Solar Charge Controller Question...

Art

Hi, and a late Happy New Year to All! ,
I'm wondering why the docs for every solar charge controller I've seen forbids
the input of any supply on it's solar panel input other than power derived from solar panels.

I've got a unit that claims the ability to hack 10 Amps input,
so what's the difference if I remove the panel, and connect a 4 amp battery charger to the same input to top up the battery ?
Cheers, Art.

john p

Re: Solar Charge Controller Question...

I'm wondering why the docs for every solar charge controller I've seen forbids
the input of any supply on it's solar panel input other than power derived from solar panels.

Not true they all dont.
I have a 30A 12v PWM solar charge controller that has connected to a 10a 15v switch mode power supply permanently for the last 14 months and it works as a charge regulator for the batteries perfectly.
It does seem that some solar charge controllers do short their own input to regulate the voltage.. not very good for the power supply.

BB.

Re: Solar Charge Controller Question...

It depends... You probably could put a 10 amp battery charger on the input of a PWM type charge controller... But the problems may be more than any positive results.

Battery Chargers typically are just rectified sine waves--no filtering, so you could end up with a 0 to 17 volt input to the charge controller--which could really confuse the controller.

Also, the battery charger itself may regulate the output voltage, so adding another device could cause problems (extra voltage drop, PWM confusing the AC battery charger, etc.).

You also cannot, for example put a 24 volt storage battery, PWM controller, and 12 volt battery together. A solar panel is really a current mode device--the solar panel limits maximum current flow so the PWM controllers don't have to limit current themselves. If you placed a 24 volt battery+pwm controller+12 volt battery together--the 24 volt battery would attempt to output 100's of amps through the PWM charge controller (which has no current control) and would pop the controller or the wiring.

Now, with MPPT type controllers, many probably can be connected between a 24 volt storage battery and a 12 volt storage battery. The MPPT controller is actually an energy converter (high voltage/low current to low voltage/high current). So--it can transform the energy from a voltage source (storage battery) into another storage battery. Doing this has been a suggest solution for a 24 volt to 12 volt converter before.

There are other issues, say trying to connect a wind turbine+solar panels together on one charge controller. The wind turbine would over speed with no load--so it is not a good combination (same with a water turbine).

The issues are many and depend on many variables--it is easier to say don't do it because nobody can plan/document every conceivable use of these charge controllers. If you try and undocumented connection setup--then it is your responsibility for whatever happens.

Instead of me guessing what it is you are trying to do (and confusing everyone here )--What is it that you are trying to do or what is the problem you are trying to solve?

-Bill

Art

Re: Solar Charge Controller Question...

It seems my question has been answered thanks.

What is it that you are trying to do or what is the problem you are trying to solve?

I have a battery box project discussed here:
http://forum.solar-electric.com/showthread.php?t=6670
and I wanted to use it's solar panel input to float charge the battery when the whole thing isn't in use (which will be most of the time).
I guess I'll have to wire another fused socket that leads directly to the battery, and
connect the mains powered charger to that.

BB.

Re: Solar Charge Controller Question...

A "Battery Tender" or equivalent brand of maintenance charger can work well.

Also, I use a cheap 1 amp battery charger and connect it with a 120 VAC lamp timer. I set it to run 1 hour a day (or whatever I need to make up self discharge loses) and it works well for me (use mostly on cars in storage). Keeps the batteries charged and prevents them from "boiling" dry in a month or three.

-Bill

Art

Re: Solar Charge Controller Question...

Rather than hook up another plug,
I just wired the lighter socket straight through a circuit breaker to the battery,
so I can charge through it, but the solar controller won't be able to turn off the
load if the battery level falls too low.

Then I wondered if you could charge the battery with the mains adapter connected
to the load output of the solar controller? Not that I'd do it when there's no mention of it in the manual.
Art.

BB.

Re: Solar Charge Controller Question...

You probably could... Might charge the battery to a lower voltage--and if the controller cut the power, your loads + maintenance charger would be on the same circuit--probably not a good idea (AC chargers can get up to 18+ volts peak when not connected to a battery--could damage the loads or even the charge controller).

In the end, the charge controllers are not good for LVD (Low voltage disconnects). Voltage is a difficult value to relate to battery charge while under load. Also, many LVD's are only 8 amp max current--and putting any larger loads/inverters on the output can pop the LVD circuit.

-Bill