how much load ampere on 48v battery will be if the AC load is at max 5000w?

[mahdi89]

how much load ampere on 48v battery will be if the AC load is at max 5000w?

 

[newbostonconst]

Watts = Amps x Volts
5000 = ? x 48
5000/48 = 104.2

So 104.2 amps at 100% efficiency.

 

[eabyrd]

Watts = Amps x Volts
5000 = ? x 48
5000/48 = 104.2

So 104.2 amps at 100% efficiency.

But allow 10% for inverter overhead to be safe

 

[mahdi89]

Watts = Amps x Volts
5000 = ? x 48
5000/48 = 104.2

So 104.2 amps at 100% efficiency.

so JBD BMS 100A is not enough?

 

[Short_Shot]

But allow 10% for inverter overhead to be safe

15%

At full load they tend to drop in efficiency.

So.

5000/0.85 = 5882 and change.
At 48v that's 122 something amps.
At 52v that's 113 amps.

When mostly discharged with lithium cells approaching say 2.8v/cell (45v) it's over 130 amps, assuming the inverter is able to maintain stable output.

I'd plan for it to draw at least 150 amps to give some wiggle room, then start looking at surge current.

 

[Brett V]

You can piggyback two BMS if you have your heart set on the JBD but it would be cheaper to go another route.

 

[eabyrd]

15%

At full load they tend to drop in efficiency.

So.

5000/0.85 = 5882 and change.
At 48v that's 122 something amps.
At 52v that's 113 amps.

When mostly discharged with lithium cells approaching say 2.8v/cell (45v) it's over 130 amps, assuming the inverter is able to maintain stable output.

I'd plan for it to draw at least 150 amps to give some wiggle room, then start looking at surge current.

I sit corrected. Thanks. So 50% margin is proper then when scaling OCP and wiring on the DC side

 

[Short_Shot]

I sit corrected. Thanks. So 50% margin is proper then when scaling OCP and wiring on the DC side

50%?

Where did you get that from?

I mean I'm fine with 50% for OCP and wiring too but sometimes that's not viable when you start nearing 300 amps.

 

[eabyrd]

50%?

Where did you get that from?

I mean I'm fine with 50% for OCP and wiring too but sometimes that's not viable when you start nearing 300 amps.

Nominal 48 volt draw = 104.2 You recommend 150 (150 - 104) / 104 = .4423. I rounded 44% up to 50% for ease of math

 

[Short_Shot]

Nominal 48 volt draw = 104.2 You recommend 150 (150 - 104) / 104 = .4423. I rounded 44% up to 50% for ease of math

If you want to call that a 'rule of thumb' be my guest. It'll mostly be OK, most of the time.

However, so we're clear that I don't explicitly suggest that sort of thing:

'My rule of thumb is that a rule of thumb is usually wrong'.

In my opinion, if you're doing this sort of thing DIY you shouldn't touch it until you're totally comfortable with the (reasonably) proper math behind it rather than a quick and grossly oversimplified rule

Of course there's way more complex stuff behind all of it but simple ohms law this is good enough for field use.


Like I said though, it can lead to you oversizing things that you can't afford or simply can't do once you start hitting the limits of 4/0 cable. This can occur with people trying to run 5kw with 24 volts, and many do.

At that point that rule goes out the window and you need to either rethink the system design and components, or start actually looking at less cable length to increase the effective current rating. That last part is a big no-no under most local and national codes by the way.

 

[eabyrd]

If you want to call that a 'rule of thumb' be my guest. It'll mostly be OK, most of the time.

However, so we're clear that I don't explicitly suggest that sort of thing:

'My rule of thumb is that a rule of thumb is usually wrong'.

In my opinion, if you're doing this sort of thing DIY you shouldn't touch it until you're totally comfortable with the (reasonably) proper math behind it rather than a quick and grossly oversimplified rule

Of course there's way more complex stuff behind all of it but simple ohms law this is good enough for field use.


Like I said though, it can lead to you oversizing things that you can't afford or simply can't do once you start hitting the limits of 4/0 cable. This can occur with people trying to run 5kw with 24 volts, and many do.

At that point that rule goes out the window and you need to either rethink the system design and components, or start actually looking at less cable length to increase the effective current rating. That last part is a big no-no under most local and national codes by the way.

As the great statistician in the sky said. All models are wrong, but some are useful. The idea is to have a starting point to “gut check” the concept and then do your analytics based on real world usage observations,