Stumped on an inverter

Question

I'm disabled and am looking to be able to charge my power chair whilst I'm on the go in my vehicle, the problem is that I know what my charger draws and outputs in Volts and Amps, but all inverters' power outputs are in Watts, totally confusing!

The charger is a 110/240V in the wall charger and the output is 24V @ 5Amps. So the question is what size inverter do I need in order to be able to use this charger in my vehicle?

Any help will be gratefully received as my hair is now suffering from so much head scratching..

Answer 1

I assume that your "in the wall charger" is not a charger per se, but a 24VDC power supply, and that the actual battery charging circuitry is integrated in your chair or in the battery pack in your chair.

The rest of this answer is based on the assumptions in the above paragraph. If any of them are not correct, you should disregard the answer.

However, if the assumptions are correct, the solution is potentially relatively simple.

If the chair charges from 24VDC, and your car has 12VDC, you can skip the AC (inverter) and the wall power supply (the "charger") altogether.

Use a suitable 12VDC to 24VDC boost converter.

It will be lighter, cheaper and probably more efficient than using an inverter to convert 12VDC to 110/240VAC and then to 24VDC.

Some requirements:

• The boost converter must be able to supply a stable 24VDC at 5A to the charger integrated in your chair.
• Naturally, you'll need to equip it with the correct plug.
• The boost converter must be able to tolerate up to at least 15VDC on the input, and possible spikes of even higher voltage, because the voltage in a car can vary quite a lot.
• The car must be able to supply at least 10A at 12V without blowing a fuse or catching fire.

You should speak to an electronics and/or car professional about this. While it's not rocket surgery, there is quite a bit of energy involved. Also a potential (lithium battery?) fire hazard in a moving vehicle. All in all, you should make sure that it's done right, or not at all. Hopefully this answer can point you in the right direction.

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Edit: If the wall charger is an actual multi-stage battery charger, like the one in your link, the answer above doesn't apply. But did you ask the supplyer of your charger if they also have a model that can run on 12VDC?

The website was pretty sparse on technical details, but the batteries on the site seem to be lead-acid type batteries. There are plenty of chargers out there for 2x12V lead acid batteries, that can take a 12VDC input.

I tried to google "24v battery charger 12v input", and found several retailers. If your usual retailer doesn't sell 12VDC driven 24V chargers for your particular type of battery, I'm sure somebodye else does.

If you find a suitable and compatible charger, I personally feel that would be a "cleaner" solution than using an inverter. That being said, using an inverter together with your existing charger would likely work too.

Answer 2

Just FYI, this isn't exactly the type of question this SE typically answers, because it is a shopping question. That being said:

There are two things here:

1. Your chair's power needs
2. Your car's ability to deliver that power

Point 1: Inverters are defined in watts because that is enough to describe the output capability of the inverter. Watts are defined to be Volts\$\times\$Amps. If in the US, all inverters will provide 120Volts (unless otherwise specified), so a 120W inverter will provide 1Amp @ 120V. If your chairs charger charges the chair with up to 5A @ 24V, then you need an inverter that can do at least 120W. This is not the inverter you should buy though. The reason is that inverters and chargers are not perfectly efficient in conversion. To be on the safe side, it's best to assume about 80% efficiency for each converter. There are two converters in line, so assume that 80% efficiency twice, this means your minimum safe wattage should be about 190W. Which brings us to point 2.

Point 2: your car's accessory power socket (cigarette lighter socket) is usually fused with a 10Amp fuse and (again, if in the US), your car's electrical system will be 12V. This means most vehicle accessory power sockets are only capable of delivering 120W before the safety components disconnect the socket. This means you will need an inverter which can wire to the battery terminals.

As far as a specific recommendation, I can't give one.

But, in short, what you are looking for is a: 200W inverter with a direct-battery connection with a 20A fuse.

Hope this helps.

Answer 3

If the battery charge management logic is inside the wheelchair and not inside the "charger" (this means the "charger" is in fact just a power supply) this solution would be simplest and most efficient.

If the wheelchair has lithium batteries, this is likely to be the case. Even for lead, as you'd need a little bit more than 24V to charge a 24V lead battery...

here

here

Otherwise (charge management logic inside the charger) then this will not work...

Answer 4

Watts = Volts * Amps

Output is 24V @ 5 Amps. That's 24*5=120 Watts. Give your inverter some extra breathing space and you'd need say 150 Watt inverter (or higher).