What is the max. continous discharge current?

[Timm0]

The person I contacted to build a 12 2500wh lithium-ion battery pack asked for this:

"how about the Max. Discharge Current? And continuous discharge current? it's required for protection circuit(BMS)"

But I don't know what this terms are?
Pls how can I know how to calculate them?

 

[Jon_K]

They are asking you how what the max amps will be (peak and continuous) for whatever it is you are designing/buying.

 

[Timm0]

They are asking you how what the max amps will be (peak and continuous) for whatever it is you are designing/buying.

Do you mean the max amps the appliances will be drawing when in use?

 

[Hedges]

Do you mean the max amps the appliances will be drawing when in use?

Something like that, but not exactly.

If your battery pack is 12V, he is asking how many amps will be drawn from the battery pack.
Your appliances, if they are not 12V appliances in an RV, probably use 120VAC from an inverter.
The current (amps) drawn by a 120V appliance isn't one-for-one with current drawn from battery.

If you have a 1200W appliance at 120V, the current it draws is 1200W/120V = 10A AC
But for an inverter to provide that much power, it has to draw the same amount of power from the battery.
Battery is lower voltage, so higher current.
12000W/12V = 100A
So about 100A continuous current would be drawn from the battery, if inverter was 100% efficient.
assume inverter is 80% efficient.
100A/0.80 = 125A, so that is the continuous current.

Do you have any loads with a motor? Starting a motor requires additional current. You may notice that lights dim momentarily when it turns on.
Whatever the label rating is, multiply it by 5 as an estimate.
I have a window air conditioner rated 480W, 4A at 120VAC. It draws about 2400W for an instant, 20A
2400W/12V = 200A instantaneous. For inefficiency, 200A/0.8 = 250A max discharge current
480W/12V = 40A. 40/0.8 = 50A continuous discharge.

 

[chrisski]

I don't know what the max discharge current is, but I recently contacted tech support for my 232 ah at the 20 hour rate 6v golf cart batteries and asked what the max discharge current was, and they told me the max discharge was 350 amps. Honestly not sure what that 350 amps means, but I doubt my 4/0 wiring would hold up very long to that, and hopefully my 200 amp fuse would blow fairly quick. If I were to discharge at the 350 amp rate because of the Puekert effect, I would expect those batteries to last for minutes before dying.

Since I asked tech support to see how many of these golf cart batteries I needed to run a microwave, I probably wanted to know the Max Continuous Discharge and how long they could sustain it.

 

[MisterSandals]

lithium-ion battery pack

Is that Li-ion (as stated) or LiFePO4 ... the answer depends upon this somewhat.

 

[Hedges]

Your 4/0 wire should be fine at 350A as long as the golf cart battery can supply it (maybe 15 minutes)
If 90 degree insulation and ambient is 30C, 4/0 single conductor in free air is good for 405A
But voltage drop may be excessive, depending on length.

200A x 12V = 2400W, more than enough for a microwave (probably up to 1800W AC)

The 350A (4200W at 12V) is good for starting surge of a motor rated 800W.

 

[chrisski]

The 350A (4200W at 12V) is good for starting surge of a motor rated 800W.

I think that is what intent of the 350 amps. For me, I'm trying to figure out how many more golf cart batteries I need to run the microwave for 15 to 20 minutes at night. I think the term I need to ask the battery manufacturer is max continuous discharge. Tentatively, I'm thinking two more batteries plus panels to supply that.

 

[Hedges]

A 1000W microwave drawing 1800W AC for 20 minutes is 600 Wh.

A pair of 6V, 223Ah golf cart batteries is 2676 Wh. Drained to 50% DoD, 1338 Wh avalable. Your microwave only uses 1/2 of that, 25% DoD.
So just two batteries total is enough. That could give you 2 days autonomy without sun, 3 days if you go to 75% DoD when that happens.

Sunshine provides 2 hours to 6 hours effective full sun hours. 600W/2 = 300W of panel would be enough if everything 100% efficient and panel delivered STC rating (which it won't.) About 400W of panels might be good, assuming they are tilted toward the sun. This is probably on a vehicle, so I suggest a tilt mount if you'll be using it in the winter.

 

[chrisski]

@Hedges thanks. I’m dealing with what I consider an unneeded real world math problem for max amps.

Found out that when I went to sleep the other three in my RV were using the microwave, not the 20 minutes I mentioned, but math in my head tells me three minutes of microwave usage translated to one hour of our normal usage.

Apparently I’m the only one capable of pulling the cord on the generator and switching the plug.

 

[Timm0]

Li-ion

Is that Li-ion (as stated) or LiFePO4 ... the answer depends upon this somewhat.

 

[MisterSandals]

Li-ion

You should do a search on "explody" on this forum before proceeding in that direction.

 

[Timm0]

Something like that, but not exactly.

If your battery pack is 12V, he is asking how many amps will be drawn from the battery pack.
Your appliances, if they are not 12V appliances in an RV, probably use 120VAC from an inverter.
The current (amps) drawn by a 120V appliance isn't one-for-one with current drawn from battery.

If you have a 1200W appliance at 120V, the current it draws is 1200W/120V = 10A AC
But for an inverter to provide that much power, it has to draw the same amount of power from the battery.
Battery is lower voltage, so higher current.
12000W/12V = 100A
So about 100A continuous current would be drawn from the battery, if inverter was 100% efficient.
assume inverter is 80% efficient.
100A/0.80 = 125A, so that is the continuous current.

Do you have any loads with a motor? Starting a motor requires additional current. You may notice that lights dim momentarily when it turns on.
Whatever the label rating is, multiply it by 5 as an estimate.
I have a window air conditioner rated 480W, 4A at 120VAC. It draws about 2400W for an instant, 20A
2400W/12V = 200A instantaneous. For inefficiency, 200A/0.8 = 250A max discharge current
480W/12V = 40A. 40/0.8 = 50A continuous discharge.

Thank you