Unknown wattage of machine advice

[flameport]

So I can then purchase the correct cable size for inverter.

Why is an inverter required for something that already uses 13V DC?

 

[BS3036]

Is the plan to run this mobile? If so it would be better to ask the actual question instead.

 

[ipbr21054]

So many different replies.
I am to fit an inverter in the jeep.
I need to order the correct size cable for when i connect it to the 12v battery & the run the cable to the inverter.
I need to know the wattage of the motor so try & find out the cable size i need to order.
I advised if the charger would help you say what size the motor might be by the label.
Yes for mobile purposes.


12v Battery in jeep.
Inverter is 500w / 1200w
From battery to inverter is 3 meters or under.

When machine is running on 12v you hear it running at say a certain decible.
When the charger is connected to machine / mains & you switch it on you can hear the decible increase.

Also the finished cut key when using the mains is a far better smooth / looking cut.

So i am in need of ordering some cable but without the amperage / wattage of the motor i was stuck

 

[ipbr21054]

You can't get mains rated cables under the size required for 120 watt, it is around ½ an amp. O.5 mm² is ample, on the 13 volt size the charger shows the current 0.8 amp so likely 1 mm². Your not really worried about what the motor uses, only what the charger takes or delivers.

I know that so thats why i wrote "So I can then purchase the correct cable size for inverter"

 

[ericmark]

A battery to battery charger will have it's own current limiting device, not sure why you need one when already 13 volt? The battery charger you have is an inverter, the word means in electrical terms to transform voltage or current with some form of regulation normally by turning the 50 Hz into DC then turning it back into AC not always at the same frequency.

One type is a using DC from a battery turning it to AC and also transforms it up, to 230 volt, however powering one inverter from another can cause problems, as this turning AC to DC often involves a capacitor and inrush to charge that capacitor, I tried to charge my mothers mobility scooter by using a step up and step down inverter in the car, step up was 150 watt output, and step down 120 watt, theory should have worked, in practice it worked when tested at home with a fully charged scooter, but when I tried to recharge the scooter it failed. I had to use double the output and a 300 watt inverter.

It is not helped as many small step up inverters use a simulated sine wave, which can upset some step down inverters. Also cable sizes tend to get rather large, so 16 amp is normal max for a cig socket hence loads of 150 watt step up inverters, but over 150 watt looking at larger fuse and cable, my 300 watt is built into my jump start pack, that is how I charged scooter, jump start pack charged from cig socket, and scooter charged from jump start pack, not at the same time.

So 8 amp is a fair current, you would not want to be using that from the main vehicle battery for long without engine running, I would not think you really need 8 amp, the Sterling DC to DC charger at 3 amp is likely enough

This unit isolates two batteries but allows one to be charged from the other, it is designed for lead acid what we don't know is what battery is fitted in the key cutter, but if a VRLA then likely this is the sort of thing you need.

However I would personally simply use a fused lead from cig lighter socket and see how it works, the problem is if you forget to unplug when you start car it may blow fuse, but the inverter shown is around £66 so seems a lot of money when key cutter is 13 volt and vehicle 12 - 14 volt.

 

[Harry Bloomfield]

12v Battery in jeep.
Inverter is 500w / 1200w
From battery to inverter is 3 meters or under.

If the battery built into the machine is a 12v one, why are you bothering with an inverter at all? Jeep 12v > inverter 240v > PSU 13v > machine.

Why not simply power the machine directly from your Jeeps battery, it will also be much more efficient.

At such low voltages you not only need to have the correct current rating, but a sufficiently large cable to avoid too much volts drop in the supply cable.

 

[ipbr21054]

If i run the machine direct from the jeep YES it works BUT in my previous post i mentioned i get a much bettery clean / smooth cut when mains connected.

So at home i have the mains connected to the machine all the time to get much better looking keys.

So my plan is to put the machine in the jeep now & then for mobile use and to run it at mains level.

So my battery will supply the inverter then i will connect the charger to the output side of the inverter now 240v into & running the machine.

Ive tried before just at running it from the jeep at 12v but wasnt very good.
What happens when it gets flat etc,connected cig wire & after a few moments just blew the fuse.

So im going the 240v way

 

[Harry Bloomfield]

Ive tried before just at running it from the jeep at 12v but wasnt very good.

Maybe related to volts drop, especially if plugged into a ciggy socket, powered via thin Jeep wiring, with poor connections?

What happens when it gets flat etc,connected cig wire & after a few moments just blew the fuse.

No great surprise, a motor can take a large current on initial starting.

Try this- Make your connections directly from the battery, but add a 30amp fuse into the +ve lead. Try it with no more than 2m of 2.5mm, from battery to the machine. To repeat - with such a low supply voltage, the current is not so much a concern for the cable size, as the volts drop under load between source and load.

 

[ipbr21054]

The above then advises to run it using 12v but i need to go with an inverter.


How can the voltage drop be calculated if we know the following.
Cable run 3 meters or less
4 AWG wire
Diameter of 4AWG is 5.1894 "21.1506 Area mm2"
Supply 12v battery
Inverter 240v
Machine motor 300w or less.

Then if lower than 3% all should be ok ?

 

[ericmark]

What happens when it gets flat etc,connected cig wire & after a few moments just blew the fuse.

There are blocking diodes, split charging relays, and inverters all used to charge or use car supply mainly in caravans often with some device to switch off once battery voltage reaches a critical level.

Years ago I used a Lucas unit designed with the idea the second battery is charged when the vehicle is being driven, and used when stopped so independent of the vehicle start battery, today I use a jump start battery. One will likely cost around £50 and has mains charger, and between a 10 Ah to 15 Ah battery, with a cig lighter lead which can also be used for charging. Typical car has 35 Ah to 95 Ah battery, and it needs half that to start, so if 15 Ah is not enough then using the car battery is also going to cause problems.

A 32 Ah car battery will cost around £36, so yes cheaper option, but a car battery is not designed for deep cycling the VRLA or AGM battery in a jump start unit is OK with deep cycling, if you can has stop/start technology then likely fitted with an AGM battery, but otherwise likely a flooded battery, which will not like being discharged even to half charged state.

So with AGM battery we start at 10 Ah at £18 and as we go up they get more expensive 20 Ah at £30 and 34 Ah at £44 over that getting a bit heavy to carry, a split charging relay costs around £9.

For £145 all built in 35 Ah battery and 300 watt inverter and no risk of discharged car battery. Weight 14.258 kg, you would not want any bigger due to weight. My mobility scooter batteries are 35 Ah and would not want to carry them far.

 

[ipbr21054]

The last post i believe is on a different path to what i am on.
I dont want to carry anything.
The Jeep battery is 57amp

Reading back over all these replies has no0w got me confused as some are just replies which maybe have no affect on my original post

 

[Harry Bloomfield]

I think the point Eric is trying to make, is that you might be better - as in not discharging your Jeeps battery and being unable to start it, if you were to use a deep discharge battery, otherwise known as a leisure battery. They are designed to accept regular discharging and survive the treatment, a vehicle starter battery is designed for a rapid heavy discharge, followed by an immediate recharge.

You would connect the second battery to the first one, via a voltage controlled relay - commonly sold by caravan accessory dealers and some car part shops. As the voltage rises across the main battery, when the vehicle is started, the relay makes to charge the second battery. When the engine is stopped, voltage falls and the relay disconnects, so only the second battery supplies your machine whilst parked.

Acceptable volts drop depends on the initial voltage across the battery and what is acceptable to your machine. You can easily measure it, by checking the voltage at source and at the machine under normal load. Your calculated drop of 3%, would produce a drop of 0.36v. 12v will be 11.64v at the machine.

For comparison - I used to plug my charger into the ciggy socket, until I realised how much volts drop there was between plug and the battery. From memory - charger was showing 14.2v under load at the plug, battery voltage was only 13.7v, too low to provide an effective charge. 0.5v dropped through three fuses and cars loom wiring.

I added an extra lighter socket, just for charging and wired directly to the battery via a 20amp fuse, resulting in no measurable volts drop and proper charging.

Many tow-bar fitters (and some manufacturers too) install a 15amp cable to power 120w fridge a caravan battery charging, the length of the tow car, A frame and part way down the caravan, a run of possibly 25 feet. Due to load and volts drop, you are lucky to get 9 or 10v at the fridge, with 20amp cable. I run 2x 4mm in parallel the length of the car, to overcome the drop.