Converting charger for Karcher Window Vac. YAPP

Trundlebug

Trundlebug

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Last year I bought a second hand / refurbished Karcher window vac from a market.

It only came with a mains charger but I have the intention of converting it to charge from a 12v cigar socket.

The mains charger states the output as 5.5v and 600mA

I've noticed that my 12v USB charger output is 5v and 1000mA, and I'm wondering if this is close enough to do the job without causing damage.

What do you think?
Will 1000mA be too much current and cause damage? Or will it just decrease the charging time?
I'm figuring the half a volt reduction won't make much difference, am I wrong? I appreciate I may not get quite a full charge into it as a result, but I can live with that as long as I can recharge at will when away form shore power.

As yet I haven't seen a cross section of the wires from a USB, are there more than two? In which case, which ones should I use for this application?
 
Typically your vac will have 4x NiMh batteries. (or Nicad). These have peculiar voltage characteristic in that they present 1.2 volts from almost flat to fully charged.
Now battery charging requires that you present a voltage that is in excess of the inherent voltage of the battery. Only the excess will push current in.
So my guess is that 5v (closely regulated) will not get much charge into 4x NiMh batteries. 5.5v will.
My suggestion is that you charge from 12v via a resistor or a 6v regulator like 7806. A resistor of 12 ohms will drop the voltage and give aprox .5 amp from a 12v battery.
This will rise to about .7 amp on a 12v battery on charge (14v). Much depends on the size of the batteries in the vac. They may only be 2 amp hour or so in which case 4 hrs charging will charge them and any more may destroy the batteries. So far safer if you don't mind waiting is a 100 ohm resistor for about 20 hrs charge. The resistors need t be high wattage (5w) as they will get hot.

On the other hand if you can run the vacuum on the USB socket you should run it quite well but won't get much charge in. Sorry can't describe the 5v lines for USB socket.
http://en.wikipedia.org/wiki/USB might help. It looks like the outer pins are for power +ve and -ve. good luck olewill
 
Why not install an inverter and use the original charger? The inverter might prove useful also for other appliances.
 
aluijten said:
As nobody asks, I will. What is the use of such a thing on a boat. Is it you have a Mobo with large windows/portholes?
Click to expand...

Don't Mobo's come with big patio doors where such a beast would be helpful?

Just done all of our windows outside at home in an hour (bungalow) so hardly a slow motion device!
 
Thanks for the replies so far.

To address the points raised:

1. I already have the "proper" charger. Unfortunately it's mains only and doesn't work on 12v, hence the project. There isn't, as far as I'm aware, a 12v charger sold for it.
2. Buying an inverter is an expensive solution and will more than likely cost way more than the £35 I paid for the Karcher in the first place. I appreciate it could be done that way, but then so can anything if you throw enough money at it. That isn't in the ethos of "P"BO.
3. Yes I do have a Mobo and it does have patio windows at the rear of the wheelhouse, but they aren't the main areas of concern. All the other windows (windscreen, wheelhouse sides and saloon windows mainly) especially above the sleeping area get a lot of condensation on the inside in the mornings at this time of year and in autumn when the evenings are cool. I used to use a microfibre cloth to wipe down in the mornings but this gadget was on offer and at the price I thought it was worth a try.

It works very well and is a lot quicker than a cloth, but it doesn't last long on a charge (seems to self discharge quite a bit) which could be explained by it having NiMH batteries, of which I'm not much of a fan. That wouldn't be a problem if I could recharge it easily.

I can see a bit more research may be required.
Thanks for the info so far anyway. Anyone else have any suggestions?
 
AFAIK, Karcher window vacs (may be a knock-off copy???) are only made with lithium batteries; ours is used most mornings to suck up the condensation from bathroom and bedroom widows (old, cold house) and the battery lasts couple of weeks between charges. If yours is not holding charge, it could be the batteries are a bit duff. Lithium batteries can become a bit fiery if mischarged/misused and the charger or battery have a regulator built in to avoid this. Google 'overcharging lithium battery video' for several examples of incidents you may prefer to avoid on your boat. I'd be wary of leaving it charging it anywhere unattended if I wasn't sure about about the condition of the batteries.

J
 
Having just looked at the mains charger for my Karcher window vac I see that the input is 240v @ 0.2A which is around 48 watts. Screwfix do a Ring Mini Inverter which plugs into a cigarette light socket and gives 75 watts for £23.33 or a slightly larger Power Source Inverter giving a maximum power output of 150 watts for £20.83. I would have thought that either of these units would serve the need.
 
Trundlebug said:
Thanks for the replies so far.

To address the points raised:

It works very well and is a lot quicker than a cloth, but it doesn't last long on a charge (seems to self discharge quite a bit) which could be explained by it having NiMH batteries, of which I'm not much of a fan. That wouldn't be a problem if I could recharge it easily.

I can see a bit more research may be required.
Thanks for the info so far anyway. Anyone else have any suggestions?
Click to expand...

Why don't you remove the batteries altogether, put a voltage convertor in and run the thing from a 12 Volt outlet. That saves a lot of trouble and you can use it for extended periods. I presume you don't own a boat so big the supply chord becomes a problem.
 
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