Inverter,OmniCharge 3024,
2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
• Solar Expert Posts: 3,208 ✭✭✭✭
Options
Re: Charge controller output circuit breaker rating question

Dennis,

In the back of the Classic manual:
http://www.midnitesolar.com/pdfs/classicManual.pdf

... there is a table for selecting breakers. There are some factors that come into play. From your earlier posts, thought that this wire was essentially all within an e-panel, which would generally make it in free air, allowing greater Ampacity, BUT, at a six-foot length, perhaps some of this wire is in conduit (?).

Really, that wire table should be a good reference, and state MidNite's views on wire size vs battery voltage, considering input voltage and PV power.

Breakers protect wiring. At 75 degrees C, #4 AWG wire has an ampacity of 85 A in conduit with three or fewer current carrying conductors, and in free air is rated at 125 A.

I am NOT a code guru, and there are some intricacies regarding exactly how your system is laid-out, and therefore which code sections apply.

Seem to recall that that table recommended #4 AWG and an 80, or 100 A breaker. Vic
Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.