# circuit breaker tripped by Suresine inverter?

Solar Expert Posts: 192 ✭✭
Weird thing happened this week at the cabin. I have a 300 watt Morningstar inverter. It is hooked through the DC breaker panel to a 20 amp breaker. I got up one morning and turned on a fan and the power went out? I'm mostly AC so I checked the AC breakers and they were fine. They are 15 amps each. So I checked the main breaker panel that the dc/battery and charge controller work through and noticed the 20 amp Suresine breaker tripped. The sun had just started hitting the panels and so the volt meter on my CC showed 12.5 volts.

Here's my quandary. I believe the batteries were at a true level lower than 12.5 volts and that the issue has to be with the Suresine low voltage disconnect. If this is the case, then when I turned the fan on, it drew the real battery voltage level (the one the inverter sensed) below the LVD level and the power was disconnected from the Suresine. What I don't understand is why it would trip the 20 amp breaker the inverter is hooked to on the DC side? SHouldn't the LVD simply stop power going to the AC breakers? I realize I could put a larger breaker on the DC side, but still why would the LVD trip a breaker on the DC side? Sorry for the long post.

Tim

PS-this is a perfect example of how CC meters are NOT necessarily real battery monitors. I really have to get a real one!

• Solar Expert Posts: 5,433 ✭✭✭✭
Re: circuit breaker tripped by Suresine inverter?

How low was the battery? 20 amps at 12.5 vdc is 250 watts

That same 250 watts from say 10 vdc would be 25 amPs.

Tony
• Banned Posts: 17,615 ✭✭
Re: circuit breaker tripped by Suresine inverter?

And how big is the wire connecting the inverter to the battery? Small enough wire + high enough current = Voltage at the inverter significantly less than at the battery, especially on a 12 Volt system.
• Solar Expert Posts: 318 ✭✭✭✭✭✭
Re: circuit breaker tripped by Suresine inverter?
icarus wrote: »
How low was the battery? 20 amps at 12.5 vdc is 250 watts

That same 250 watts from say 10 vdc would be 25 amPs.

Tony

Ding Ding, we have a winner!
• Solar Expert Posts: 10,300 ✭✭✭✭
Re: circuit breaker tripped by Suresine inverter?

odd as 20a x 12v = 240w and for 300w it should be a 25a cb or fuse on the dc side. be very sure of the fan draw too as it could spike above 300w on startup and pop the fuse or breaker.
• Solar Expert Posts: 3,009 ✭✭✭✭
Re: circuit breaker tripped by Suresine inverter?

I run both of my Suresine 300's using a 30 Amp, Slo-Blo fuse on the DC side, one for each inverter. In all overload incidents I have encountered, the inverter shuts down before the fuse blows. 20 amp is probably a bit light for a fuse. The inverter will put out 300 watts continuous, and up to 600 watts surge,, which could result in a 12 volt supply surge of about 50 amps. Also, be aware that some fuses are designed to be sensitive to heat buildup at it's terminal connections. reason being, if the fuse gets loose in the holder, or has a corrosion buildup, it can build up heat that could otherwise case a fire. Check the blown fuse for any signs of arcing or burning. If it exists on the fuse, it will also exist on the fuse holder,, and if not cleaned up, will damage the new fuse.
• Solar Expert Posts: 192 ✭✭
Re: circuit breaker tripped by Suresine inverter?
icarus wrote: »
How low was the battery? 20 amps at 12.5 vdc is 250 watts

That same 250 watts from say 10 vdc would be 25 amPs.

Tony

That's part of my problem...I have no idea how low it actually was, as the volt/amp meter on the CC stated 12.5. But, that was after several amps from the panels had already been putting energy into the batteries. I really need a good battery monitor. If nothing else, this has revealed that.

The wire size is 6 gauge which might seem light, but 1) I've never had this problem before, and 2) I'm not sure my CB would take a larger diameter wire.

I'm thinking I need to do 2 things: 1) Buy a battery monitor and 2) replace the 20 amp CB with a larger, say 30 amp, CB.

Does that sound logical?

Tim

BTW - Does the CB on the DC side have any effect on the 40 amp fuses inside the unit? IN other words if I put a 50 amp fuse on the DC side would that override the 40 amp fuses inside and possibly "kill" the inverter? Just wondering how all this goes together.
• Banned Posts: 17,615 ✭✭
Re: circuit breaker tripped by Suresine inverter?

6 AWG wire should be plenty for the MS 300.
If you look at the maximum output vs. the minimum Voltage you get 30 Amps of current. 6 AWG will handle that easily.

If you put a 20, 30, or 50 Amp breaker in line with the built-in fuses the one that will blow/trip first will be the smallest one. In other words your 20 Amp breaker will trip before the 40 Amp fuse blows. If you put a 50 Amp breaker in, the 40 Amp fuse will blow before the breaker trips.

Somehow you got into a situation where the current exceeded the 20 Amp breaker's capacity long enough to trip it. That's at least 200 Watts and up to 240. Notice that MS puts 40 Amp fuses in. Manufacturers usually know what they're doing.

Bigger breaker? Yes. Battery monitor? They're nice, especially on sealed batteries.
• Solar Expert Posts: 192 ✭✭
Re: circuit breaker tripped by Suresine inverter?

Well that's good to know on the wire front. I thought I had figured that out when I installed 2 years back. I will put a larger CB in and get a battery monitor. This situation is a good learning experience for me since the smallish CB blew and this action has caused me to see a problem with my system or how I have used it. If it hadn't blown I might not have realized 1) that my circuit breaker is a bit small, 2) that I need a battery monitor and 3) that my batteries were so severely discharged. I look at it as a wake up call on my trainer batteries. That's what all you call them and now I know why. Better to learn this on a set of golf cart batteries than a set of crowns.

Thanks for all the help. I learn more every day, as someone here has said.
• Solar Expert Posts: 10,300 ✭✭✭✭
Re: circuit breaker tripped by Suresine inverter?

go with a 30a cb as was already suggested and that should work well for you.