AC to DC battery charger questions

Re: AC to DC battery charger questions

Basically, that is my guess doing the math... If others have real world experience (what's that?)--I will differ to there experience.

Regarding the math... Basically, assuming PF=1:

• Generator Watts * eff of charger * 1/battery charging volt = "available amps at battery"

If you assume PF=0.6 ... Then you assume that only 60% of the amps*volts is converted into useful power (DC amps*volts) at the battery (maximum generator AC current but inefficiently used at battery charger because of "poor" power factor). So, this limits the maximum size of the charger.

-Bill

Re: AC to DC battery charger questions/add "gasoline" statement

Regarding optimum genset fuel usage... Very roughly, most generators are most fuel efficient from 50% to 100%+ of rated load. What happens below 50% of rated electrical load, the generators typically use ~50% fuel flow...

The Honda eu2000i (and some other inverter/generators) because the motor can slow way down at low power output (internal inverter in "generator" gives 120 VAC at 60Hz even if the motor is running slower). So, for the eu2000i, even running at 25% of rated load is still pretty fuel efficient.

Another issue is that diesel gensets really run best at 50-60%+ of rated load for best mechanical life (other thread).

So, the previous equations give you ideal load calculations (for chargers, pumps, etc.) on your genset.

Battery wise, the ideal charging current runs from 5% - 13% or even 30% of the 20 Hour Amp*Hour capacity of the battery bank (these are rules of thumbs--always check with the mfg. data sheet for actual numbers).

So, the optimum maximum size for a random battery charger is 51 amps (12 volts) on a Honda eu2000i (not PF corrected). That would give you a range of battery AH capacity of:

• 51 amps * 1/0.05 = 1,020 Amp*Hours (12 volt battery bank)
• 51 amps * 1/0.30 =170 Amp*Hours (12 volt bank)

The minimum "optimum" battery bank would be:

• 21 amps * 1/0.05 = 420 Amp*Hours (12 volt battery bank)
• 21 amps * 1/0.30 =70 Amp*Hours (12 volt bank)

So, ideally your battery bank for 3 days no sun and 50% maximum discharge times your daily load (6x daily load AH or Watt*Hours),--you would then look at the charger size to fit that range... And then look at the genset size to efficiently support the chosen charger.

One thing to remember is that batteries will take maximum charging current up to ~80-90% State of Charge (Bulk charging). The Charger's current (and power usage) will drop as the state of charge continues to increase (Absorb charging).

The aborb will continue down to ~2% of maximum charge rate, at which time a charge controller would switch to float charging.

The absorb, as the current drops, will pull less watts from the generator and may drop you into the fuel inefficient range (below 50% or 25% fuel use--depending on brand/model)... At that point, you will either let the solar panels finish the charging, or you may choose to stop the genset and call 90% "full" as good enough (and it really is except when you want to try equalization which, typically is done once a month more or less, and done at ~5% * AH rating of the battery bank -- and you will know is fuel inefficient (but only done on the genset rarely).

Note, a 1,600 watt genset can support a pretty large battery bank (even more if Power Factor Corrected charger is used).

One of may rants is to really choose the best generator size/brand/model to support your needs. That 15kW diesel looks really nice (10-30,000 hours between overalls)--but if you are only using a 1 kW most of the time--you are just pouring expensive fuel down its injectors for little return.

Placing a Kill-a-Watt meter (or other Watt*Hour Meter) on the output of your genset and keeping track of fuel used (gallons, pounds, cuft, gasoline, diesel, propane, natural gas) will let you calculate the kWhrs per gallon usage...

From what I have seen, a smallish portable genset will give you roughly 5-6kWhrs per gallon of fuel [that is per gallon of gasoline--other fuels/gensets will be different].

Take a large genset with 50% break point, and run it at 25% load, all of a sudden, you are getting ~2.5kWhr / gallon of fuel--and spending 2x in fuel costs for the priveldge.

I hope this makes sense (at least it made sense in my head while typing it :roll:).

-Bill

Re: AC to DC battery charger questions

notsobright wrote: »

what about using a AC to DC charger that puts out more amps than my solar charge controller is rated at, is that a problem? does the solar charge need to be off when charging with an AC to DC charger?

You can place each charger (and breaker/fuse) to the main battery bus (short, heavy gauge wire, low voltage drop). You will have some interaction (one controller may go into float while the other is still in Absorb)--but those will not cause issues.

The one major issue is if you have a big 30% rated AC charger and a 13% solar charger and flooded cell batteries--you could overheat them if both chargers were on maximum at the same time (full sun, equalize, etc.).

Check your battery's charging specification and don't pump too much current in.

Because you are using a generator--you will not overcharge (say AC charger does not have float mode)--because you will only charge until full (or even 90% full), then shut the genset down... You will NOT have have weeks and months of AC charger holding the batteries at 14.6 volts with no cycling vs having the charger plugged into a utility power outlet). If you do take the batteries "home" for a few months... Just charging them every month or two with a single state/two stage charger is just fine.

I dont understand Power Factor Corrector/correction. seems to be an optional gizmo on some chargers but what is it doing exactly?

Basically, the old battery charger have a diode (full wave rectifier) charging the battery bank... And this causes zero current flow just until the AC sine wave is very near the peak voltage--then there is a short surge of current into the battery, then nothing until the next peak. The current wave form sort of looks like this:

[FONT=Fixedsys]      /\
     /  \ 
----/    \---------\    /------
                    \  /
                     \/[/FONT]

This "non-linear" current wave form causes all sorts of issues. The basic one is this... One of the formulas for power is P=I^2*R (I squared times R or current squared times resistance). This is the formula used to calculate resistance heating. Notice that when the current doubles, the amount of heat goes up 2^2 (two squared) or 4x... That current spike is narrow but very high... So it cause heating in the wiring (and more losses in transformers and generators too).

That is a battery charger with a poor Power Factor (uncorrected Power Factor).

A power factor corrected battery charger basically has the current following the voltage wave form (sine waves in phase). This is the most efficient method to transfer AC power.

You can represent Power Factor as a decimal number... Basically PF=1.0 is a perfect voltage/sine wave form that transfers 100% of the energy.

PF=0.5 means that only 50% of the AC current that is going through the wires is transferring energy. The other 50% of the AC current is doing no useful work--but heating wires and transformers.

PF that is 0.95-1.0 is pretty much perfect energy transfer. PF=0.6 and below is pretty bad. Basically the wires, tranformers, and generators have to be 1/PF=1/0.6=1.67 time larger to charge the battery as a PF=1 battery charger would have to be.

Note, the motor will still use (roughly) the same amount of fuel--there is no extra work being done (other than the bit of extra heat wasted in the wiring and generator windings).

Bad PF limits you to using smaller battery chargers for a given generator size. Good PF allows you to use the maximum available power from your genset (or inverter, etc.).

the Iotas should come with a built-in on/off switch and the jumper wire for reducing output is pretty slack and they dont look too portable either. I havnt ruled them out though.

I am not quite sure I understand your question... Iota is a very solid and reliable charge controller (but probably not PF corrected). I don't think they have an AC power switch.

But I have no experience with Iota--so I will leave it to others who can answer those questions better.

-Bill

Re: AC to DC battery charger questions

The batteries should reduce their amperage draw pretty quickly as the 14.2 volts is not that high (heck, my car alternator is rated at 70-100 amps or so at ~14.2 volts).

I believe the current limits are really more based on pumping the current in at 45 amps no matter the voltage (current limit based charging)... If you find the current is too high (I don't think you will--but I do not now for sure), you could always cut back to 13.6 on the bigger inverter. A better voltage to "float" a full bank at anyway (AGM or Flooded Cell).

-Bill

Re: AC to DC battery charger questions

From here for the DLS 45:

[FONT=Arial,Helvetica]The DLS-45 Power Converter/Battery Charger from IOTA Engineering converts nominal 108-132 AC voltage to 13.4 DC voltage for both DC load operation and 12V battery charging.

As a power supply, the unit's tightly controlled regulation allows the user to operate a nominal 12VDC load up to 45 amps.

As a battery charger, the unit will maintain the battery, delivering its full-rated current when the battery capacity falls sufficiently low. The voltage is set to deliver its maximum current for the necessary period of time to minimize undue stress to the battery caused by heating of its cells. This helps to ensure the longest possible life of the battery. Over time, as the battery nears its full capacity, the DLS-45 will automatically drop the current, providing a float-charge to the battery to prevent self-discharge of the cells. [/FONT]

From the manual (PDF):

TWO-STEP VOLTAGE JACK
The two-step voltage jack allows switching from a long-term float voltage of 13.6vdc up to 14.2vdc. When the included dual voltage plug is inserted in the jack*, the voltage rises to 14.2vdc for occasional fast charging. When the plug is removed, the voltage drops to 13.6vdc to reduce battery water loss.

WARNING: To avoid battery damage, remove the Dual Voltage Plug when quick-charging is complete. NOTE: If the unit is equipped with an internal IQ4 smart charger, two-step charging is not needed and the Dual Voltage Jack is disabled.

The IQ-4 Module:

[FONT=Arial,Helvetica]Take your DLS Battery Charger to the next level...

The IQ Smart Controller offers automatic charging control for DLS Battery Chargers, providing longer and safer use of your system's battery. The IQ Smart Controller is compatible with any DLS Battery Charger model and is covered under our standard Two-Year Warranty.

[/FONT][FONT=Arial,Helvetica]The IQ Controller allows the DLS Charger to operate as an automatic 3-stage "smart charger." This gives the customer the benefit of Bulk, Absorption, and Float stage charging, increasing the charging capacity of the DLS charger and decreasing charge times, insuring proper and safe battery charging and minimizing over-charging. This "smart" technology monitors the battery at all times. If the DLS voltage remains in the long term stage for more than seven days, the IQ will automatically deliver a boost charge for a predetermined time, then automatically return to the normal float stage.[/FONT]

IQ-4 voltages (only 12 volt listed):

PREDETERMINED VARIABLES FOR OPERATION
Battery Voltage 12V:
[FONT=Fixedsys]Bulk  Absorption Float Low Trig High Trig Over Voltage 
14.8V    14.2V   13.6V  12.8V     14.6     15.2[/FONT]

• So, Option 1 would be standard DLS with no IQ-4 module.

You put the plug in and it charges at 14.2 volts--if battery is below 14.2 volts, will hold 45 amps until battery reaches 42 volts. Once battery is at 14.2 volts, current will ramp down to zero amps (if needed) to maintain 14.2 volts

You come by a little later and pull the plug (or wire in a switch) to put on 13.6 volt float. Controller will output 0-45 amps to maintain 13.6 volts.

• Option 2 is DLS with IQ-4 module. (from the IQ-4 Manual):

OPERATION OF THE IQ4 IN THE 3-STATE MODE

BULK STAGE - During this state, the charger will operate either at Full Current output or Constant Voltage output depending on the discharged state of the battery. A discharged battery will dictate the voltage and force the charger into constant-current operation. As the battery charges, the charger transitions to a constant-voltage operation. This BULK STAGE will continue for either 225 minutes or until the battery voltage reaches the “High Trigger” value (whichever occurs frst). At this point, the BULK STAGE will operate for another 15 minutes before switching to the ABSORPTION STAGE.

ABSORPTION STAGE - This state is limited to 480 minutes (8 hours) during which the charger will operate either at Full Current output or Constant Voltage output depending on the discharged state of the battery. During Full Current output, the charger is providing its full current rating and will slowly increase the battery voltage to the “Absorption Stage” voltage. At the end of the 480 minutes, the charger will revert to the FLOAT STAGE.

FLOAT STAGE - This charge state holds the batteries at Constant Voltage for a period not longer than seven days. During this state, the charger not only foats the batteries, but it can also provide load current up its maximum rating for other loads without depleting the battery capacity. The FLOAT STAGE will end when either the battery voltage drops below the “Low Trig-ger” point or at the end of seven days when the IQ4 initiates an equalization stage to remove sulfate layers from the battery plates. In either situation, the unit exits the FLOAT STAGE and enters the BULK STAGE.

And Equalize:

If the battery has remained in the Float State for seven days, the IQ4 automatically provides an equalization charge to dissolve any sulfate layer on the battery’s plates and to avoid stratification.

The "Equalization Charge" is the worrisome part for me regarding AGM/Sealed batteries...

Nowhere is the EQ Voltage listed. And nowhere is the EQ time/algorithm listed.

If you are OK with manual operation of the voltage plug--the two voltages 14.2v/13.6v for Bulk/Absorb and for Float should be fine with AGM batteries (assuming you turn off the 14.2 volt charging setting at the end of a charge cycle.

The IQ-4 is not really clear enough for what it does with EQ mode every 7 days... And the 14.8 volt Bulk / 14.6 volt high trigger seems to be a bit hot for an AGM battery.

On their website--I could find nothing regarding AGM's and proper operation with their chargers. I would either ask Iota more details on the IQ-4 and any issues with AGM batteries and/or just go with the manual mode. 14.2 volts should not be a problem for AGM until they are fully charged and you are ready to manually switch to float.

-Bill

Re: AC to DC battery charger questions

Also, there are different ways of "regulating" voltage/current/etc...

An "analog way"--standard "3-Terminal Regulators" they have a transistor that turns on a bit more or off a bit less to balance the voltage/current output. Any "excess energy" is lost as heat. Think of a water faucet--turn the faucet more on or more off to regulate the stream out the hose... Very inefficient. But very simple and rugged.

Then there is the PWM switching regulator--Pulse Width Modulation. Switch on 100% current/voltage output. Switch off 0% output. Use a capacitor/battery to even out the voltage/current for use down stream. Very "noisy" output. Not very efficient, but the regulator (switch) does not get hot. Cheap and simple. Think of a faucet that is either full on or full off.. Nothing in between.

The typical "switching regulator" -- has energy storage elements (inductors and capacitors) to store the energy to supply the needed voltage/current. Can be pretty quiet and stable. More complex but very efficient (80-95% efficient). Because of the cycling nature of the "switches" -- can use small/high frequency transformers for electrical isolation--and/or use inductors to step up or step down voltage/current efficiently.

For one example--a RAM pump... Take a long length of pipe from a small dam. Turn on the outlet valve and let the water "get up to speed" in the pipe. Now quickly shut the outlet valve. The momentum of the water wants to continue forward--but the outlet is shut... Have a second check valve to a higher water tank/storage area. The momentum of the water will carry some of the water up the pipe and into the storage tank. Once momentum is used up... Open the outlet valve again and get the water in the long pipe from the low dam flowing again... That is using the stored energy from motion to pump water up hill. Sort of how a "boost mode" type switching power supply works.

-Bill "water analogies R us" B.