48V charging via ST generator and solar charge controller (no ST mod)

[bschwartz]

Could these $99 48v power supplies be directly hooked up to a 48v grid tie inverter such as an outback, xantrex etc.?

[BruceM]

When I read some specs on MPPT solar charge controllers, I believe I read something about boosting panel voltage on cloudy days...if they have a boost converter, then you might be in luck for 48V.

[mobile_bob]

Bruce:

you may be right, i don't know for sure because i haven't followed the technology for a couple years

generally speaking though an mppt is best used with a higher voltage panel set and in buck mode,
when the cloud cover is such that the voltage drops to below the charge level there generally is not much power
available to cover the losses of conversion of a boost converter.

but they may not always be the case?

bob g

[BruceM]

There is a switching DC_DC design which can do both buck and boost, and I think that's what the newer MPPT units are doing.  There is no penalty for boosting vs bucking with that topology.  I just can't remember which unit did the boost conversion...

[Geno]

It doesn't look like the Flexmax or MX series does any boosting.

From the Flexmax manual

Nominal Battery Voltage Nominal Array Voltage (recommended)
12V 24V (or higher)*
24V 36V (or higher)*
36V 48V (or higher)*
48V 60 V (or higher)*
60V 60V (low temp is less than 5°F) or
72V (low temp is greater than 5°

* When sizing an array to charge controller with a distance of 70 feet or greater, OutBack recommends the nominal array voltage be slightly higher than the recommended nominal array voltage. Example: A 36VDC nominal array recharging a 12V nominal battery with an array to charge controller distance of about 70 feet or greater. Sizing the nominal array voltage higher than the nominal battery voltage ensures that the Maximum Power Point is always above the battery voltage. The Maximum Power Point will  decrease as the panels warm up, thus lowering the output of the array. The Charge Controller Charge Controller will not be able to boost the output if the Maximum Power Point of the array is at or lower than the battery voltage.

The MX60 is a buck type converter and cannot boost the output current when the PV array peak power point voltage is at or below the battery voltage as may happen on hot days in 24 VDC PV and a 24 VDC battery system or a 48 VDC PV and a 48 VDC battery system.

FLEXmax 80
The Charge Controller is a buck type converter with the following properties:
•80 amp DC output current limit (default setting)
•Listed to operate continuously at 80 amps (40°C/104° F)
With an 80 amp Charge Controller output current limit and PV array output higher than 80 amps offers little, if any, current boosting or Maximum Power Point Tracking advantage; in effect, any excess power beyond 80 amps is lost.


Thanks, Geno

[yellowhead]

Just to ask again (cos it probably got lost in my original post). Does anyone have any idea how a switch mode power supply like this will behave if I feed it 40Hz AC? I'm hoping to spin my head and engine at lower rpm while charging batteries ...

Sounds like the IOTAs might go down to DC but the specs show the same AC range (47-63 Hz)?

Simon.

[BruceM]

Thank you,  Geno.  Looks like it's buck or nothing.  My memory/imagination is wrong again.
Dandy for a 24V system, I guess.

Yellowhead-  I wouldn't go below 50Hz myself unless someone gave me some free Iotas to experiment with/smoke for fun.  Many switchers will do 120V 50/60Hz or 150-180 VDC input, but much below 50Hz the input storage caps aren't going to be big enough in most designs.

[yellowhead]

Thank you,  Geno.  Looks like it's buck or nothing.  My memory/imagination is wrong again.
Dandy for a 24V system, I guess.

I thought I'd seen a charge controller that did buck/boost as well. I think this was it (although its still not available):

The MidNite Solar Classic MPPT controller is destined to be the type of product that will truly change our industry. With a very aggressive list of features, the Classic from MidNite Solar is once again raising the bar in performance. The Classic has three separate modes (recipes) to choose from: Solar, Wind & Hydro. Each mode has key settings making setup a snap. Custom changes are also easy with the easy to navigate menu structure. The Classic also widens the battery bank size by allowing 12, 24, 26, 48, 60 & 72 Volt Nominal Battery Bank sizes. With maximum output at 60A, the controller keeps cool with an oversized variable speed ball-bearing fan. The design of the cooling fins on the chassis prevents the fan from running most of time, but the fan is easy to change if the controller lives in extremely harsh environments.

An industry first: Boost Mode. All other MPPT controllers on the market have Buck Mode, meaning they down-convert the higher array voltage to match the lower battery voltage. The Classic has Boost Mode allowing it to charge a 48Vdc Battery Bank from only a 24 volt source, for example. The Classic can Boost up to 60A of input voltage converting it to charge a higher voltage battery bank. Another first is the ability to parallel the inputs and outputs of multiple controllers allowing them to act as one larger controller. The Express-Bus communication network allows the Classic to synchronize with each and the MidNite Solar Equinox Communication Controller.

[yellowhead]

Yellowhead-  I wouldn't go below 50Hz myself unless someone gave me some free Iotas to experiment with/smoke for fun.  Many switchers will do 120V 50/60Hz or 150-180 VDC input, but much below 50Hz the input storage caps aren't going to be big enough in most designs.

Thanks for the warning Bruce. I wouldn't try it on an IOTA  I might push the limit on one of those $99 power supplies though to see what happens. I need to go and review SMPS theory a bit to understand why the input caps are the limiting factor. 47Hz would be 1400rpm on my set (more or less) which might work out just fine ...

[BruceM]

Yellowhead,  Thanks for posting the Midnight Solar info; I guess that's where I saw the boost converting MPPT mentioned.

One possible snag on Midnight's future product is that the combined buck/boost converter designs I've seen aren't quite as efficient as a straight buck (down) converter, which is the highest efficiency (and simplest) topology for DC-DC converters.

I don't think you'd have trouble at 47Hz. 

If a schematic was available, the output voltage of the cheap 48V switcher might be raised. 

[Halfcrazy]

Hey guys I am a Beta tester for Midnite solar's Classic I have 3 running here. I can assure you they are as efficient as anything else out there while operating in buck mode. They have some great features and more to come the first great feature is the ability to just upload software to them vie usb or ethernet. They assure me they sill be as efficient in boost mode but we have yet to get that far in testing. They have 24 units going out in a week and then they will build a production run shortly after that. I believe the first of may they will be available.

[mike90045]

Switcher on DC  - it's not the caps - it's the AC input rectifier bridge, instead of 4 diodes timesharing the AC input, it's only 2 on DC, and if they are near their design limit - poof!

[BruceM]

I was not referring to the caps regarding 40Hz operation, not DC.  Actually, all bets are off on this unit under spec'd frequency range  as it's power factor correcting. 

Unless you're ready for smoke, I wouldn't try operating a switching supply on DC that isn't rated for DC input.  There are a variety of things in the control circuitry which might be relying on an AC source.

[mike90045]

I did not know the iota's were PFC'd.  I sure missed that one.

[BruceM]

I was referring to the 3000 watt, 48V power supply on sale surplus for $99 when I mentioned power factor correction.  It's on the first page of the specs with link posted above.

I don't know anything about the IOTA chargers.