Mains/Batt to Batt/Solar charging

[nickburt]

Been working on a friends overland Daf 4x4 this bank holiday weekend.
The Daf is 24v, the main vehicle battery is a bank of 2 x 24v.
I've had to strip out a lot of wiring due to poor design and installation causing a few problems, but now getting close to rebuilding.

The battery to battery charger is a 24v to 12v unit, which is fine. It has remote control capability. When the remote is triggered (currently from the alternator), the charger switches on. Which is fine, in it's own right, but, as per the rough drawing of mine above, he want's mains and solar charging capability.

The connection of battery to battery charging and solar is fine - the MPPT controller will take care of how the solar interacts with the other charging methods, but my concern is if the mains and batt to batt chargers are both on (i.e. shore power connected and the engine running) how they will interact with each other (again, assuming no change over switch). I think there's a possibilty of one back feeding the other and doing some damage.

So, what I'm looking for, is an intelligent system that will cope with all 3 possible methods of charging. At the moment, I'm thinking a change over relay to swap over between mains charger and batt to batt charger. When energised by the batt to batt charger remote control signal (alternator output), the batt to batt charger is used, if the engine isn't running, the mains charger is connected and the batt to batt charger disconnected.

This would leave the MPPT controller to decide how the solar and "other" charge supply interact.

Not sure that all makes sense, but see below.

 

[Hillbilly Heaven]

why not an inverter/charger and replace the battery charger and the 240 vac c/o switch?

 

[nickburt]

Hmm, a possibility. Just working with what's there at the moment. If I can come up with a more efficient system, I'm sure he'll spend the money.

 

[john61ct]

No need to worry about disparate charge sources charging concurrently in parallel to the same bank.

Is this an electric propulsion setup or just Starter + House storage?

Which is 24V? What is the native alternator voltage?

Does the b2b charger convert 24 to 12 or v/v?

What is currently the main source of charging besides alternator(s)?

 

[nickburt]

@john61ct Many thanks for your reply.

No need to worry about disparate charge sources charging concurrently in parallel to the same bank.

Hmm, not sure, but I guess the battery will smooth any difference. Just don't like the idea of a back feed to the charger with the lower voltage.

Is this an electric propulsion setup or just Starter + House storage?

24v starting/main battery + 12v house/auxiliary batteries.

Which is 24V? What is the native alternator voltage?

The original vehicle is 24v, so all native equipment, including the alternator is 24v.

Does the b2b charger convert 24 to 12 or v/v?

Yes, the B2B charger is 24v input, 12v output.

What is currently the main source of charging besides alternator(s)?

As well as the alternator, there is a mains powered 12v charger. This was powered from the mains shore supply or an inverter. Inverter used to power the mains charger not shown in the above diagram because this has all been disconnected due to the poor way it was installed and I don't intend to reconnect it that way - hence my diagram above.

For now, I'd like to keep with making use of the equipment he has (if only to try keeping the cost down for him), before resorting to spending on new gear.

 

[nickburt]

The vehicle is an ex MOD DAF 4x4 10,800kg flatbed.
The box body is a demountable comms body which has been converted for living.
Mixture of 12vdc and 240Vac equipment (water system, 3 way fridge, LED lights, TV, shower and toilet) in the comms body and the main vehicle retains it's original 24vdc systems, with the exception of a 24 to 12vdc dropper in the cab for the CB and reversing cameras.

 

[luthj]

The battery is both a consumer and source of current. Basically every charger is designed to avoid "back feeding". The circuits used simply don't consume power in that manner. Having multiple sources is fine. Whichever has the highest voltage will provide current first, and down the list until the batteries start supplying any overrun. It is the same in the charge regime, except the battery becomes a consumer instead of source.

There is no real need for an coordinated system unless you need to coordinate switching to float (based on return current to the batteries). Generally it is acceptable to have the charges set as similarly as possible (voltage setpoints). Chargers with timer-only based absorb cycles may need adjusted depending on usage. As having a solar charger complete a full absorb cycle, and then having a mains charger do the same can put unneeded stress on a fully charged battery (generally not an issue with flooded/non-sealed). If the chargers use algorithms (voltage rate rise) or current levels (shunt measurements) this is much less of a concern.

 

[john61ct]

Yes, all sounds just fine.

Of course each charge source should be within the batt spec'd profile, and wiring needs to be sized for combined max currents.

As you move forward, get charge sources that allow user adjustments to setpoints, so the algorithms are similar.

 

[DiploStrat]

FWIW, I have a similar setup, 24v alternator and 12v camper battery bank. I use a REDARC BCDC 1240D and it works very well. Also provided a handy place to attach an extra solar panel as my primary controller was maxed out. https://redarcelectronics.com/products/dual_input_40a_in-vehicle_dc_battery_charger

 

[DLTooley]

Theoretically, no problem. My concerns are about having both a starter and house battery on the circuit. The particular methodology of the solar charger also matters - an egg timer based absorb phase could overcharge. Also, with more complex wiring there is more possibility of error. Fusing properly should eliminate those risks. The complete separation between 120v and 12v wiring is essential.

The higher end RV systems do this automatically, and also provide battery management and info.

 

[nickburt]

Thanks for the advice guys.
I'm sticking with the kit he has at the moment, and will rewire with correctly sized cabling and put a change over relay in to auto switch which charging source is to be used by using the trigger signal from the alternator.

 

[john61ct]

Completely unnecessary but unless it fails, no problem.

 

[luthj]

Completely unnecessary but unless it fails, no problem.

My thoughts as well. I would suggest avoiding unnecessary resistance in the charging runs. The relays you propose would qualify as unnecessary in my view.