Invertors?

[79commando]

Just to put the cat amongst the pigeons surely as the drill is say 800W the invertor has an output of 240v so the drill draws only 3.3 Amps. Dont ask me about the science between turning 12v into 240v; all I know is that a 65 Amp alternator handles my 1500W invertor no probs although it would be a good idea to get two spares batteries wired in parallel and fed by a trickle charge. This would power an invertor attached to the batteries by jump cables for most purposes.

[Varjeal]

Definitely run at LEAST a 1500 to 2000W inverter if you plan on running drills, etc from it. Another option is to run a deep-cycle or marine battery with a trickle charger from your main battery feeding it. Make sure to use overload protection, and it probably wouldn't hurt to have a switch in their somewhere too.

Generators aren't always practical as some lockies (including myself) use smaller vehicles where a generator simply isn't an option.

[79commando]

More problems with using a generator is where to store the fuel and if running the generator it must have an exhaust leading to the outside of the vehicle. Up here in the colonies in some areas if you had your generator running outside the van and a long extension lead to power the drill etc at the customers door the length of the extension cable will be directly proportional to how much of a start the generator thief gets. I swear by my invertor; stored inside the vehicle with the extension lead running via the door seal. I can lock my van and with the use of the extension lead work away happily.

One in three people have a mental health problem. If you check out two of your mates and they are ok chances are it's you.

[MrB]

Just to put the cat amongst the pigeons surely as the drill is say 800W the invertor has an output of 240v so the drill draws only 3.3 Amps. Dont ask me about the science between turning 12v into 240v; all I know is that a 65 Amp alternator handles my 1500W invertor no probs although it would be a good idea to get two spares batteries wired in parallel and fed by a trickle charge. This would power an invertor attached to the batteries by jump cables for most purposes.

OK, just to oblige. Power is volts times amps. So 800 W is 240 V times 3.3 A. But 800 W is also 12 V times 67 A. So if the drill is running at full power, at least 67 A is coming from the 12 V battery. Now if the alternator is not putting out 67 A, the battery is being drained. If the alternator is not running, the battery is being drained very fast. It might even be damaged with that kind of load on it for more than a short time.

So a 65 amp alternator is actually not able to handle a 1500 W inverter at full power, since 1500 divided by 12 is 125 amps. You are saved by the fact that the inverter rarely runs at full power, the battery can take up the slack, and you only run the inverter for short periods. If you tried to run the inverter at full power for a long time, you couldn't do it.

Even the power rating of a drill is misleading, though. If a drill says 800 W, this is the maximum power it can take. It will only use 800 W if you put a heavy load on it. If you only use it for light drilling, it will take somewhat less than 800 W.

All of the above explains why you can use the 1500 W inverter with no problems. Hope this helps.

[79commando]

Cheers MrB you have inverted me and I am now a believer!

[toomush2drink]

Considering the amount of amps being drawn another consideration to think about is the leads you use to connect it to the battery. More amps mean that the wires will get hot quite quickly if they are not up to the job and could cause the dreaded fire. When i get my invertor intend to wire it in with an amp wiring kit for car stereos. These are about £20 and connect direct to the battery with an appropriate fuse just off the battery. In my mind this a safe way of connecting it up and one that is proven with large cat stereo systems with a lot amplifiers drawing big currents. If you wanted to take it a stage further you could install a second battery in the back of the van that is charged by the alternator also. This is called a split charge system and another setup from the world of car stereo.

What ever you decide to do at least make sure you run it direct from the battery with at least one fuse in the system.

[Peaky]

With inverters it is all about the sine wave and what you are wanting the inverter to power,

All the cheap inverters on ebay are totally fine for charging drill batteries etc but should not be used to run motor equipped devices as prolonged useage will destroy the inverter as you are asking too much of it, basically any inductive load will destroy them.

A soft start inverter is illegal to sell in europe and new regs are being brought in this year to stop their sale in the uk as well,

The type of inverter to watch out for is a PURE SINE WAVE one, these are more expensive but means you will have a true mains emulater and would allow you to use any mains operated item.

ALL the types on ebay to date, are modified sine wave inverters and will not handle inductive loads, and can destroy certain electrical equipment.

Maplins although good for a few circuit components are mostly very dear on things like this and the most suitable inverter they sell is £499.99 N91AA and is rated at 1500W continuous power, 2000W peak,

Maplins are non skilled staff, it is a complete waste of time asking them anything technical or anything that isnt written in their catalogue for that matter,

The best system to use is to get a big battery and install it in your van, install the inverter above it and mains sockets next to it, go to a caravaning shop or use Maplins and get a dual battery charger, this will let your van battery charge back up after starting it then start putting power in to your extra battery as well, your alternater shouldnt need changing and definatley wont need changing if you have a diesal, if you dont want an extra battery in your van using the engine battery is totally fine but you will have to leave your van running whilst the inverter is swiched on.

Remember an inverter is a lot quieter at 3am than a generator (unless your spending well over £1000 to get a silent one, powerful enough to power your tools)

[Peaky]

Dam, Toomush you posted as i was typing,

A car stereo kit would be dearer for the correct size wire than going to Maplins and buying the proper gauge (car stereo kits at £20 use 8awg and you should use 4awg) 4awg is around £2.49 for 1/2 M, a fuse should be within 12" of the battery and the earth SHOULD NOT come from the battery, instead it should come off the chassis or bodywork next to the inverter keeping the earth wire no more than 18" long.

[chubby007]

Totally agree with you about Maplins, I have an auto-sparks lined up for the installation and am now on the look out for an appropriate inverter. There are some on e-bay that look big enough (2000w) but are sold from Tiawan, seems a bit risky, I'd rather get one from over here, at least I can take it back! Thanks again for everyones help.

[NKT]

Wow, a lot of stuff on this thread...

If you get an inverter you will probably fry it unless it is rated to three times the power of the drill.

When you start an electric motor, there is a split second where the (theoretical) current draw is infinite. This is because what limits the current through a motor is the back EMF from the coils, which increases the effective resistance from the coils from about .2 ohms, right up to several hundred ohms. It is this initial surge and back EMF that can kill your inverter when the drill is stopped (as the drill spins down, that energy is turned back into electrical energy)

Also, if you are drilling a big hole, you will draw a lot more than the rated power of the drill, which is normally given as a "no load" rating. Motors under stall don't have the EMF any more, so the current goes up dramatically, killing the inverter dead.

For info, 20A is the max you can pull through a ciggie lighter, and that is only [EDIT: Corrected - see below! Ta, MrB!] (20A x 12V =) 240W if it is perfectly efficient. At 240V, (2400W / 240V =) 1 Amp. Figure the inverter and the losses in the wire, and the fact that battery voltage drops fast (and so current has to rise to keep the wattage the same) under those loads, and you will get about 0.8 amps max. A 0.3 amp drill will be ok, but nothing more! (you will have fun finding a 0.3A drill)

So, get yourself a big inverter. I killed mine using a standard little drill, but fortunately the internal circuit tripped from the heat, so it still works ok. Wire it direct to a big battery, keeping the wires to the inverter as short and thick as possible - think how hot jump leads get, and then you are about right! That heat is lost power.

Best idea might be a 1 hour charge 24V drill with two batteries - JCB have one at Makro, £79+VAT - and wire the charger to the inverter. If you want to do that, make sure you get a "pure Sine wave" type.

[MrB]

For info, 20A is the max you can pull through a ciggie lighter, and that is only (20A x 12V =) 2400W if it is perfectly efficient. At 240V, (2400W / 240V =) 10 Amps. Figure the inverter and the losses in the wire, and the fact that battery voltage drops fast (and so current has to rise to keep the wattage the same) under those loads, and you will get about 8 amps max. A three amp drill will be ok, but nothing more!

Whoops! I think you accidentally got an extra zero there.

Here's with corrected arithmetic:

For info, 20A is the max you can pull through a ciggie lighter, and that is only (20A x 12V =) 240W if it is perfectly efficient. At 240V, (240W / 240V =) 1 Amp. Figure the inverter and the losses in the wire, and the fact that battery voltage drops fast (and so current has to rise to keep the wattage the same) under those loads, and you will get about 0.8 amps max. A 0.3 amp drill will be ok, but nothing more!

In short, a ciggie lighter is a no go. If you use an inverter at all for power tools, you need something big and properly wired in. As others said, the ideal setup is a dedicated heavy duty battery located close to the inverter and connected to it with nice thick wires and heavy duty connectors. Then run a secondary charging circuit from the alternator to the inverter battery (again, with heavy duty wires).

From the battery to the inverter you probably want to be using maybe 4 AWG, and from the alternator to the battery maybe 6 or 8 AWG.

See here for a table of allowable amps vs wire gauge:

http://www.powerstream.com/Wire_Size.htm

Remember you need to allow for currents of 60 to 100 Amps.

Remember especially that 60 to 100 amps in thin wires equals red hot metal, melting plastic, smoke and fire!

[NKT]

MrB,
Oh shish kebab! You are right... I've gone back and corrected. Good that I can edit here - shame we can't on some other topics Anyone know why?

And 60 to 100 amps in even thick wires means "ouch!" if you touch them. Don't ever use a "dry cell" lead acid battery, either, as it will probably melt (yes, I have, it was a right mess!) unless you spend hundreds on a big one, and you will get hydrogen outgassing from even a sealed Lead-Acid battery at these current draws.

[Peaky]

Actually you can pretty much try and take what you want from a dry cell (within reason) and it shouldnt get damaged, they get damaged from people using the wrong charger!! a car battery charger will blow them up after only a couple of charges if that, the proper charger should be used, You can get car battery sized dry cells that run off your standard alternator and will easily cope with the power you would draw from them, they arnt much dearer than a good quality battery anyway. 4AWG is the thinest wire i would dare use on any part of the wireing for it, anything smaller and you are taking a risk, when i used to do competition cars for stereo comps i used 0 gauge quite regulary for the power feeds then 4 gauge for all the interconnecting in the boot,

[BUNGYSTRAP]

I have just fitted a 600w inverter in my van which is ample to run my key machine as this is the running rating and has a soft start facility. Most inverters also have low voltage detection which stops you completely discharging your battery. One thing to note is that if your invertor comes with cables for connecting to the battery, they should not be extended/lengthened. Instead you can run an extension lead from the 240v output. This is due to their design and voltage drop. Another valuable addition to the plethera of tools is a small whisper quiet generator like the one screwfix has. Only 720w but only £99 and ample for lighting / keycutting and battery charging. Small enough to store in the van and available in times of termoil.

[hzatorsk]

I've read this entire thread and have nothing useful to add.

It seldom happens... but I thought you all should know!



hzatorsk