New to camping wondering about power systems

Hi John

I am in a similar situation to Geoff and are about to instal a dual battery system. In my instance I have a 100 series landcruiser td which has the duel start batteries.

Haven't decided whether to isolate the batteries or install a separate box in the back yet.

Have read your article and found it interesting, particularly comments regarding use of the dc to dc chargers.

What I am a little uncertain of is if using a charger is it possible to supply excess voltages which may damage the fridge?

I have just bought a gold Engel and the users guide advises not to use "quick chargers with excess voltage in performing their intended function" at the same time as the fridge. Maybe this is different type of charger than what you are talking about?

The other question is whether it is recommended there there be an easy way to disconnect the charger and charge directly from the alternator in the event the charger fails?

Thanks

Peter

Hi Peter,

Certainly some people do separate the two batteries in the 100 series, retaining one for the engine and vehicle electrics, and using the other as a deep cycle battery for household purposes. I hope someone who’s done this will comment here. My personal suspicion is that Toyota had good reasons to provide that second battery. My other thought is that it would be better if the battery powering the fridge was closer to the fridge. If in a trailer or van, then certainly I’d opt to have the battery there too.

Re dc-dc chargers. These chargers provide the charging regime required for the battery – initially a constant current stage during which the battery (and fridge) voltage rises to a preset value set by the user to suit the battery type. This is followed by a phase where the voltage remains fixed at that preset level and as the battery approaches fully charged, the charging current drops. Once the current has dropped to a low value the charger switches to a lower “float”voltage to maintain a trickle of current into the battery. The critical factor is that preset voltage, which will typically be set at 14.4 volts for most deep cycle batteries, a little less for gel types, and maybe up to 15V for calcium doped batteries. (These voltages are roughly what your alternator will supply to the starting battery/s.) Most dc-dc chargers also offer the facility to act as a simple power supply delivering up to their rated current at about 13.4 (usually) volts. All these voltages are within the normal range to be found in a vehicle.

The quick chargers that Engel refers to are probably the big mains powered ones that use higher voltages to force charge rapidly into the battery – best avoided in my opinion. The Engel site doesn’t give voltage specs for their fridges, so might be worth asking them just what they mean by “excess voltage”. I would not consider the voltages supplied by a dc-dc charger to be “excess”, but for the sake of your warranty best to ask Engel just what they mean. (FWIW, our Waeco is quite happy to run from the dc-dc charger.)

Is there an easy way of bypassing a dc-dc charger and charging directly from the alternator. Yes! On one trip our alternator failed and I turned the charger around 180 degrees (electrically that is) so as to charge the starting/vehicle battery from the house batteries and roof-mounted solar panels! (Our Troopy is petrol powered, so no electricity means no ignition.) How? Anderson plugs. The line to/from batteries and the line to/from alternator are both fitted with anderson plugs, so can be connected together to provide direct charging. The dc-dc charger is fitted with anderson plugs on input and output and inserted (electrically speaking) between the alternator and battery anderson plugs. (In speaking of connecting to the alternator here in fact the connection is via a circuit breaker and voltage sensitive relay to the vehicle battery, which in turn is connected to the alternator. )

Hope that makes sense!

Cheers

John

John

Thankyou very much for your comprehensive reply.

Have contacted Engel and they were very non committal on whether a smart charger could be used or not. Interestingly they do sell a battery box with inbuilt smart charger and when questioned about this advised of course there would be no problem with their own product.

What I am thinking of doing if I install the battery in the back of the wagon is to instal a conventional solenoid or vsr under the bonnet run appropriate cable to the rear to a anderson plug. I could then plug directly into a battery box or intalll a dc to dc charger in between if so desired.

I can even run the fridge of the existing rear power outlet whilst battery is charging to avoid any issues.

Peter

Hi Peter,

As you propose would make for a good flexible setup. Suggest run a good heavy twin cable (at least 8 SWG, 6SWG better, bigger) from the engine bay to the back of the vehicle for this purpose. If you can minimise losses in this way, you may find a dc-dc charger unnecessary.

Engel gear has a good reputation, but it's disappointing that they don't publish proper specs. The unwillingness of their people to comment on the suitability of smart chargers is unsatisfactory - implies ignorance, possibly due to the lack of published information by Engel - not the sort of support we expect from a reputable manufacturer.

Cheers

John

Thanks Terry

I have now purchased a CTEK D250S dc to dc charger which will regulate solar voltage.

My main worry is whether the smart charge functions ie various different pulse voltages and amps will affect the operation of the fridge.

Don't Waeco and Engel fridges work on 12 & 24 V without having to select which voltage you are using? If that is the case then they will handle more voltage than a 12 V system will supply.

My Engel definitely is 12 or 24 volt however does that mean it is happy to run on 14.5 volt?

I am thinking it should be ok as the alternator is pretty close to this anyway.

Guys,

Some of these fridges work off EITHER nominal 12V or nominal 24V, but not both and not in between. There is a big range of voltages found in 12V vehicles from up to 14.6 (sometimes higher depending on the type of battery) when charging, and down below 11V when pretty flat. (And double those for 24V systems.) Dunno about current fridges, but older ones were often straight 24V, with an internal voltage doubler to handle 12V vehicle systems. The awful radio interference they generate is due to that voltage doubler.

Peter, in direct response to your question "My Engel definitely is 12 or 24 volt however does that mean it is happy to run on 14.5 volt?"

The answer should be yes. 14.5V should be fine as it is within the normal range in a vehicle. 16,18,20 volts will NOT be fine though as the the beast won't be able to decide whether to regard it as excessive 12V or inadequate 24V.

Cheers

John

OOOPs! Finger and brain got out of synch!

"Some of these fridges work off EITHER nominal 12V or nominal 24V, but not both and not in between." WRONG - of course they'll work off both 12V and 24V, but obviously not at the same time!......

Cheers

John