SB50 Connector Power - Is it really limited to 50A continuous load?

[adunsulag]

Hey everyone, fellow newbie here. I looked through the forums and didn't see answer for this question, if it has been answered if you can point it out to me that'd be great!

I purchased the Growatt 48V system with the inverter sized at 3000W/6000W surge. I also have two of the big battery 48V NMC batteries. I watched @Will Prowse video and saw he had connected one of the batteries to the growatt inverter but I'm getting confused on my limitations with the SB50 connector.

My understanding is the SB50 is rated for 50 Amps of continuous current. However, the Growatt can draw 3000 watts of continuous power. If I'm calculating everything correctly, I believe this means the 48V growatt system comes out to 62.5 amps. Won't this create a fire hazard with the SB50 connector, if I'm running 3000W continuously?

The battery breaker is 63A (https://bigbattery.com/product/48v-li-ion-powerwall/), so the battery technically can support the 3000W, but I'm confused on whether the actual connector the battery comes with can support a 3000W continuous load. Shouldn't I just be limited to 2400 watts continuous load (50A * 48V)? I tried getting more information on the connector and I found this data sheet for the SB50 http://www.thunderstruck-ev.com/Manuals/SB50.pdf. It shows I can handle surges past 50A (even handling my 6KW Surge for the 5 seconds before the inverter breaker trips). Though, I think my battery's break at 63A will prevent me from surging that high.

This is a related question so I'm not sure if I should make a separate post, but I'm also confused on how the connectors work when connected in parallel. I'm assuming I can draw more amps from both batteries if they are connected in parallel to support my 6000W 5 second surge on the inverter. However, I'm thinking I would have to open the batteries up and change out the SB50 connector to something more beefy to handle the combined amps running through the circuit, right? Or is that just not possible?

Thank you for any help you can provide!

 

[tim0shel]

That rating for the SB50 from my understanding is consistent amps but can peak much higher for shorter burst etc.

 

[adunsulag]

@tim0shel so that means a SB50 connector is limited for consistent power at 600 Watts for a 12V system, 1200W for a 24V system, and 2400W for a 48V system right?

 

[Bob142]

My understanding is the SB50 is rated for 50 Amps of continuous current. However, the Growatt can draw 3000 watts of continuous power. If I'm calculating everything correctly, I believe this means the 48V growatt system comes out to 62.5 amps. Won't this create a fire hazard with the SB50 connector, if I'm running 3000W continuously?

According to the spec sheets I found, the Anderson SB50 connector is actually rated up to 120A (hot plugging to 50A). So that's not an issue. The limiting factor would be the size wire used. If it's 6 AWG (the max that will fit in the SB50 connector) it is fine.

You can find general information and the datasheets for the Anderson SB connectors on their resources page. Here's a snapshot from the datasheet I'm looking at for the SB50 connector.

 

[adunsulag]

@Bob142 Can you help me understand what the hot plugging means vs the low resistance? Under the hot plugging it says its great for batteries, which I guess is where I got confused.

My plan is to have a battery disconnect (circuit breaker, or some kind of switch+fuse), between the batteries and the inverter. So I shouldn't have to deal with hot plugging amp issue right?

Thank you for your help!

 

[Bob142]

@Bob142 Can you help me understand what the hot plugging means vs the low resistance? Under the hot plugging it says its great for batteries, which I guess is where I got confused.

My plan is to have a battery disconnect (circuit breaker, or some kind of switch+fuse), between the batteries and the inverter. So I shouldn't have to deal with hot plugging amp issue right?

Thank you for your help!

Hot plugging means you can literally put together or yank the connectors apart while under load. That's not your use case so don't worry about it. You will connect the batteries once and leave them connected.

The batteries you bought come with built-in circuit breakers. I don't think you would need to add more.

This is a related question so I'm not sure if I should make a separate post, but I'm also confused on how the connectors work when connected in parallel. I'm assuming I can draw more amps from both batteries if they are connected in parallel to support my 6000W 5 second surge on the inverter. However, I'm thinking I would have to open the batteries up and change out the SB50 connector to something more beefy to handle the combined amps running through the circuit, right? Or is that just not possible?

You wouldn't change out the connectors on the batteries. You can draw more amps when they are combined in parallel but that doesn't increase the amp draw on the individual batteries. The more batteries you have in parallel, the fewer amps each battery has to contribute to the total load.

To put them in parallel, you could either connect both battery cables to the Growatt battery terminals (I don't have one so I don't know if the terminals can accommodate two sets of lugs) or you could connect the battery cables to bus bars and then connect the bus bars to the Growatt battery terminals with one set of wires.

Edited to answer the additional OP question.

 

[mapguy525]

hot plugging is a physical connection/disconnection while power is flowing through connector

 

[Xerxes]

I have seen a youtuber video testing several types of connections where the SB50 connection melted at 190 Amps.
There are several variables besides the connectior, like the crimp, the wire.....

 

[apctjb]

If it's 6 AWG (the max that will fit in the SB50 connector) it is fine.

Per the Growatt 3000 manual the minimum cable size required is #4; so if the SB50 is limited to #6 that sounds like a problem...

 

[adunsulag]

@Bob142 Thank you for answering my additional question. That was very helpful! The growatt only has one set of lugs for battery input so I'll need to connect via the bus bars route. When batteries are connected that way via bus bars, I think that means I need a separate BMS system to monitor the charge across both batteries. Do you know if that's correct? There's probably more information on the forum so I'll dig into that.

 

[adunsulag]

@apctjb I do see on page five it shows a recommended wire size of 1*4AWG, it also shows a 2*8AWG which I'm not sure what the 2* means. I'm not sure why the manual is recommending a 4AWG wire. Do you have any insight into this?

I saw @Will Prowse do the wiring with 6AWG for the short run he did on the 48V big battery video demonstration here:

Looking at some wire calculators it looks like if my one way length is 1.5ft 6AWG will handle 125A (max 6000W inverter surge) so I'm not sure why growatt is recommending 4AWG unless the run length is going to be longer from the battery to the inverter?

https://www.calculator.net/voltage-...e=1.5&distanceunit=feet&amperes=125&x=54&y=32

I appreciate all of your help.

 

[Bob142]

@Bob142 Thank you for answering my additional question. That was very helpful! The growatt only has one set of lugs for battery input so I'll need to connect via the bus bars route. When batteries are connected that way via bus bars, I think that means I need a separate BMS system to monitor the charge across both batteries. Do you know if that's correct? There's probably more information on the forum so I'll dig into that.

The batteries you bought each have a built-in BMS so I'm not sure what you're getting at.

Check out Will's video below for an example of hooking up multiple battery banks to all-in-one systems using bus bars. Right about a minute in he starts talking about the different battery banks and you can see that they are all connected to the same positive and negative bus bars mounted beneath the two all-in-one systems.

It doesn't matter that he has two all-in-one units and you have one. The point is that multiple parallel battery banks, each with their own BMS, are wired into positive and negative bus bars. The all-in-one units battery connections are also connected to the bus bars.

 

[adunsulag]

@Bob142 Thank you for the video reference. For some reason I thought that my all-in-one growatt system would somehow unevenly charge the batteries if they weren't directly connected to the inverter.

I had watched another video of Will's somewhere where he builds some batteries and it talked about cells diverging over time and somehow I was thinking that the two batteries would drift over time in their charge/discharge cycles and the inverter wouldn't know how to handle that. My apologies if I'm being confusing, I'm trying to wrap my head around it all as I'm learning a lot about all of this.

From the video as you discussed it looks like I should be able to easily wire everything together via the bus bars, so this has been very helpful and I appreciate that. Thanks again.

 

[Deleted member 1888]

Do the length of the wires matter at all? This post make it look like you will have problems if the wires are different length.

SmartGauge Electronics - Interconnecting multiple batteries to form one larger bank

 

[Ampster]

I think that means I need a separate BMS system to monitor the charge across both batteries.

No, you don't need anything to manage the charge across the batteries. Because the batteries are in parallel the voltage will always be the same. If the capacities of the batteries are different there will be eddy currents as they charge and discharge but the nominal wire size should suffice. That is one reason to have a separate circuit breaker or fuse on each battery.