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# Usbs on 24v

## Usbs on 24v

(OP)
Hello everyone,
I currently have a bus that works on 24 volts, I'm looking to install USB ports by each passenger seat. There are 9 seats and each USB component, had two ports ( 5v 1 amp and 5v 2.1amp).these components can seemly run on either 12v or 24v.
My question is if the batteries/electrical system would be able to handle the load say if all 18 ports are being used at the same time along with other accessories such as radio & amp, roof lights etc
Thanks!

### RE: Usbs on 24v

Most chips that support USB power generation use PWM switch-mode power conversion. The fact that the USB ports work with 12V or 24V seems to be firm evidence that your ports use this type of chip. Assuming 80% efficiency (they're usually better than that), a 5V 1A port is 5 Watts/0.8 or requires 6 watts input power. A 5V 2.1A port is 10.5W/.8 or 13.125W

The ports when not in use are going to pull very little current. So, we will calculate the worst case. Every seat is filled and every USB port is being used to its maximum capacity (very unlikely). 9 seats x (6+13.125) or 172.125 Watts.

At 24 Volts, to produce 172.125 watts requires 172.125/24 or 7.17 amps. Actually a 24 volt system is higher voltage, so the current would be most likely lower.

7 amps of additional load on a 24 volt system is really insignificant. And this is the worst case of the worst case. You're OK

### RE: Usbs on 24v

You need to look at the reserve capacity of the battery. A typical Econoline battery has a 100-minute reserve capacity, which is at 25A. Assuming you have 7A, not counting any other loads, you would have a reserve capacity of 350 minutes, which is not even 6 hr. When you add in other loads, the time decreases further. There are bigger batteries, but they'd have to fit somewhere on the van.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
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### RE: Usbs on 24v

What IR is saying is that 7A will add up on the battery when it's not being charged. Say the van is off and people are still using power. If this is a commuter type operation no one will be sitting around in the van when it's not running.

Keith Cress
kcress - http://www.flaminsystems.com

### RE: Usbs on 24v

That's only a problem if you leave the ignition on but the engine is not running. That assumes you are using an accessory circuit, ie through the key, not hardwired to the battery of course.

Cheers

Greg Locock

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