Power inverter for my van

[Phill Peck]

Hi I have ordered an inverter for my van it's 2000w peak 1000w cont rated. Can anyone advise what gauge/size of cable it will need to connect to the battery. Will be about 2.5 m if that's relevant

Thanks[/b]

 

[westie101]

So that equates to at least 166 amps peak and 83 amps continuous at 12 volts, I would think the first thing you need to do is check the rating of the alternator on your van as those loads will possibly overload it leading to a flat battery in very short time

Inverter Efficiency

By efficiency, we are really saying, what percentage of the power that goes into the inverter comes out as usable AC current (nothing is ever 100% efficient, there will always be some losses in the system). This efficiency figure will vary according to how much power is being used at the time, with the efficiency generally being greater when more power is used.
Efficiency may vary from something just over 50% when a trickle of power is being used, to something over 90% when the output is approaching the inverters rated output. An inverter will use some power from your batteries even when you are not drawing any AC power from it. This results in the low efficiencies at low power levels.

A 3Kw inverter may typically draw around 20 watts from your batteries when no AC current is being used. It would then follow that if you are using 20 watts of AC power, the inverter will be drawing 40 watts from the batteries and the efficiency will only be 50%.
A small 200W inverter may on the other hand only draw 25 watts from the battery to give an AC outpur of 20 watts, resulting in an efficiency of 80%.

Larger inverters will generally have a facility that could be named a "Sleep Mode" to increase overall efficiency. This involves a sensor within the inverter sensing if AC power is required. If not, it will effectively switch the inverter off, continuing to sense if power is required. This can usually be adjusted to ensure that simply switching a small light on is sufficient to "turn the inverter on".
This does of course mean that appliances cannot be left in "stand-by" mode, and it may be found that some appliances with timers (eg washing machine) reach a point in their cycle where they do not draw enough power to keep the inverter "switched on", unless something else, eg a light, is on at the same time.

Another important factor involves the wave form and inductive loads (ie an appliance where an electrical coil is involved, which will include anything with a motor). Any waveform that is not a true sine wave (ie is a square, or modified square wave) will be less efficient when powering inductive loads - the appliance may use 20% more power than it would if using a pure sine wave.

So if efficiency is 90% at full load that means 184 & 92 amp

 

[timtheenchanter]

http://www.solar-wind.co.uk/cable-sizing-DC-cables.html

seems to recon on 25mm sq, if your running the 12V down there, it does work out at about 83A, quite a bit.

damn, beaten to it.

The couple of guys I know who have that sort of inverter power in their vans, have a split charge system, with a couple of 110AHr leisure batterys in a box in the back of the van (one each side of the wheel arch, then boxed in)

 

[Phill Peck]

Thanks for the advice

It's going in for new brakes tomorrow so I'll ask about the rating of alternator

I want to run a compressor and charge batteries etc so maybe I've over spec'd the inverter was just thinking it would be better to have more than I needed rather than running at full capacity. Bad idea?

 

[timtheenchanter]

check the rating of the compressor, some can have deceptively high start up draw.

 

[RF Lighting]

I've got a small invertor in my van charging the drill etc, ant even a small invertor will quickly drain your battery.

As has been mentioned, I've put in a split charging system and a dedicated ~75Ah battery for the invertor and some additional lighting.

 

[Phill Peck]

check the rating of the compressor, some can have deceptively high start up draw.

The compressor is 300w but no mention of start up load

 

[Phill Peck]

I've got a small invertor in my van charging the drill etc, ant even a small invertor will quickly drain your battery.

As has been mentioned, I've put in a split charging system and a dedicated ~75Ah battery for the invertor and some additional lighting.

This sounds like a good idea could you elaborate on the split charging system

 

[RF Lighting]

Basically when the engine is running the two batteries are in parallell and both get charged. When the engine is stopped the starting battery and the leisure battery are seperated by a relay so auxilary power is only drawn from the leisure battery leaving the starting battery fully charged to turn the engine over.

There's loads of diagrams on t'web, especially on caravanning sites.

 

[333rocky333]

i have a small 300 watt invertor that plugs in the lighter socket, i use it to run a 28watt 2d fitting when need be, within an hour battery is flat and unable to start van, so now i have to leave engine running to use it

 

[ericmark]

Ran a 3.5kW 12v inverter in a narrow boat it was hard to run correct size cables round the bends so we used 2 x 35mm cables not really big enough but did the job.

The batteries again not really big enough we used one for engine starting and three for inverter all ratted at 180AH so there was 540AH for the inverter.

The alternator and charger was also a problem. The step charger was only 35A although it would recharge the batteries it was right on the edge for that AH ratting as the current at which the charger drops voltage becomes higher as the AH ratting increases.

The alternator two 120A were set one to engine battery and the other to the inverter batteries and again the inverter alternator should really have been connected through a pulse step inverter charger or at least using a special regulator giving step charging but in fact it was a normal regulator. Even so they did get rather hot.

OK your inverter is not as big as the one we had but clearly you will need a large traction battery able to stand deep cycle not a vehicle battery I would say no less than 200AH. To recharge this in for example 4 hours one can't even consider anything but a step charger and since the vehicle may not like the 14.8 volt it will either need a second alternator or an inverter to do the charging.

Something like the A to B Sterling charger will be required to recharge the batteries within a reasonable time. I would be considering at least 2 x 110AH batteries.

A normally alternator charges at around 13.2 - 13.8 volts and the idea is that only during starting will the battery be drained and float charging will be good enough. Although the alternator may give out 80A the battery will soon rise in voltage so will not take much charge even though it's still only 60% charged. So with step charging there are normally three stages at first flat out charge until 14.8 volts is obtained and then it keeps that voltage (stage 2) until the amps drops to around (according to setting) 5A at which it senses the battery as charged and drops the volts to 13.2 to stop over charging. Using this method a battery which would with standard vehicle alternator would take 10 hours to charge will likely charge in around 4 hours.

With the boat we would monitor the SG of the batteries and if low would refrain from using the inverter. But with 540AH if the batteries were down to 20% one could be looking at a weeks cruising with engine running 8 hours a day to return them to just 80% charged. Clearly for you that will likely not be good enough so unless you use something like the A - B digital charger I have linked to then the batteries are likely to sulphate and it will cost you dear in replacement batteries.

Overnight charging is another option but step battery chargers from the mains are not cheap either.

 

[ban-all-sheds]

i have a small 300 watt invertor that plugs in the lighter socket, i use it to run a 28watt 2d fitting when need be, within an hour battery is flat and unable to start van, so now i have to leave engine running to use it

Hmm - not sure that 3-4A for an hour should do that to a battery.

 

[ericmark]

Today vehicle batteries are quite small so with losses yes I can see a 2D lamp discharging the battery to a point where the vehicle will not start.

Before the pulse monitoring step charger hit the market we had two common methods of split charging.
1) The blocking diode was considered the best but the 0.6 volt drop meant that one needed to move the spade connector to Hi on the CAV 440 regulator and cheaper charging systems did not have that option so.
2) The split charging relay was the more common method. Theory there was nothing to stop the fully charged battery from discharging into the flat battery as the relay contacts closed but in practice with batteries of under 80Ah there did not seem to be a problem.

The idea was two fold first it would not discharge the engine battery and second it would not try to draw starting current from the aux battery.

There were two methods used.
1) The ALT output from the alternator would close the relay and since the alternator would not charge until the engine was running this worked well but then some alternators did not have a ALT terminal with 12 volt but used some other method like the star point.
2) Some ignition switches turned of the auxiliaries when in the start position so this supply could be used instead of alternator connection.

Both methods of split charging needed the batteries to have thick short leads specially with diodes leads needed to be same lenght.

On the old Lucas alternators the replacement diode pack had diodes for the warning light the same size as the main ones so by adding three extra diodes to work the warning lamp and regulator then the original diodes could be used to charge a second battery. This worked very well and I have even installed link bars so I could use small van to jump start 24v with this charging method there was no chance of short if links not returned to 12v mode.

But the battery to battery chargers and A - B digital chargers have superseded all this and today it's easy.

 

[Lectrician]

I have a small true-rms inverter, only around 450w I recall. As my battery is under the footwell, there is only a short 1m or so of cable, and 6mm does the job nicely.

I used a relay to allow the inverter to only work when the ignition is on, as even charging batteries it is surprising how quickly a battery will die.

TBH, it was something I thought I would use all the time, but rarely do these days!

I find the only times I use it is when I end up needing to use my satellite or terrestrial signal meters with out warning, which are both charged by the mains, and both always flat when I come to use them! Plug them both is as I drive to the job.

I opted for a True RMS version as I had issues in the past with electronic battery charges and inverters/portable generators. However, it seems others have had no issues! If you can stump up the extra money, True RMS would be the way to go.

 

[Phill Peck]

right my compressor is 300w and i will only use when the engine is running
it is only 4.5 litres so only takes about 3-4 mins to charge vessel which is enough for each job

should i order a 500/1000 inverter instead?