dc/dc charger for my situation

G'day John & Val & thanks for the reply.

I perhaps wasn't clear enough in my initial post. The aux battery is a Bond silver calcium deep cycle & Pin 9 connects back to the aux battery, not off the start/cranking battery, therefore the smart solenoid should (hopefully) still be ok where it is.

I believe the c'van batteries are not calcium.


Not knowing a great deal about dc current, my main concern was that, when driving, the c'van batteries are receiving charge from 2 wires, ie the dc/dc charger (pin 9) & the bridged pins (8 &12). Would this be a problem?.

I am assuming the calcium aux battery will receive plenty of charge whilst we are driving and will not be heavily discharged at any time, even though it does run a 40l engel fridge. The engel runs off a marine grade cig socket that is "live" all the time and connected direct to the aux battery.

The c'van will have a 40 a/h mains charger & the solar regulator will also be 40 a/h (3x135w solar panels on c'van roof).

If I am really stuck, I have a Honda 2.0i generator and a seperate ctec 8 ah portable mains charger & a portable 80w solar panel with 20 a/h regulator that I can connect direct to the vehicle aux battery (when not hooked up/ connected to the c'van).

On reflection, the dc/dc charger may be a bit of overkill !. However, would still appreciate any comments/suggestions.

Hi Ian,

I misunderstood what you propose.

The present arrangement with the smart solenoid connecting the vehicle aux battery to the alternator/cranking battery is fine, and taking a line from the aux battery (ie after the solenoid) back to the van to the input of the dc-dc charger is also fine, but with a proviso discussed below. Connecting the batteries all together using the 8/12 lines and connecting them to the output of the dc-dc charger has big problems.

First - The input to the dc-dc charger MUST be disconnected from the aux battery when the engine isn't running, as otherwise the aux will continue to charge the other batteries through the dc-dc charger. This will call for some device, maybe just a high current relay (eg headlight relay) controlled by the ignition switch (maybe directly off the "accessories" circuit?)

The problems - I think you proposing to connect the van batteries to the auxilliary battery via the 8/12 lines and then to connect them all to the output of the dc-dc charger. If I'm right in this - The 8/12 and 9 lines will all be connected together at the aux battery. The input of the dc-dc charger is connected to the aux battery via the the 9 line (via some switching device to disconnect when the engine isn't running). There is then a direct path via the 8/12 and 9 lines from the dc-dc input to its output, a short circuit from input to output. This will either kill the charger or at best render it inoperable.

What it comes down to is that the aux cannot be simultaneously charged by the alternator as at present AND by the dc-dc charger. Either, but not both simultaneously. I think my preference would be to retain the existing system in the vehicle (it's not broke so don't fix it!), and use a dc-dc charger for the van batteries. I would also use all three wires to carry current from the vehicle to the input of the dc-dc charger, and provide switching in that line to disconnect when the engine isn't running. You will not have aux battery power to the van, but will retain the present vehicle setup and can deliver a good charge to the van batteries.

One final point - we tend to overlook the fact that current flowing in the positive line/s must also flow through the negative lines - ie, the earth return also needs to be pretty robust.

HTH

John

G"day again John & Val.

Seems to be a bit of confusion & probably caused by me. The c'van batteries will be connected to the aux battery by the bridged 8 & 12 pins using a separate line. The dc/dc charger will be installed near the c'van battery bank using a continuation of the no. 9 pin which goes back to the aux battery via a seperate wire , which has a device connecting to the ignition switch so that it only carries current when the engine is running.

The 8/12 pins will not be connected to the dc/dc charger (no. 9 pin) in any way. This should mean that the aux only receives charge from the alternator (via the smart solenoid). It shouldn't receive any charge from the dc/dc charger as the dc/ dc charger is only charging the c'van batteries (and then only when the engine is running).

The purpose of the dc/dc charger (in my case) is to ensure full charging of the c'van batteries not the aux battery. As I have the redundant no. 9 pin already in the current system (and it has the ignition cut -out device in place). I was hoping to utilize my current system without to much extra wiring.

Does this make it any clearer?

Ian, this is getting complicated! Mainly I think because it's hard to describe in words what can so easily be described by a picture. I think the following is what we are talking about, but I could very easily be wrong! :

Image Could Not Be Found


With both the smart solenoid closed and the ignition switch closed there is a direct path from A down the right hand path to the INPUT side of the dc-dc charger AND a direct path down the left hand side to the OUTPUT side of the charger at B. The charger's input is directly connected to its output around the loop and it will either die or not function at all.

Have I interpretted your proposal correctly? The issue could be resolved like this but has the disadvantage that the aux cannot be diestly charged from the trailer charge system ( solar and mains).

Image Could Not Be Found

Cheers

John

Something went wrong there -

"The issue could be resolved like this but has the disadvantage that the aux cannot be diestly charged from the trailer charge system ( solar and mains)."

should have read "cannot be directly charged..." and the image that still refuses to load is simply as above, but with the diagonal link to pins 8,12 removed.

HTH

John

G'day again, again John & Val.

You are right about pictures vs words.

Hopefully the attached diagram can clarify the situation.

Image Could Not Be Found

Hi Ian,

The loop problem remains. The dc-dc charger operates by taking available input voltage and increasing it to meet the battery's requirements. It will get hot and bothered if it's output is connected directly to its input. With the ignition switch closed in your diagram there is a direct link around the loop from its input to its output.

An aside - I'm not familiar with the standard wiring arrangement in your vehicle, but I would expect the ignition switched pin 9 line to be fed by the cranking battery, not the aux battery.

The loop MUST be broken. This can be done by removing the long diagonal link to 8,12 thus leaving the aux battery independent. A further complication would remain if this link was removed - IF the pin 9 line is fed by the aux battery as you indicate, the aux battery will charge the other batteries through the dc-dc charger whenever the ignition key is in the accessories position without the engine running.

Ian, if you'd care to send me your email address by a Member message I'd be happy to continue this discussion privately.

Cheers

John