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But he did avoid actually answering the bit of the question about the 12v battery.



My latest post to the seller...



I know the device will work with a 36v 230 watt solar panel, but you didn't mention the 12 volt battery in your reply.

Please answer ALL of my question....

Can I use this device to charge a 12 volt battery with a 36v 230watt solar panel?

Don't waste your time:

Rated Voltage: 12V/24V
Max Load current: 20A
Input voltage range: 12V system ≤20V / 24V system ≤ 40V
Overcharge protection: 17V/34V
Full charge cut: 13.7V/27.4V
Low voltage cut: 10.5-11V/21-22V
Temperature compensation: -3mv/°C /cell
No load loss: ≤20mA
Max wire area: 4 mm2
Ambient temperature: --25°C——+55°C
Dimension: 193 x 110 x 48mm

Is that from the original manufacturers site?

It's written slightly differently than the two different versions I have.

Yay! Three different versions now

Goodness BW, just plug it all in, double check your connections, and slowly bring it into the sun, while you measure all the voltages to make sure you're not exceeding your specs.

A bit of sun won't blow it up :-)

The worst that can happen is that it will clamp your solar panel voltage to 18 volts. Not a big deal, as the solar panel was clamped to 0 volts when the manufacturer did a max current test.

Make sure that it's not trying to charge your battery past 14 volts and you should be fine. Then measure your solar panel voltage and confirm that it's around 28 volts. If it is, then everything's working perfectly :-)

ok

The seller finally admitted that their product didn't do what their ebay listing said it could. Paypal has offered to give me my money back.

Now I have to post "FRAUD WARNING! Product is not as described" in their ebay feedback every day until they correct their blurb.

And I also have to hock a lot more blog posts to raise the money to go with the decent quality solar charge controllers that everyone pointed to.

I hate it when adages like "You get what you pay for" come back and bite me.

The Steca PR series regulators (German) will handle up to 47 volts and have the LCD readout. I use them in the camper installs I do and for a PWM charger they are fantastic.

My advice would be to spend the money on a regulator with a LCD screen and use the load function to draw your power from. In a system like you are building it is important to be able to get accurate figures in regard to both solar production and appliance draw. The good regulators will allow you to do this and without it you are flying blind.


Go for a larger amp reg if possible so you can add more watts later if you need without having to re purchase another regulator. You can not buy another smaller reg for a second panel, all panels need to run through the one reg otherwise they will conflict with each other.

If I'm running it from a 36v panel, and charging a 12v battery, I think I need MPPT, otherwise lots of power is wasted isn't it?

Some argue yes some argue no. I have never tested a higher voltage panel on them but there are some on the camper trailer forum I frequent who are successfully running 36 volt panels through PWM regs. The MPPT on 12 and 24 volt systems will only kick in during the boost stage when the battery is depleted so there are plenty who argue that MPPT is not worth in on a balanced 12 volt system as it will only run boost for around an hour in the morning if the battery has been drawn down overnight.

Cheers,
Mike

That is only for very small non-adjustable regulators, for any quality charge controllers with adjustments it is no problem at all. I have 4kW of PV running 3 arrays through 3 independent good quality MPPT charge controllers, charging Lithium batteries. It works just fine, and one CC has a 200W Wind generator in parallel too. It is just a matter of setting the charging transition voltages properly.

If you have a panel that maxes out a small regulator and want more power, ie another panel of the same ratings- you can orient the panels to do that, and not overload your existing regulator. You will also better match your energy production to your load- with no big midday peak. One panel faces east- tilted up from horizontal by 60 degrees, and the other tilted up 60 degrees, facing west. The panels will now be facing 120 degrees apart, so at solar noon each will receive half the solar radiation, and a couple of hours after sunrise or before sunset, one panel will be face-on for full power, with the other receiving minimal radiation.
It works, I've done it, and written up the results here:
http://forums.energymatters.com.au/sola ... c5064.html (I'm forum moderator there)

Nice to know Gunagulla, thanks. I tend to only deal with smaller (100-300 watt) RV systems.

For those who don't know though, with the smaller non adjustable regs as most here are using for their 12 volt systems the reg reads the battery voltage and bases the charging stage based on that voltage. If you hook two regs up they read each others charging voltage as the battery voltage which generally causes them to drop into float/maintain mode as they think the battery is full.

Yes, lots of power is wasted during the Bulk stage of charging, it is equal to (Vmp -Vbatt) * A, not including losses within the charge controller.

ie for a 100W 37Vmp panel it is approximately (37-12) * 2.7 = 67W wasted.

PWM controller delivers about 32W
MPPT controller delivers 100W

Of course, that is only when the panel cells are at 25C and there is 1000W/m^2 of radiation. In Australia, panels generally run at much higher temps, unless you are in alpine regions with temps near zero when the sun is well up, so actual output from the panel will be less for most of the time. Cloud edge effect can increase a panel's output by at least 25% too, PWM controllers miss that entirely, MPPT make use of it, so long as it isn't more than the controller is rated for.

MPPT controllers are of benefit during all stages of charging if you have a load plus battery charging requirements equal to more than panel current * battery voltage.

Yes Burnsy- regulators should never be set up such as they are reading each others voltages! Also, each regulator must be running an independent panel/array.
If 2 small regulators are hooked up to a single battery (of sufficient capacity that the voltage doesn't fluctuate too wildly when charge is on or off), then they will sort of share the load- if their charging requirement is low, ie generally near the end of absorb stage, or during float with minimal loads, then they may cycle back and forth- one then the other will do most of the charging. This isn't really a problem, so long as the charging requirements are being met... but it is not really the ideal way to do the job.

The MPPT function is active at all times.
With a PWM the panel is at the battery voltage so his 230w panel will only deliver about 110watts. That might be enough to charge the battery over the day with no load, but not much else.


With MPPT it will deliver up to 230w. That's an extra 120watts that's available for the motor and or battery charge.
It also means that when he stops there will be almost 50% more charge going into the battery (in sunlight).

PWM only makes sense if you have a close battery-panel voltage match and the system will sit on float for most of the day. Camper trailer situation where you generally only have a load for a short period at meal times is a possible scenario.
Having a 36v panel on a PWM is just a waste of room on the trailer.

I don't agree with this in that a quality PWM reg that is capable of the higher voltage will still produce 230 watts on a 12 volt system.

In regard to MPPT on 12 volt, regulators will only use the MPPT function (where it finds and uses the maximum power available along the voltage watt curve) will only kick in during boost mode. The rest of the time the regulators use PWM. Therefore unless your battery is depleted and triggers the regulator to go into boost mode MPPT will not be in use.

If you have a 30 volt plus panel privateer I would love to get together and test it with a Steca PR regulator and possibly proove me wrong if you want. There are quite a few MPPT vs PWM videos on youtube that cover the MPPT during boost senario.

Burnsy- I can assure you that my Outback FM80s (and I think all other quality CCs) use MPPT in Bulk (probably what you refer to as boost), Absorb and Float stages. It also will use MPPT in Equalisation, although I dont use that mode for Lithium batteries.