Run Charger off Inverter?

Submitted: Sunday, Apr 26, 2009 at 19:05
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There was a post the other day that touched on this, got me thinking about it. Have a few questions:

Is Inverter a viable alternative to a generator?
Can a 25-30amp 3-stage charger (or say 25 amp ctek) run ok off an inverter?
If so I calculate at least a 500w inverter would be needed – is that enough though? If not what’s needed?
Is pure sine wave needed to run a charger safely or is modified wave inverter ok?
For this charging option I would take supply direct from battery terminals. Are there any traps – can only think of fuse / wire size, battery damage perhaps?

Thanks in anticipation.
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Reply By: Best Off Road - Sunday, Apr 26, 2009 at 19:20

Sunday, Apr 26, 2009 at 19:20
Kym,

I'm making an assumption here that you are suggesting idling the car, to power the inverter, to in turn power the charger to recharge the battery.

Surely (and I could be way off the mark) using the alternator direct to the battery would be more efficient.

The only problem with this whole scenario is that alternators at idle do not put out sufficient current. Oh for the days of the hand throttle (a la GQ) when you could screw the the revs up to 2000 to 2500 and get the alternator working.

No idea if I am right or wrong but just some thoughts.

Robin Miller has some actual engineering expertise on such matters and will hopefully advise.

Cheers,

Jim.




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Follow Up By: jdwynn (Adelaide) - Sunday, Apr 26, 2009 at 19:53

Sunday, Apr 26, 2009 at 19:53
Sorry Jim, I didn't outline the whole thing properly. The charging I'm looking at is for camper batteries, from car battery. cheers
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Reply By: ctaplin - Sunday, Apr 26, 2009 at 19:23

Sunday, Apr 26, 2009 at 19:23
It would work with the correct sized inverter but why would you convert 12v to 240v and then back down to 12v to charge a battery considering that inverters are not anywhere near 100% efficient?
Eg, you would need a decent charge going into the battery powering the inverter in order for it to run the charger. Seems a pointless exercise to me...
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Follow Up By: Nomadic Navara - Sunday, Apr 26, 2009 at 19:28

Sunday, Apr 26, 2009 at 19:28
Simple - a three stage charger will charge your battery at a much higher voltage than a direct connection to the tugs alternator. The higher voltage tailored to the battery will charge the battery much quicker.

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Follow Up By: Gronk - Sunday, Apr 26, 2009 at 19:52

Sunday, Apr 26, 2009 at 19:52
Yes, but say the batt is down to 12V, how long will you have to idle the 4x4 ?? 1, 2 or 4 hrs ??
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Follow Up By: jdwynn (Adelaide) - Sunday, Apr 26, 2009 at 19:55

Sunday, Apr 26, 2009 at 19:55
Sorry chaps, as for response to Jim above, the charging I'm looking at is for camper batteries, from car battery. cheers
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Follow Up By: Brian (Montrose, Vic.) - Sunday, Apr 26, 2009 at 19:59

Sunday, Apr 26, 2009 at 19:59
Would iy not be easier just to hook the CT up to the 4wd with your standard 12 power connection with a battery isolator etc in line and charge the batteries that way? Or am I missing something too?
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Follow Up By: jdwynn (Adelaide) - Sunday, Apr 26, 2009 at 20:14

Sunday, Apr 26, 2009 at 20:14
See, trying to keep the thread short and to the point was a total failure.

It's been well discussed on EO that alternator flow gets regulated by temperature or otherwise down to a fairly small amperage (?10-15 amps). So devices like Ranox or Arrid Twin Charge pump up amps or voltage - Ranox to about 25amps. So I thought this option might be a way of replicating what a Ranox does but give more flexability.

Associated thing is that I've had 2 experiences lately where being able to charge another car or another peron's camper batteries would have been helpful. So again this option got me thinking.
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Follow Up By: Nomadic Navara - Sunday, Apr 26, 2009 at 20:32

Sunday, Apr 26, 2009 at 20:32
jdwynn

Your idea of an inverter/charger will do the same job as the RanOx. It will be a fair way to go if you already have the charger but cast a hell of a lot more for the same quality equipment if you have to purchase both from pieces.

I don't consider the Twin Charge in the same league. It does not have a three stage output. It only has a fixed 14.5 V OP. I attribute one of those units for the demise of the first battery in my present van.

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Follow Up By: Member - Chris & Debbie (QLD) - Monday, Apr 27, 2009 at 00:03

Monday, Apr 27, 2009 at 00:03
I would also recommnend the RanOx, Fitted one not long ago and are a fantastic piece of equipment. Three stage charger where you can set float voltage, max charge current up to 25amps. Can be configured to control various relays including low voltage shut off. A handy feature, called, transfer mode, will allow you to charge your camper batteries from your vehicle battery if you have been away from camp on a day trip.

Chris
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Reply By: Roughasguts - Sunday, Apr 26, 2009 at 20:02

Sunday, Apr 26, 2009 at 20:02
Interesting but I think I would get a 99 dollar generator from the now defunct GMC to charge the batteries and run the fridge, your going to use less fuel and do it quicker.

The cheapie generator on 12 volt setting is 7.5 Amps and a tad over 17 volts wich is a worry as it's all over the place and a bit to high for my liking.

But I guess on 240 volt it could run the charger at a better Amp output or at least what your charger puts out.
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Reply By: Peter McG (Member, Melbourne) - Sunday, Apr 26, 2009 at 20:17

Sunday, Apr 26, 2009 at 20:17
JD

I think the ARRID 12v charger would be the best option.

ARRID charger

Cheers

Peter
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Reply By: Member - Phil G (SA) - Sunday, Apr 26, 2009 at 20:24

Sunday, Apr 26, 2009 at 20:24
If you look up the Ctek manual here, it says you need 2.9Amps at 240V. That suggests you'll want at least a 1000watt inverter and theres no guarantee that that would work.

I did the calcs for my 300watt inverter some time back and figured the biggest charger I could run would be a 7 amp Ctek.
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Reply By: Peter_n_Margaret - Sunday, Apr 26, 2009 at 20:50

Sunday, Apr 26, 2009 at 20:50
What you propose is done.
It makes particular sense if your camper batteries are a long way from your crank battery. The voltage drop in the 240V is insignificant, wheras to run 12V direct may need massive cables to maintain a decent charge rate.
Also, the charger can be much more sophisticated than an alternator, get a better rate of charge, be properly set to charge AGMs or Gels at the best voltages for boost, to float and therefore give you better battery life.
And the inverter is very useful for other stuff too.....and silent.

Cheers,
Peter
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Follow Up By: Nomadic Navara - Sunday, Apr 26, 2009 at 20:58

Sunday, Apr 26, 2009 at 20:58
This again raises the dangers of running 240 V between two vehicles and whether you need a licensed electrician to wire the installation. It is much safer to run heavy cable, locate the inverter next to the charger and plug the charger directly into the inverter. If you are going to install the inverter with an extended cable installation you need a licensed tradesman.

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Reply By: ABR - SIDEWINDER - Sunday, Apr 26, 2009 at 22:29

Sunday, Apr 26, 2009 at 22:29
This can be done. It may void warranty on the charger and inverter and also be a concern with a number of safety issues if tried while towing and trying to charge the towed vehicle with 240V. In this instance I recommend 12V to the towed vehicle and not 240V.

I did a test last year using a small 15 Ah battery charging a 60 Ah wet cell battery.



I in no way recommend this method but am asked quite often if it will work.

Regards

Derek from ABR
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Follow Up By: Boobook2 - Monday, Apr 27, 2009 at 11:57

Monday, Apr 27, 2009 at 11:57
Derek, as a matter of interest, did you measure the current from the source (11.93V), and the charging ( 14.1V) batteries? It would be interesting to see the efficiency in watts.


BTW I assume this product does the same thing without 240V
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Follow Up By: ABR - SIDEWINDER - Monday, Apr 27, 2009 at 17:47

Monday, Apr 27, 2009 at 17:47
No exact measurements done but recall about a 3 amp difference. IE: Inverter 13A load and Charger 10A Output. This would equate to about 85% efficiency on each device.
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Reply By: jdwynn (Adelaide) - Sunday, Apr 26, 2009 at 22:38

Sunday, Apr 26, 2009 at 22:38
thanks all, responses much appreciated
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Follow Up By: Bonz (Vic) - Thoughtfully- Monday, Apr 27, 2009 at 10:22

Monday, Apr 27, 2009 at 10:22
jd you can buy a dedicated 12v charger, with a little honda motor that just outputs regulated 12v.

What you are suggesting will work, but is hugely inefficient. If you look at it like this. Energy is happy being in one medium, say a 12 v battery. To make it change state, like change to 240v then back to 12v, makes it do work and it doesnt like that so it frets a bit and loses some of that energy fretting. It will do it in the end (change its state) but you'll have less energy at the other end due to the fretting.

Same deal with an engine, petrol to motion, lots of fretting, motion to electricity (via an alternator), more fretting, alternator (AC power) to DC power to charge your battery, a little more fretting.

Every time you ask energy to change its state it loses some, and you can see this as heat (as in an engine), or slipping belts (as in an alternator, and in the end you will have less of it.

For my money if I wanted to use the car to charge the camper batteries, I would throw a lead from the alternator to the camper batteries and run the car directly charging the batteries, or setup the batteries so you can pop them in the car when you take a drive, and hook them up to charge that way.
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Follow Up By: ben_gv3 - Monday, Apr 27, 2009 at 12:35

Monday, Apr 27, 2009 at 12:35
Bonz;

This Honda 12V generator you speak of. As it outputs 12V, it's not enough to adequatley charge a bettery, which needs up to 14V (13.8V I believe).


As said before the OP may have limitations as to locating the caravan batteries close to the tow vehicle, and whilst more inefficient I can see a benefit in having a big inverter since it can be used for other purposes not just charging batteries.

I am curious to know just how inefficient this setup would be. As eluded to Derek's experiment above getting 11.93V is pretty poor when the source battery is at 14V.
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Follow Up By: Bonz (Vic) - Thoughtfully- Monday, Apr 27, 2009 at 13:13

Monday, Apr 27, 2009 at 13:13
Ben you got Dereks setup backwards, its 11.93v in and 14v out but its the efficiency thats a killer.

A good solid state inverter runs at about 85% efficiency but may runs down as low as 70%.

A Ctek charger efficiency is about 85% also, so here you have a multiplying effect, and you could also add in the losses from connections and wiring etc ((i reckon 2-3%)

so if you want say 10 amps into the camper battery, then you'll need to drag 13.84 amps out of the car battery not allowing the losses in connections etc.
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Reply By: Sobriquet - Monday, Apr 27, 2009 at 14:54

Monday, Apr 27, 2009 at 14:54
I assume efficiency is not much of an issue if eg the battery being charged is in a camper and you are charging it whilst driving your car. I assume Its about avoiding the voltage drop from car to trailer which means you will never get a full charge.

If you already have the charger or the inverter its a cheaper way to go than buying a 12v-12v charger, which tend to be very expensive for the kind of amperage you mention.

The inverter will happily cope with the voltage drop from vehicle to trailer, so you will get a full charge. I think its a good idea. I've been thinking about doing myself for some time now.

You would obviously put the inverter/charger next to the battery being charged - keep the live 240 wiring to a minimum.

Thoughts on whether you need pure sine wave or not. I bought a modified sine wave inverter years ago and found it useless for charging phones and cameras - retired it to the shed and bought a pure sinewave for them. So probably a smart charger may need the same.

I suspect square wave power can affect some power circuitry making it run hot and inefficient (anything more sophisticated than a good old fashioned transformer). My phone charger ran really hot and put hardly any charge into the battery.

Runinng a 25amp ctek would require at least a 500w inverter - might be running near its limit - i.e hot - so probably one size bigger might be better. If you need pure sinewave that would get expensive.

10 amps at 12 v is 120watts, so I would ve thought for anything up to 10amps a 250w inverter would be ample. Perhaps consider sticking to that
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Reply By: Ianw - Monday, Apr 27, 2009 at 19:59

Monday, Apr 27, 2009 at 19:59
I have just wired my van up with this system. Have used 3B&S wire from car bat to junction box in van. Using "trip switches" (thanx Derek!) am able to charge battery in normal fashion, i.e. directly connected, or am able to switch 500w inverter on to power 15amp 3 stage charger. Also run 3 way fridge at full 14+V and hopefully will operate to max efficiency. Am leaving on 8 week trip north next week so will give it a good tryout.


Ian
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