Charging 3rd battery with 240v charger while driving

[Dirt devil]

I am looking to recharge my 3rd battery while driving and as I have a redark BC - DC charger for the 2nd battery it struggles when the third battery is hooked up.
I looked at the Ark ac-dc charger, looks good but only 5A charging.
My thoughts are, as I need to buy an AC charger anyway, what would be the problem using this via an inverter( I have a 500w and 1500w already) while driving? The plus for this is I could use a multi stage charger and then use same when I need to put the batteries on charge at home every 3 months.
All my batteries are AGM and 110amp, so looking at getting around the 25 amp ac charger.

cheers Shane.

[megatexture]

Could always look at replacing the redarc with a ctek 250 dual and also run the smartpass that will give you 80amp of multi stage charging suitable for charging up to 800ah of battery capacity.


http://www.baintech.com.au/marine/ctek-smartpass-energy-management-unit

The only downside will be you would need to purchase both the 250 dual and the smartpass and last time I looked would be around 500$

[04OFF]

So you want to convert 12V power to 240V, then convert the 240V power back to 12V ? :eek:

[Dirt devil]

Thanks for the replies,
"So you want to convert 12V power to 240V, then convert the 240V power back to 12V ?"

I was just asking a question, as said on this forum may times, an alt. will not charge an AGM to its max. so this was an alternative as I am going to buy an ac charger anyway.
As I have already the Redark BC to DC charger it should show you I have done the right thing with my 2nd battery and now need a 2nd fridge for a trip and this needs its own battery so this was my reason for the question. If it was a permanent thing I would buy a 2nd BC to DC charger.

cheers DD.

[Drewboyaus]

I run a Redarc SBI12 under the bonnet to charge my two batteries up front. I also rigged up a removable third battery setup with an ARKPak and CTek D250S. I Velcro the CTek to the top of the ARKPak and have made up some looms with Anderson plugs to connect it all together to the alternator when in the vehicle. The ARKPak runs a 120Ah AGM and the beauty of the setup is that I can take it out and leave it at camp with the fridge hooked up to the solar (the D250S also acts as a solar regulator).


46328

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[megatexture]

You would need to use the 1500w inverter as you would need 696w to run the charger (ctek25a) so at that would be likely More than what your redarc would be putting in off the alternatorand that's assuming the inverter only draws off the current that's needed to use the charger. http://www.redarc.com.au/handy-hints/-/inverter_current_draw

Can you put a switch between the batteries to isolate one to allow them to charge one at a time? So you can use one while the other charges or solar on a roof rack to boost things along? As you said its not a permanent thing

[04OFF]

I was just asking a question, as said on this forum may times, an alt. will not charge an AGM to its max. so this was an alternative as I am going to buy an ac charger anyway.
As I have already the Redark BC to DC charger it should show you I have done the right thing with my 2nd battery and now need a 2nd fridge for a trip and this needs its own battery so this was my reason for the question. If it was a permanent thing I would buy a 2nd BC to DC charger.

cheers DD.

I was just asking asking a question too Shane, hoping you could confirm I was understanding what you were saying correctly, as a transition from 12 to 240 then back to 12 using such a large inverter etc, comes across as very power UN-efficient (not saying it is, that's just how it reads) :smile:

[Cuppa]

Using an inverter running off the crank battery to charge an auxillary battery was a standard practice in the motorhome environment prior to the advent of dc to dc smart chargers. It is an effective means of charging the aux batteries & only has one pitfall & that is that you have live 240v runing through the cable between the inverter & charger whilst mobile. In the event of an accident there is a risk that were this cable to sustain damage & touch against the metal of the car that the SES chap who comes to pull you out of the wreck could be electrocuted. However the ‘standard’ practice to reduce this risk to almost negligible level is to ensure that the cable between inverter & charger is as short as possible & routed to avoid any possibility of contact with metal.

For a 110amp battery I think a 25amp Ctek charger would be overkill. Much cheaper to buy a smaller (say 7 or 10 amp charger) & let the alternator do the bulk charging, then switch over to the smaller inverter (use the 500amp one seengs you have it, but potentially could go smaller) to top up the battery once it had reached about 75% full (say after perhaps an hour or so of driving - mor or less depending upon how much it had been discharged). Just needs a switching arrangement to change from direct alternator charging to powering the inverter. Need to know how to set up the switching to avoid damage to the alternator. I’m not cetain, but I think the switch needs to be a ‘break before make type’ (3 way on/off/on) - perhaps Yendor or others might comment on this.

There are some arguments about the efficiency of converting 12v to 240v to 12v, but as you are driving & running the alternator anyway the degree of inefficiency isn’t going to be big enough to show up in your fuel consumption.

[Bloodyaussie]

I run 3 batteries and after some advice from Piranha 4x4 is working perfect... I had it wired wrong before and was getting charging issues and constant flat batteries but after there advice have the 2 aux batteries running parallel and things are working perfectly.. I also run a large inverter off the aux and get so much run time with it including running a fridge through it for days...

[Dirt devil]

Thanks again for your replies, there is some good advice given and will take it on board.
I do like the info from Cuppa and was on the lines of what I was thinking of and as I am going to buy a 240v charger anyway seems the most cost affective.


cheers DD.