Battery <span class="highlight">Solar</span> charging order Question for <span class="highlight">Solar</span> Gurus

The problem you will have is that your battery will never really be full on the camper and the charge curve will drop down to 1 amp for the last few hours and then the sun will go down before you can switch. You would be best to use those batteries as a bank and the panel can push its full 5A into the bank. The method I described at first would switch at 13.5V and then charge both batteries in parallel. This would utilise the full power that the panel can give you.

If you have a lot of money to spend on this project there are devices that can be used but I would not spend too much in this system.

Using a automatic isolator controlling a 30A double pole relay you could get the switching you are after. When the camper battery is below 12.5V it will charge on its own until 13.5V at which time the isolator will kick in and energise the relay which will divert the power to the car. When the camper battery drops below 12.5 the isolator will switch off and the relay will return the power to the camper battery.

It is a parallel system not switching. I have seen this unit.

The 50% / 50% priority setting splits available charge current equally between
two battery banks. This priority setting is ideal for systems with two equal-sized
battery banks that require simultaneous charging. If one battery bank reaches full
charge before the other, more charge current will be diverted to the lower stateof-
charge battery.
DIP Switch 3 OFF: 90% / 10% Priority (factory pre-set)
DIP Switch 3 ON: 50% / 50% Priority

Derek, looks like it is just you and me.

It simialrly says the following.


For the 90/10 setting is says "The 90% / 10% priority setting allows Battery #1 to receive 90% of available charging current, while Battery #2 receives 10% of charging current. This setting
is ideal for RV and boat systems where a “house” bank requires most of the available charge current and a separate engine starter battery requires only a “trickle charge” to remain topped-off. When Battery #1 reaches full charge, more charge current will be diverted to Battery #2 as needed."

Isn;t this kind of in parallep at 90/10 or 50/50 until one battery is full then it will go over to the other.
If I make the Trailer battery the 90% that sounds similar to what I want yeah?

Yes if you did not draw any power off battery #1 and then it started to push more current to battery #2 great. The problem is that this may not happen in a camping situation off a 100W panel. The system is good but I would not expect to get more then 1 amp going to the car unless the camper battery is full and you don't use it. (No radio, pump, fridge, lights). Even a few minutes using one of these items would decrease the chance that the car would get any more than 10% in any given day.

I do like the system and the remote head too but it is not ideal at the cost.

hmm I think that is a good point about the use as you go during the day.

Actually while looking at all of this I came across a MPPT charger. Several references to these talk about them being constant power instead of constant current. Ie instead of getting about 70W out of a 100W panel ( ie say 6A at 13.8V instead of 6A at 18V) you get about 8A at 13.8V or 9 at 11V. It achieves this by going DC - AC - DC internally and can generate more amps at the output than the input in the same way as a transformer can. They have 95 - 100% efficiency.

This is like getting 30% extra solar panel for not much more cost.

Do you have anything like that Derek?

Have you got a link ?

Take a look at these

They are called MPPT or Maximum Power Point Tracker regulators

Pretty good description of how they work and benefits

Morningstar MPPT

I have even seen some that can charge 24V systems from 12v.

They seem to be a DC - DC converter that always tracks the peak power output of a solar panel in any light condition, and has a 4 stage regulator built in.

i may have a 80 watt solar panel for sale if you in the sydney area - i have used it maybe 5 times - selling as i am upgrading to 160 watt system


Boc

Also here is a description from a different company called blue sky.

How Do Solar Boost™ Controllers Increase Charge Current?

Solar Boost controllers increase charge current by operating
the PV module in a manner that allows the module to produce
all the power it is capable of. A conventional charge controller
simply connects the module to the battery when the battery is
discharged. When the 75W module in this example is
connected directly to a battery charging at 12 volts its power
production is artificially limited to about 53 watts. This wastes
a whopping 22 watts or nearly 30% of the available power!
Patented MPPT technology used in Solar Boost controllers
operates in a very different fashion. The Solar Boost controller
continually calculates the module’s maximum power voltage,
in this case 17 volts. It then operates the module at its
maximum power voltage to extract maximum power. The
higher power extracted from the module is then provided to
the battery in the form of increased charge current. In
conditions where extra PV power is not available, Solar Boost
controllers will operate as a conventional controller with very
low voltage drop.

The actual charge current increase you will see varies
primarily with module temperature and battery voltage. In
comfortable temperatures, current increase typically varies
between 10 to 25%, with 30% or more easily achieved with a
discharged battery and cooler temperatures. What you can
be sure of is that Solar Boost charge controllers will deliver
the highest charge current possible for a given set of
operating conditions.

Waddya reckon?

Great but how will you switch between batteries.

I will give it some thought.

Dunno, and after your post 3 of 9 I am not sure that what I am trying to do makes sense. I have to apply some Vintage Port thinking juice to the problem.

Unless you switch the load.... but now it's getting too complicated. We don't know the load at this point.

Mainey
1) What Brand, type and size are each of the Auxiliary batteries your using ?
Wet cell Deep Cycle in the fourby Aux, ?? in the Van, probably similar for charging reasons

(2) Where will you have the Solar panel situated when working ?
(No, the answer's not "it's in the ###### sun")

Usually portable up tp 10m away, unregulated leads.

(3) Do you use a Solar regulator, (what brand & model is it) ?

That is the $64,000 question. I want one that splits the charge as described but now have MPPT as a must have feature.

(4) What current is being drawn from EACH Auxiliary battery ?

3way fridge mostly during travel plus lights and 2 way fridge, say 1- 4 A when stopped.

(5) are you prepared to get an extra Solar panel ?

Yep I dont have any now, and am thinking of 2 x 85W

(1) The problem you will have is the very slow charging time of a wetcell Deep Cycle battery by solar power in comparison to AGM batteries!
AGM DC batteries are recommend as they charge much faster and are the only battery type recommended for Solar charging.

(2) No problems here with the "lead" - BUT will require a Solar Regulator adjacent to the (actual) battery for best results.

(3) I would use a manual switch over system between the batteries, unfortunately as your batteries are placed a long distance apart, the effectiveness is limited to the closest battery to the Solar Regulator.

(4) Refrigeration would probably draw ~12ah to 15ah (Amp Hour) when the 3 way fridge is not running on gas or your travelling, so that has to be replaced in a 'day'
The two x 85ah Solar panels combined will give ~11 or ~12 Amps max for only the "peak" day light hours.

(5) Get a quality brand solar panel that gives good max rated power and one that will also work in low light conditions, this gives longer charging times per day, therefore gives more amps per 'day' than elcheapo solar panels will supply to the batteries.

Mainey . . .