Nice layout. A couple of questions about FATMAX:

1) What is you max PV input, the Voc?
2) That is a big inductor. What is the L? Is your switching frequency less that 30KHz?
3) What is the output voltage and current? Does FATMAX have a battery charge control algorithm?

Max PV input is 45Voc.
Switching frequency is not fixed. It varies with varying input current, input-output voltage ratio. However, it is typically 25Khz.
The inductor is 47uH.
The output voltage various with the load resistance.

Hi Tony B,

A few Fatmax questions.

1. Can I run two conventional '12v panels' in series with this unit? ie is the Voc sufficient.

2. Is it best to run panels in series or parallel with a Fatmax or any tracker for that matter?

3. Will it work fine in conjunction with a typical PWM regulator, say a PL20? Does the Fatmax get confused/ lose track once PWM regulation kicks in on the regulator?

4. Have you done A/B testing with the Fatmax retrofitted to an existing system? ie switch in the Fatmax - record current/volts , switch out the Fatmax record current/volts to load/battery etc. This will not only demonstrate the feasibility but also typical efficiency gains of retrofitting.

Wahroonga Farm wrote:Hi Tony B,

A few Fatmax questions.

1. Can I run two conventional '12v panels' in series with this unit? ie is the Voc sufficient.

2. Is it best to run panels in series or parallel with a Fatmax or any tracker for that matter?

3. Will it work fine in conjunction with a typical PWM regulator, say a PL20? Does the Fatmax get confused/ lose track once PWM regulation kicks in on the regulator?

4. Have you done A/B testing with the Fatmax retrofitted to an existing system? ie switch in the Fatmax - record current/volts , switch out the Fatmax record current/volts to load/battery etc. This will not only demonstrate the feasibility but also typical efficiency gains of retrofitting.

Sorry to jump in here but wouldn't it be better to mount the Fatmax near the batteries so there is less resistance loss through the wiring from the panels? If it was done this way a relay controlled by the PL20 could switch the panels from the Fatmax to the PL20 when boost voltage was reached so the PL20 took control of the absorption and float charging as peak panel output is nolonger needed once boost voltage is reached. If the output from the Fatmax is fed into the PL shunt the input will still be measured by the PL20 so all the normal functions will still work correctly.
Just a thought

T1 Terry

PS TonyB, If you want me to do a test and record of a Fatmax I would happy to do one in a real life situation and give you a qualifying solar input using a separate panel with short circuit amps measurement.

T1 Terry wrote:...If it was done this way a relay controlled by the PL20 could switch the panels from the Fatmax to the PL20 when boost voltage was reached so the PL20 took control of the absorption and float charging as peak panel output is nolonger needed once boost voltage is reached. If the output from the Fatmax is fed into the PL shunt the input will still be measured by the PL20 so all the normal functions will still work correctly.

Hi Terry,

Thanks, but that's getting way too complicated. If that is the case I've badly misunderstood this particular application.

I was looking for a cheap and cheerful MPPT upgrade/retrofit to typical a RV solar implementation.

I was responding at this statement regarding the rev 2 Fatmax, "Can be, used in conjunction with regular solar regulators" from here.

If you don't have a shunt kit fitted to the PL20 then what I suggested is not a straight forward fit up. However if you do have a shunt kit it's fairly simple wiring and a commonly available relay. I also have a Motorhome (well building one anyway) so I'm very interested in these units if their operation/cost is better than theMX80 outback controller.

T1 Terry

T1 Terry wrote:...so I'm very interested in these units if their operation/cost is better than theMX80 outback controller.

T1 Terry

Exactly where I'm coming from. I see you've been doing some test comparisons.

It'd be good to see a complete run down of MPPT tracker vs MPPT regulator (MX60/80), vs PWM regulator (PL20) etc.

I guess I was also thinking of retrofitting a bog std dumbed down PWM regulator ... rather than a smart PL20.

Ive been meaning to get this thread updated for a while now, but been to busy as its been solar car racing season.

Ok, where do i start...

The unit shown in this thread is the prototype unit.

The FATMAX unit for sale on solarmppt.com is a 150 watt unit. If you look closely, you will see there are differences in the PCB compared to the unit shown here. The unit on solarmppt.com is rated for 150watts and 30Voc. That is the rev 2 design. You may connect your panel whichever way you like, but don't exceed 30Voc with this model.

There is new unit in the works rated for higher power, and it will have output voltage limiting. Ill post some pictures up soon.
You will be able to run two conventional 12v panels in series or parallel with the new unit, as it has a very wide tracking range. With other trackers, you need to make sure your solar panels maximum power point lies withing the tracking range.

The FATMAX, all versions, are designed to work with conventional charge controllers, PWM controllers, regulators, and they can even drive motors directly for water pumping use. When used with normal charge controllers, if your batteries reach a full state, or the charger decreases the power draw from the FATMAX, the panel voltage will rise.

Guys ill post the test results in the near future. Typically, on a full sunny day, charging 12 volt batteries from a 12 volt 85 W panel, the gains are 5 - 10 watts. And even more for higher voltage panels and lower voltage batteries. Remember, a typical 12v solar panel has a mpp around 16-17 volts, and your batteries average voltage is around 13 volts.

Hi Tony,

Tks for the answers. It's good to be busy:)

So it appears that the panel MPPT is completely decoupled from the load output voltage which varies with the load resistance and can happily accommodate PWM loads?

Wahroonga Farm wrote:So it appears that the panel MPPT is completely decoupled from the load output voltage which varies with the load resistance and can happily accommodate PWM loads?

That is correct. Doesnt matter what the load resistance is, the panel will always be at its MPP.

Example:

We have an 80 watt panel with mpp at 16 volts, and Imp at 5 amps, and a 1 Ohm Load.
If we connect the 1 Ohm load, we would be only getting around 5.2 volts out of the panel at 5.2 amps due to Ohms law.... That is 27watts... because the panel cant deliver any more current..

However, if we used a MPPT, the panel would be at 16V @ 5A ~ 80watts. The MPPT will switch the output voltage down and current up to match the load. So if we connected our same 1 Ohm load, we would have 8.9 volts across our load at 8.9 amps, that is 80 watts. Ofcourse, the current and voltage will vary for different load conditions, but the panel will always be producing 80 watts, or Pmax.

I guess the emphasis is on a rapidly PWM switching load, rather than a static or slowly changing load.

Does the Fatmax exhibit output hysteresis when connected to a std PWM solar regulator, once the regulator has achieved the bulk charge set point and has entered PWM switching to regulate battery current (and voltage).

We may assume in this situation, that the panels optimum output exceeds the loads requirements, ... but maybe not, so MPPT may still be important.

Are you marketing/selling this device as of yet?

Hi,

I found this forum by a bit of Googling, as I've been trying to get an answer (for a few weeks now) to a question asked directly of solarmppt.com, but can't get any response, either from the message system on their site, or via direct email.

Does anyone know if they are still trading?

I hope they are, as I believe that the Fatmax will be pretty close to ideal for squeezing an extra bit of efficiency from the panels on my low power electric river cruiser. I just need confirmation that it'll be able to cope with driving my lithium battery charge management system before I place an order. Having confirmation that their still in business would be good, too!

Jeremy

Edited to add:

Since posting this last night, Anthony from Solar MPPT has been in touch and confirmed that the Fatmax will do what I want, so I've ordered one!

Hi,

If this topic is still current,
How did the FatMax go ? I am interested to know if it is a commercial unit.
I have developed a Solar Maximiser.

I think there is no way that the unit displayed can give > 95% efficiency because

1. There is not enough input capacitance.
2. The Inductor wire gauge is thin and will get warm.

But I may be completely wrong, also why are there 6 FETS ?, it is an interesting design.

Please forgive my criticism, I have had great trouble getting my design > 90%.
*Specs, 20Amp In / out (240Watt 12V, 500Watt 24V)

If your unit is > 95% then I am very impressed.

Hello,

The Fatmax has shown efficiencies greater than 96% when input voltage is 18volts and output voltage is 14.5volts @ 70watts, which is a typical working condition.

1.The input capacitance is not too small. The capacitors used are Low-ESR, and ripple is minimized because of the high switching frequency. 40-60KHz variable with load.

2. The inductor wire is not too small, its 1.27mm squared, and good for 12 amp continuous. A typical situation would be 5amp input, and 6 amp output, which the inductor can easily handle. Infact, there is more core loss in the inductor as opposed to copper loss.

There are actually 3 paralleled nFETs, driven with a very high slew rate to minimize switching losses, and very low Vf diode (the bottom three).

If you live near Sydney, i can show you a working design.

Maybe we can even share ideas?

Cheers.

Tony,

the design works well.

I have a 24V 175W panel connected to a 12V battery, with out the Fatmax I was only gettitng 5A from the panel but now with the MPPT I have seen over 10A.

I am now using a controller from Electus that ensures the battery does not overcharge by turning on a load to control the battery voltage.

Excellent unit.

Robert Im glad you like it. I'm going to design a new unit soon, it will have output voltage programmable via USB.
Might even incorporate some charging algorithms if i get time.

Anyways, i know your using a 175watt 24v panel on yours. You'll be seeing input to output voltage ratios of around 2.5:1, so the diodes are conducting for the majority of the time, and at full load, you could have around 7-8watts of heat dissipated in them. For a small PCB, that could lead to a bit of temperature rise.
Keep an eye on their temps.

Show us some pictures.

pictures, still a mess so no way.

I have a heatsink attached to the board taking away the heat from the diodes, but it is quite warm. The coil rating is just over 10 amps and it is pumping that out at max sun, measured over 100C on the coil.

Is that at full sun from 35Vin to 14Vout?

I have a larger ferrite coil rated at 15amp, 100uH, it will definitely run cooler with it.
I'm estimating around 60-70°C at 175Watts. The inductor on the PCB now is rated for 150 watts or 12A.

How is it going with the software?

Would u like to share more about FATMAX.I have sent you a PM.thx!