Adding a DC-DC Charger to the Tvan

[Frankrhona]

Locked down in Greater Sydney it was time to start another project...fit a DC-DC charger to the Tvan seemed like a good idea.
So I compared the Redarc BCDC1225D, the Ctek D250SE and the Renogy DCC30S, all with Solar inputs, and decided on the Ctek for a couple of reasons. 1. I already have a D250 under the bonnet for the Auxilliary battery that has served me well for 10 years and 2. it is more compact and fitted the space better.

I located it in the front section of the storage locker, behind the retrofitted tent pole tube and close to where the wiring ran from the cabin to the battery. Re-wiring involved moving the Anderson feed from the battery to the input side of the charger. Then I pulled all the wiring from the battery to the cabin back into the locker, including the 30Amp Fuse. Next I ran new feed from the output side of the charger to the battery. I fitted the 30 Amp Fuse holder beside the charger and connected it to the output, (battery). I ran 6 B&S twin from the 30A Fuse to the Power Box and 240V charger. Then I disconnected and removed the Solar controller and connected the Solar panel directly to the Solar input on the charger.

Now you would think job done! But NO. I needed to change the feed in the vehicle.

Pre-charger this is what I used to do and still wished to do. With the Fridge in the back of the vehicle, when camped up I would connect an extension between Anderson plugs to parallel the Aux battery and the Tvan battery to keep the beers cold. But, all the literature from Redarc, Ctek and Renogy have the feed to the "trailer" DC-DC charger from the Start battery, not the Aux battery. Why? Because the Dual battery DC-DC charger maybe in float mode for the Aux battery whilst the Tvan DC-DC charger maybe in Bulk mode and be actually draining the Aux battery or any other combination. The bottom line is if you want the best results DC-DC chargers need to be wired in parallel NOT series. So, I changed the Vehicle Anderson plug feed from the Aux battery to the Start battery.

Am I happy with this? NO. Why, because someone who does not know the set up could inadvertently plug a load into the Anderson plug and drain the Start battery. Secondly, I now connect the extension lead between two Anderson plugs, one on the Aux battery and one on the Tvan battery when in camp. At some time in the future I may connect a Redarc SBI or similar between the start battery and the Anderson plug.

And I initially thought it was just a simple fit a DC-DC charger project! Thankfully, time is meaningless in lockdown.

Cheers, Andrew.

[Ray]

Thank you Andrew for giving us something to think and write about, been very quiet on the forum

1. Does the ctek reserve power for starting eg only supplies power when voltage shows there is a charge source connected (alt or solar)? If so what you have should work ok.

2. I have also modified the tvan by adding a renogy lithium battery and heavier cable from battery to distribution box. I used circuit breakers instead of the 30 amp fuse because I have read that a fuse can allow current slightly above the fuse rating without blowing and this can overheat  cables, the c/b has both short protection and heat protection and protects both cases, so the theory goes.

3. My general approach has been different, I use 2 victron 100/20 solar regulators where you have dc-dc and all batteries are connected together to share charging currents and supplying loads. Mostly the tvan stays unconnected and looks after it's own needs quite happily and the 300 watt panel on the vehicle runs the fridge from aux battery (and start battery if needed). The bluetooth monitoring via smartphone is a bonus.

[Frankrhona]

Hi Ray, good to hear from you.

To answer your question yes, The D250SE for a conventional alternator has a cut-in voltage of >13.1V for 5seconds and a cut-out voltage of <12.8V for 10 seconds. For a Smart alternator they are >11.8V and <11.4V respectively. The back current drain is less than 1Ah/month which is insignificant.

I am happy with the single 105Ah AGM battery in the Tvan considering we run minimal loads: a few LED lights, a Sirocco fan occasionally and the water pump for washing up only. I now have a 105Ah Fullriver under the bonnet to run the fridge. Made a custom heat shield to surround it on the engine side to keep it as cool as possible. Seems to be OK and it can run the fridge overnight. The 105W Solar panel does a pretty good job of charging it, but 300W would be better!

However, needing more projects I purchased an EvaKool TMDZ70, a 61 litre dual zone to replace the Engel MT45FG single zone. I was very happy with the Engel, it never missed a beat, but was a hassle when running it as a freezer on remote trips and using an Techni-ice esky as a fridge. Thought about getting an Engel MD27 as a second fridge, but the cost, (if you can get one), is about the same as the EvaKool and the power requirements nearly double, (with 2 fridges). The specs for the EvaKool and the Engel are similar, 2.4Ah vs 2.3Ah, depending on which brochure you read.

If lockdown persists I will do a side by side test.

Cheers, Andrew.

[geoff_mck]

It is very common practice to isolate the power from the start battery to the rear Anderson through the fitting of a solenoid triggered from an ignition feed. So when the car is running the solenoid (or heavy duty relay) is switched closed allowing power to feed through to your DCDC in the van and when the ignition is off, the solenoid is opened, isolating the start battery from the rear Anderson. Or have I misread your issue?   

[Frankrhona]

Hi Geoff,

Or have I misread your issue?

Thank you for your feedback. I do not have an issue as such. However, I was attempting to highlight an issue to readers for the need to run two DC-DC chargers in parallel.

Often people fit a DC-DC charger to the vehicle first and run their Anderson plug off the second battery. If you later add a DC-DC charger to the Tvan, as I did, you need to change the Anderson plug feed back to the Start battery and to be safe do as you suggest.

[Phil G]

Gday Frank,
Nice work.  I also run a 10 year old Ctek 250S in the Tvan.  I tested it recently and still working perfectly.  Just a  couple of comments if I may:

The fuses need to be located as close to the batteries as possible.  Otherwise there is no short circuit protection of the cable which is the only reason we fit a fuse. The fuse next to the Ctek is doing nothing.   I've changed out all my maxi blade fuses to the newer style Midi fuses. Much better fuse and easily mounted.  Many DC-DC chargers are supplied with midifuses these days to avoid fuse-related issues.

And yes, you must have a separate dedicated feed directly to the start battery for many reasons.  The DC-DC chargers stop every so often to check the start battery voltage and if they were in any way piggybacked, the sensed voltage can be lower and the DC-DC will cut out and not charge.  Also no point in having DC-DC chargers in series because the current will become limited to 20A for both.  Your Andrerson plug feed needs a 50A fuse at the cranking battery and as Geoff suggests above, you can control the power with an ignition controlled solenoid or a Voltage Sensitive Relay.   But I don't think this is necessary - nobody steals your 12V power, and a relay would prevent you easily charging the car batteries via an anderson plug lead.

Running a cable between Tvan and car is usually done on a powered site - that way you can use the Tvan's 240V charger to top up car batteries.  But to use the lead when not hooked up to 240V doesn't achieve much.  When you join two batteries of different voltages, not  much current travels between them because the difference in voltages is not enough.  And certainly not enough to charge the other battery.

Cheers and keep up with the lockdown projects!