Multiple Charging Sources to the Same Battery Bank

[s/v Jedi]

Bill, I read before that people are saying that these Iota chargers use PWM to charge a battery. After reading their website, I can only conclude that this is nonsense. The Iota chargers output a nice, clean, regulated DC. Also, they can be used as a power-supply without batteries connected. This means it does not output a PWM signal.

I think the confusion is that they are switch-mode devices. But that is something very different. What they do is take the incoming AC and rectify that into DC. Next, they convert it to a high frequency AC (like 20 kHz) and that is put into a transformer to bring it down to the desired voltage level, after which it is rectified and regulated again. The advantage is that at these high frequencies (as opposed to 50 or 60Hz), the transformers are much more efficient and can be very small (and cheap).

PWM is a pulse signal, like a square wave. The difference is that it can adjust the width of these pulses, changing the duty cycle that way. The only devices that put pulse signals on boat DC systems are the snake-oil battery-desulphators etc. Pulses do not belong on a DC power system.

ciao!
Nick.

[hellosailor]

Nick-
The gentlemen who spoke to me spoke off the record, as his company (like most of them) prefers to keep any competitive advantages they might have in terms of knowledge and research. His job is full time engineering & R&D, and you'd recognize the company name immediately, but if that says "anecdotal" to you, that's the way it can stay. No skin off my back.
" Those are now being replaced by MPPT so it's the museum for PWM in that arena."
I don't know how to say this, but apparently all MPPT controllers are PWM chargers! MPPT is just the intelligence controlling the charger. It can be a microprocessor using a table and look-up array, or actually computing values, or something simpler and cheaper, but in the end if you can open the box and find a ring transformer (usually a gray ceramic ring wound with heavy varnished copper wires) it is a PWM charger.
At least, that's my understanding of it. MPPTs don't "vary" the voltage or current, they send pulses of DC into that ring transformer, because only pulses (effectively, AC) can be transformed that way to vary the voltage/vs/current on the output.

And as Bill notes, PWM chargers can be very well shielded and tuned so that they produce negligible RFI, and that at frequencies which won't bother the user. (Some even have a tuning adjustment, to shift the frequencies if they are problematic.)

[s/v Jedi]

Bill,

Yes, you are correct, the MPPT are a more intelligent generation of controllers that still use PWM. They have to. Let me explain:

A AC powered charger can get all the power it needs from the AC. The manufacturers strongly advise that the charger you select has an output rating of between 10% and 20% of the total battery bank Ah capacity. This has to do with the acceptance rate of the batteries, how much charge current they will accept at a certain voltage. At the advised capacity, the charger can do it's job optimally, at voltage levels that are good for the battery and the fastest way to charge them at safe voltage levels.

But for a solar controller, it's different. It is fed power from the solar array and that is a limited source for any practical array size on a boat. As much as the controller would like to, it can't sustain a high enough voltage on an (partly) empty battery because the charge current that comes with that voltage is too much, there isn't enough power coming in from the solar array. This is where PWM comes in the picture. Because the controller can put a decent voltage and current on for a (very) short time, hence the pulses.

The big difference here is that the average charge current is much less from a solar controller, as compared to an AC powered battery charger. If a 120A battery charger would output a PWM signal at 50% duty cycle, it could pump out 240A current during those pulses. That is not so nice on a 600Ah battery bank. The batteries can't accept that much so the voltage rises too high, electrolyte starts gassing etc.

However, if the solar array were big enough to provide all the power needed for maximum level charging, PWM would not be needed and one could use a constant DC instead. This is why more and more chargers accept a high DC input voltage (like 160-400V DC) in addition to regular AC input... they can be fed from a big solar array.

ciao!
Nick.

[hellosailor]

" This is why more and more chargers accept a high DC input voltage (like 160-400V DC)...they can be fed from a big solar array."
I've never heard that one before. two MPPT manufacturers both told me that the reason they accept higher voltages is simply because that allows for lower losses in the transformer, and thinner cables from the panels, because the same set of panels connected for high voltage (as opposed to high amperage) will be able to use much cheaper thinner easier to run cables, since the voltage loss per foot is less significant when you're dealing with high voltage arrays.

Once you want a certain amount of power from the solar array, UNLESS you configure the array for high voltage instead of high amperage, the physical aspects of the cabling get quite expensive. Not to mention, thick and cumbersome.

[s/v Jedi]

Originally Posted by hellosailor

I've never heard that one before. two MPPT manufacturers both told me that the reason they accept higher voltages is simply because that allows for lower losses in the transformer[...]

Yes, you are correct about the reasons for a MPPT controller. But I wrote:

This is why more and more chargers accept a high DC input voltage (like 160-400V DC) in addition to regular AC input... they can be fed from a big solar array.

and the "in addition to regular AC input" means that I was talking about AC powered battery chargers, not solar controllers.

So, when solar arrays get so big that they can supply all the power needed for a "maximum power" battery charger (charge current 10-20% of total Ah capacity), the array can be used as a power source for a regular charger. Look at the spec-sheet for the Victron Phoenix charger: http://www.victronenergy.com/upload/...2%20-%20EN.pdf

It has an universal input of 90-265V, 50/60Hz. But, it can also take 90-400V DC instead of AC. You couldn't use MPPT controllers anymore because they don't have a high enough power rating (biggest I know is 80A output).

ciao!
Nick.

[hellosailor]

Victron does claim their Phoenix is doing things in a unique way, with "different" logic from convnetional charges. So, whether they are using pure DC or pulsed DC may be a moot point, all part of the larger issue of whether they really have invented a better mousetrap--or just another way of selling them.

Drop off a couple of chargers & battery banks & I'll be glad to test them out in competition. Oh, wait...that might produce objective quantified results, the kind so few of the industry players really want to see get printed. ;-)

Since Outback's "60 amp" MPPT controller is rated for 7500 watts....Bear in mind that 90% of the recreational sailboat market is under 28' in length and something like 5% is more than 40' OAL. Most of the boating market couldn't fit more solar panels on the boat, unless they tiled the deck with them. Jedi is probably in the last single percent for recreational boat ownership versus size, I think the battery chargers for systems in that capacity tend more towards commercial and shore systems than whatever drives most of theboating market. Different design goals, and designs.

[s/v Jedi]

Oh, I agree that there's not enough room for panels. But what happens when they improve the panel efficiency 5 times?! There's room for that as I think the efficiency with current technology is 16%.

Most rectifiers will pass DC (it's just a bunch of diodes). If the charger uses switch-mode the first thing they do with incoming AC is rectify it, so I think most switch-mode chargers can accept DC too. That Phoenix charger is not very unique because there are many chargers with adaptive algorithms. Also, output current is not very high, but they can be switched in parallel for more power.

Outback now has an 80A solar charge controller.

90% of boats under 28' in length? I don't believe that, that must be a local thing. Here in Panama more than 50% is over 40' and we are often in between 100'+ boats. Panama is probably different than other area's, but anywhere in the Caribbean the under 28' category is a small minority.

Not that it matters here, because there's never enough room for the solar panels, no matter the size of the boat.

ciao!
Nick.

[hellosailor]

"90% of boats under 28' in length? I don't believe that, that must be a local thing."
Indeed, local to the US. I would expect that to vary in other venues, and to be comparable among comparable economies, i.e. you've got to have a lot of rich folks to have bigger boats. VERY rich folks, before you get a harbor like some in the Med.

We also refer to anything 100+ feet long as a "ship" not a "boat", unless it is a submarine, which is by tradition always a "boat". At that point it may still be recreational--but the odds are there's a professional crew, so it is no longer "just" a recreational boat, but a crewed yacht.

In the last few years a number of announcements have been made about super-efficient solar cell breakthroughs, often accompanied by invitations for investors. But so far--no revolution on the shelves. Considering how long battery technology has been stuck at roughly the same place...as the saying goes, always a bridesmaid, never a bride.

" so I think most switch-mode chargers can accept DC too." In theory, perhaps. In practice, it would depend on what is done with the AC before it is made into DC, among other things. AC can be put through transformers, real DC can't. Whether you could just "insert" DC would depend on how the entire charger had been designed.

[s/v Jedi]

Well, we must still get to those places where 90% of the boats is under 28' in the US then. It's nothing like that in Florida.

But for solar power, we should like at cruisers that travel around because they are the ones using solar power. Day/weekend sailors based in a marina don't have the need for living on solar. And like I wrote, in the Caribbean, 90% is over 30' if not more. And this has nothing to do with money, because the cruisers out here often sell the house etc. to finance everything.

Ship/boat: Oh no, don't tell a Dutchmen how it is, we invented a "yacht" (Dutch word). A ship is for carrying cargo or passengers; a ship is never a yacht. A ship has a captain; a yacht, river barge and submarine have a skipper (another Dutch word).
So, you can have a 120' yacht. A boat is supposed to be able to be carried on deck/davits of a ship but the word is misused so often that some ships are called a boat too (ferries etc.)
Sloops, schooners, ketches, yawls are all boats or yachts, depending on their purpose, never ships. A ship had to have at least 3 masts during the sailing era. I know it would be convenient to have some like < 100' is boat and > 100' is ship but unfortunately that's not how it is. But things change... not so long ago I heard that yachts, boats and ships are now to be called "it" instead of "her" so more silliness is to be expected ;-)

In theory, perhaps. In practice, it would depend on what is done with the AC before it is made into DC, among other things. AC can be put through transformers, real DC can't.

Ah, but that's the thing: a switch mode charger doesn't put the incoming AC through a transformer. The first thing it does is rectify it. This is why they are small and light.

There must be more incentive before big leaps in solar technology are made. Real big solar installations make hot water or steam and are very efficient. The new battery technology came about because of the advance of small handheld gadgets and electric/hybrid cars etc.

Let's hope for better panels, that's all we can do.

ciao!
Nick.

[hellosailor]

Ah, switch mode supply, as the kind used in computers. I think that's technically still pulsed DC, not pure DC, it is just that the capacitor bank is smoothing it back to a DC output. Great for powering electronics, but I can't see it being any advantage when charging a battery, which isn't as sensitive to the purity of waveform. (Or lack of it.)

[btrayfors]

Nick,

Just back from a short sailing trip.

PWM control technology is ubiquitous in modern switchmode power supply systems, for everything from small consumer electronics to large military systems. PWM devices are used to control the output of the SMPS units, providing a number of benefits including small size, lower cost, and more efficient power delivery.

This is not to say that the output current of SMPS units -- like the Iota -- is necessarily pulsed. I've never put a 'scope on my Iotas, but will try to do that this coming week and see if anything interesting can be discerned.

I agree with you about the "snake-oil" small pulsers (and, in fact, did an 18-month test of several of these devices).

However, larger scale pulse chargers such as investigated by Ford and others seem to have very good benefits for lead-acid storage batteries.

Bill

Originally Posted by s/v Jedi

Bill, I read before that people are saying that these Iota chargers use PWM to charge a battery. After reading their website, I can only conclude that this is nonsense. The Iota chargers output a nice, clean, regulated DC. Also, they can be used as a power-supply without batteries connected. This means it does not output a PWM signal.

I think the confusion is that they are switch-mode devices. But that is something very different. What they do is take the incoming AC and rectify that into DC. Next, they convert it to a high frequency AC (like 20 kHz) and that is put into a transformer to bring it down to the desired voltage level, after which it is rectified and regulated again. The advantage is that at these high frequencies (as opposed to 50 or 60Hz), the transformers are much more efficient and can be very small (and cheap).

PWM is a pulse signal, like a square wave. The difference is that it can adjust the width of these pulses, changing the duty cycle that way. The only devices that put pulse signals on boat DC systems are the snake-oil battery-desulphators etc. Pulses do not belong on a DC power system.

ciao!
Nick.

[s/v Jedi]

Yes, that kind of switch-mode ;-) This is what the Iota charger does too. But the output is fully regulated so pure DC.

cheers,
Nick.

[btrayfors]

Nick, et. al

I had a little time in the shop this morning to put a scope on the Iota and compare it with 5 other power supplies.

Procedure

1. Iota DLS-45 charger w/ext. IQ-4 smart regulator connected to bank of 2 fully charged Trojan T-105 batteries
2. GW Instek GDS-1102 digital storage oscilliscope (DSO) w/10X probe
3. Used AUTOSET to acquire and display signal on the Scope; used MEASURE to view stats
4. Repeated measurements numerous times to be sure of what I was seeing.
5. Performed same measurement (steps 2-4 above) on five other power supplies, viz
a. Daiwa PS-50TM
b. Mastech HY5020E
c. Astron VS-35M
d. Astron RS-35M
e. Daiwa RS-300

Results

1. Iota charger showed clear and unequivocal pulsing, with variations in amplitude, duration, rise times, duty cycle, etc. This seems consistent with some sort of PWM technology being used on -- or carried thru to -- the output of the charger.

2. The pulsing continued even when the IQ-4 was unplugged from the Iota DLS-45.

3. The pulsing diminished and stopped when the DLS-45 was unplugged from the AC mains.

4. None of the other five power supplies showed any pulsing. Output was very clean, except for the MASTECH HY5020E (a variable 20A supply capable of providing up to 50V DC), but even its output was pretty clean.

Conclusions

1. Extrapolating from this one test and one Iota model, there is no longer any question in my mind that the Iota chargers do in fact use some sort of pulsing in their output to the battery bank.

2.This conclusion validates what I have been told by two Iota engineers, i.e., that the charger does use PWM technology (duh...it's a switchable mode charger) AND that the pulsing is carried right to the batteries.

3. Four of the other five power supplies I had readily available for testing put out pretty pure DC. The fifth was not quite so pure, but definitely was not pulsing insofar as I could determine.

4. The (now I can say) fact that Iota chargers use some sort of pulsing technology validates what I have seen and reported on in the real world, i.e., that they seem to maintain battery capacity better over time than do even high-end smart pure-DC battery chargers.

Disclaimer: I am not an electrical engineer nor am I a power-supply designer. This is an extremely complex field in which many EEs spend their entire careers (Texas Instruments alone has over 300 application notes pertaining to PWM technologies in modern power supplies).

However, I have been an Extra Class Ham for many years and have played with radios and power supplies and chargers and boats for over 40 years. For the past several years I have been a working marine electrical and electronics professional, having installed DC and AC power systems -- as well as other electronics and communications systems -- on boats from 30' to 130'.

Although this might mean I know a thing or three, readers should use caution when interpreting my comments here and elsewhere.

Bill

[hellosailor]

Bill, does the difference in output (pure DC /vs/ pulsed) happen to correspond with whether the device was called a "power supply" versus a "charger" ?

I'd want pure DC from anything sold as a power supply, but not necessarily from a "charger". Case in point, the popular Honda gensets, which have an incredibly dirty "12v" output that even Honda says is intended for charging, and not power supply.

[s/v Jedi]

Bill,

Very interesting test! Do you remember the pulse amplitude from the Iota (how many mV above the battery DC)?

What I don't understand is the IQ-4 regulator. I've never seen external regulators connected to battery chargers?? I am obviously not familiar with Iota chargers ;-)

I recently had trouble with a Xantrex Freedom 30 inverter/charger. I think a diode in the charger part was blown (I blew a fuse between charger and batteries, which normally means the diode(s) are history) and my Danfoss compressors all stopped complaining about DC supply. I measured a 100 mV ripple on the DC (no scope so I don't know the wave form but it must have been a 60 or 120 Hz AC ripple). This means that a charger that outputs 100mV pulses superimposed to the battery DC voltage will probably harm or stop the inverter/control unit of Danfoss compressors.

I believe that high amperage power pulses from a charger can be good for charging batteries. But you would need to isolate the batteries from your 12V distribution wiring during charging, which is not something I want.

ciao!
Nick.