Question about battery charger selection with EU2000 generator.

Re: Question about battery charger selection with EU2000 generator.

I will take an engineering back of the envelope shot at the answer--somebody with more experience charging battery banks with one can give you more information.

SteveK wrote: »

I have a 450 ah 24V battery bank.
Typical DOD of 70% drawing ~1500Wh/day at 10C.

Just to be clear... State of Charge of 75% would be a battery with 75% of its charge still left in it.

Depth of Discharge of 75% would be a battery with 25% of its charge remaining...

I am assuming you are using 30% of your battery capacity every night? So, the first night is 70% state of charge (70% full?)?

Your battery has a capacity of:

• 450 AH * 24 volts = 10,800 WH
• 1,500 WH / 10,800 WH = 0.14 or 14% per day draw down
• 2 days * 14% = 28% DOD or 72% SOC remaining

And, we would like to limit the maximum draw down to 50% for long battery life (get recharged quickly back above ~75% to limit sulphation damage).

I would like to add the Iota for those 2 day without sun events instead of unplugging my chest freezer and coal stoker to allow full charging.

Assuming I am understanding you correctly--You can go 2-3 days very easily with "no sun" before needing to crank up the genset for some remedial recharging.

I would also desire the EU2000 to run at or near idle speed while charging the batts.
...
I am under the impression that operating these generators closer to low output increases their efficiency at the expense of run time (which I have plenty of at ~8-9 hours per tank)

Actually, the Honda euX000i family just run more efficiently at lower output power than standard non-inverter based generators because they have the ability to throttle back when operating at low output. The Inverter can keep full voltage and proper voltage with the reduced engine RPM. Typical Alternators, the output frequency is directly coupled to the engine RPM. For example, small gensets 3,600 RPM=60Hz... If the engine throttled back, the alternator spins slower, and the frequency falls out of spec.

For the Honda eu2000i: Run Time per Tankful 4hrs. @ rated load, 9.6 hrs. @ 1/4 load (1.1 gallons of fuel) (also note: Honda used to spec., 15 hours @ 1/4 load per tank of gasoline--I guess that was too optimistic ).

• 1,600 watts * 4 hours / 1.1 gallons = 5,818 WH per gallon at 100% load
• 400 watts * 9.6 hours / 1.1 gallons = 3,490 WH [per gallon at 25% load

So, from a cost of fuel point of view, you are better off running the Honda at higher loads if possible. Would it be better for the life of the engine to run it 6 hours at low load vs 3 hours at heavy load? I don't know--but I would tend towards running at heavier loads (just keep up with the oil changes).

The little Honda engines last a pretty long time when compared to other small gensets (these small genset Honda engines are not really rebuild-able as I understand--scrape and get another when they fail after X,000 hours).

Here is a nice thread: small generator questions -- In there, it sounds like you can get 1,500-3,000+ hours with a well taken care of Honda euX000i genset (oil changes every 50 hours from one user).

I read another post and believe I can get there with the DLS-27-25 @ 675 watts. I desire the headroom that this would give so other items could be operated while charging the batts and also to baby the genset while charging the batteries alone.

OK, 27.2 volt and 25 amp ouput... 80% efficient and 12 amps at 108 volts...

So, from a spec. point of view, the Honda eu2000i has enough current to drive the Iota Charger at full load:

• 12 amps * 108 VAC/117 VAC typical = 11 amps typical
• 675 watts maximum output power * 1/0.80 efficiency = 844 watt load on genset

Now, the battery charger will only output maximum current / power when the battery is below ~80-90% state of charge... So, you will want to monitor the charging current and battery state of charge (battery monitor) and probably cut off the genset when the charging current falls well below 10 amps (in terms of optimal fuel consumption).

For a rough estimate of run time to full charge--assume around 1-6 hours of absorb time (the last 10-20% recharging at reduced current).

My guess, is plan on recharging along this formula:

• Time on Generator = AH used / Amp Charging + 2 hours

So, for your three days of x 1,500 WH per day at 24 volts, I would try:

• 3 days x 1,500 WH * 1/24 volt battery * 1/25 amps charging + 2 hours = 9.5 hours

Measure the battery bank state of charge at the end of the 9.5 hours of charging (hydrometer, battery monitor, or resting voltage) and see how full the battery bank is...

I would not aim for 100% state of charge, but at least close to 90% will be fine... If the state of charge is a bit low, then add another 1-2 hours run time and see how things look.

Monitor the charging current at the end of the charging cycle (no use running the genset for a couple amps of trickle charging current). You have solar, so you can let it finish the charging the next time you have some good sun.

I don't know--perhaps it is just me, but it seems to be very difficult to find a reasonable battery charger that can pump out ~29 volts to quick charge a battery bank on a genset (assuming that it not too much current for the battery)... ~27.0 to 27.2 volts seem a bit low when trying to make the best use of generator run time and fuel costs (perfectly OK for a grid powered application).

Xantrex has some nice battery chargers that are at least 28.8 volts nominal output for charging a 24 volt bank as well as true 15/30+ volt equalization--But they are not cheap.

The only really programmable battery chargers seem to be those that are part of the inverter/charger families of Xantrex, Outback, Magnum, etc... And all of those are not going to be cheap either.

I do wish the Iota had an option for increasing their output voltage for those folks using gensets to push the charging current a bit harder.

Anyone else have a better suggestion?

-Bill

Re: Question about battery charger selection with EU2000 generator.

Thanks Niel, fixed (note to self: always use calculator :roll:).

Regarding Iota--Their battery chargers are not Power Factor Corrected (at least the models we are looking at here)... They probably have a current waveform with sharp peaks instead of a nice, in phase with the voltage, current sine wave...

This causes very high peak currents which raise the over all RMS current numbers (RMS--Root Mean Square value of current). So, the non-PFC power supplies appear to take more current, but not energy... So from the numbers, Iota claims 80% efficient. And we see 12 amps at 108 volts. We can back out a Power Factor calculation:

• Power to battery bank = Volts * Amps * Efficiency * Power Factor
• Power Factor = Power * Efficiency / (volts * amps)
• PF = 675 watts output * 1/0.80 * 1/(108 volts * 12 amps) = 0.65

So, the "apparent" amount of current used by the non-power factor corrected power supply is ~1/0.65 or 1.54 increase in current draw from the genset.

This extra 54% more current is totally unable to do any useful work... All it does is cause (I^2)*R resistive heating losses in the wiring and generator electronics.

So to put this all in an equation:

• P=V*I*eff*PF
• I ac input current=P/(V*eff*PF)=675 watts output to battery / (117 volts * 0.80 eff * 0.65 PF) = 11.09 amps

Which agreed with my earlier estimate of 12 amps*108v/117v=11.07 amps (close enough for government work / back of the envelope engineering calculation).

Anyway, one of the other reasons I like the Xantrex TC and XC inverter (Power Factor Correction) and many of the new inverter/chargers that also have power factor correction.

So, even though one would have expected from a "nice" AC power supply:

• Current from genset = 675 watts * 1/117 volts * 1/0.80 power supply efficiency = 7.2 amps

In real life with the older non-PFC power supplies (PF~0.65 in this case) we see it drawing an RMS equivalent current of ~11 amps...

And that extra ~5 amps AC input is totally wasted. It is not doing any real "work" and you cannot use that extra 5 amps to run a washer, fan, etc... Because it is it being "used" by the power supply.

-Bill

PS: Thanks again Niel--2 errors in three lines... Get some sleep...

Re: Question about battery charger selection with EU2000 generator.

Steve,

You probably need to call Iota to find out the exact operation of the DLS series...

Yes, there is a jump. IN=charging, OUT=Float (it appears).

The pdf manual seems to fall all over itself avoiding saying what the voltages are when the jumper is in/out.

TWO-STEP VOLTAGE JACK
The two-step voltage jack (located on the top of the DLS on the fan-end of the unit) allows switching from a long-term float voltage to an increased quick-charge voltage.

When the included dual voltage plug is inserted in the jack*, the voltage increases for faster charging. When the plug is removed, the voltage drops to rated nominal voltage to reduce battery water loss. WARNING: To avoid battery damage, remove the Dual Voltage Plug when quick-charging is complete.

NOTE: If the DLS is equipped with an internal IQ4 smart charger, two-step charging is not needed and the Dual Voltage Jack is disabled.

However, they do list the IQ4 as having:

float 2.26 volts per cell
Absorb 2.36 volts per cell
Bulk 2.46 volts per cell

So, which of the above three voltages map to the Jumper controller output... If the Jumper=IN=2.46=29.52 volts for a 24 volt battery pack--That is a very nice high voltage for quick charging on a generator.

If it is 2.36v*12=28.32 volts... A much more leisurely charging voltage (14.16 at 12 volt) and could end up costing you extra fuel.

Not to pick on Iota--Finding PFC battery chargers seems to be few and far between.

-Bill

Re: Question about battery charger selection with EU2000 generator.

Looks interesting... Has a battery temperature monitor (important if you are going to "push" the batteries or the bank is subject to temperature extremes. Nice high charging voltage of 2.55 volts per cell (30.6 volts). The F5 allows you to program your voltage set point--may be useful for optimizing your lead acid charging.

Questions I would ask:

1. AC Operating current seems like it may be Power Factor Corrected... Is it? What is the VA rating of the charger? I am not sure that it is (usually PFC is a wide range input from ~100-264 volts and covers 50/60 Hz with a single unit--these do not seem to have that ability).
2. What is the min/max input voltage range for proper charging (at full load)?
3. Programmable set voltage and gassing times?
4. Can F5 be used to charge 24 VDC lead acid with adjustable set point voltage?
5. Can unit be left connected to battery bank when AC power (generators) are off (what is leakage current through charger)? Since it is designed for on-board charging (manlifts, etc.)--I would guess it should be fine permanently connected to your battery bank.
6. What is the frequency range it will accept (i.e., 60 Hz +/- 1%, or 54-66 Hz for non-inverter style generator?

Assuming reliable charger from a reliable company (and the above questions are answered to your satisfaction)--Looks like would work very nicely for your needs.

At least one of the other general purpose models reads charging current... If you do not have a Battery Monitor or other current monitoring device--it might be nice to have so you can check/adjust your charging time/profile to minimize fuel usage (units usually turn off/go to float at 20% charging load current).

-Bill

Re: Question about battery charger selection with EU2000 generator.

Just one last warning (I don't think I said this regarding your project)--Charging your battery bank > 30 VDC may exceed the input voltage limit for some devices (inverters may shutdown, possible damage to others).

You may have to install a battery bank switch to allow you to disconnect sensitive loads during fast charging... There are also other options (run loads on bank A while fast charging bank B, etc.).

-Bill

Re: Question about battery charger selection with EU2000 generator.

SteveK wrote: »

Their units are not PF corrected. I made him repeat himself several times when I asked him to verify the unit would produce in excess of 1200W using only 11A 117Vac. According to them it will indeed with a voltage tolerance of +/- 3Vac.
...
He did not have the VA rating of the charger. I wonder if one could derive that through the published specs?

Eff or PF = 1200 watts / (11 amps * 117 volts) = 0.93

Really good battery chargers seen to reach around 90% efficiency.

"Average" non-PFC corrected battery chargers are probably in the 0.6 to 0.7 PF range.

PFC Corrected supplies are in the 0.95 or better range for Power Factor.

I have a bit of difficult time believing their spec.

Either it does not output 40 amps at 30 volts or it draws more than 11 amps RMS at 117 volts would be my guess.

You might have a difficult time getting the right answer out of them. A true RMS meter would be required to at least give you the VA rating.

The only programmable variables are the menu select functions. He did not feel that the LiIon function applied well to the lead acid variety at all. He suggested F2 "Gas & Timed Shut Off" and to stop the cycle short of a full routine if desired. Kind of hokey way to go maybe?

http://www.quickcharge.com/Images%20and%20PDF's/charge%20curves.pdf

That's all I have. Wish I had more. Do you guys get a warm and fuzzy from any of this?

Hmmm... The charging curves are not what I had hoped... Basically maximum charging current until the Vset-point is reached, then tapering down current to the 10-20% cutoff point.

[FONT=Fixedsys] Ibatt      Vbatt
++++++++oooooooooo Vset/Max current
       o+
      o  +
     o    +
    o      +
   o        +
  o          +
oo            ++++ Max Batt voltage / near zero current[/FONT] @100% SOC

I am not sure I understand the descending current with the ascending voltage.

I think the Iota has a charging profile more like I graphed above (they appear to have ~0.2 volt rise between 100% current and 0% current--I think that is at 12 volts, 24 volts should be 0.4 volt output voltage rise).

I do suspect that this gives an answer about the above "assumptions" of 1,200 watts at 93% efficiency...

Take the curve from the PDF--2.08 volts per cell * max current of 40 amps:

• 2.08 volts / cell * 12 cells * 40 amps = 998 watts into battery (not 1,200w)
• 998 watts / (11 amps * 117 volts) = 0.77 overall PF*EFF rating...

Closer to what I would expect--but still "better" PF*EFF than I would expect. Perhaps my one of my assumptions is still wrong here (not 40 amps?).

I think they are not near the PF*EFF that we are hoping for:

• 85% eff * 0.95 PF = 0.81 Output / input VA rating or better

But, I am not a battery engineer--So what I "expect" may not have any footing in reality. But the numbers still do not "look right" for what you are asking for.

This company offers a charger that does what I would like to see (PDF) (0.90% efficiency; 99 PF, 95 to 260 VAC, 45/65 Hz), --But they are limited to 10 amps for the 12/24 volt version (I think)... If they were cheap enough, perhaps 4 of them would be a solution (and offering some redundancy).

-Bill

Re: Question about battery charger selection with EU2000 generator.

The effective output resistance of the QuickCharge is (from the charging profile):

• 12 cells * (2.55 volts - 2.08 volts) / (25 amps - 0 amps) = 0.2256 Ohms

Whether there is a "real resistor" or just the result of the controller's internal electronics (feedback loop) does not matter too much (a real resistor wastes heat/energy, feedback control does not)... But this is, IMHO, a step backwards.

As a comparison--any descent sized battery bank you are looking at is probably going to have a resistance in the milli-Ohm range (0.00x Ohm). So the charging curve is a design choice by the manufacturer (from what I see).

Normally, a battery charger (as I would expect) should be in current limit mode (i.e., 30 amp current regulator) until the battery voltage rises enough to hit the voltage set point--at that time, the battery charger becomes a constant voltage regulator. When the current falls to XX% of rated current, then the charger turns off / goes to lower voltage float mode charging.

Regarding the Xantrex TC2 charger--I think the ratings are correct, but at 90 VDC (using nominal ratings):

• 13.5 amps * 104 volts * 0.85 eff * 0.95 PF / (28.8 volts charging) = 39.4 amps
• 13.5 amps * (104-4 min rated input AC) volts * 0.85 eff * 0.95 PF / (31+0.675 volts charging Lead Cadmium + cold offset) = 34.4 amps estimated output current

So--if we look at the input voltage extreme, the 13.5 amps looks reasonable for a 30 amp regulator at extreme low input voltage and maximum charging voltage*rated current...

For a 117 volt input and 28.8 volts at 30 amps:

• 28.8 volts charging * 30 amps * 1/0.85 eff * 1/0.95 PF * 1/117 volts = 9.1 amps

VA rating should be:

• 13.5 amps * 100 volts = 1,350 VA (+/-?)

The "load factor" or Watt output / VA = 0.85 * 0.95 = 0.81 or 1/0.81 = 1.24 ...

So, I think the TC2 does what you need, at the input current you would like (for a Honda eu2000i) and the output voltage has several ways you can adjust (choose Lead Calcium for 31 volt charge, or choose "cold battery" for +0.675 output voltage increase) or even (per PDF Manual):

2.The charger can be programmed with custom charge setpoints using PC interface. This programming can only be done using a special configuration tool operated by Xantrex or a designated OEM.

The only thing that paying more money may get you is 0.90 eff * 0.99 PF = 0.89 load factor (or 1/0.89 = 1.12)... How much would cutting 117 volt input current/fuel usage by 12% vs the hours saved with the TC2 (or other constant current/constant voltage 30-40 amp charger) be worth?

The only thing missing from the TC2 (that I can see) is the the programmable AC input current limit (like can be done with some of the Inverter/Chargers) and the ability to program exact charging profiles in the field (must be by OEM/Factory).

At least, as far as I can tell, the TC2 specifications are self consistent (at least to within a 10% or so range--I am guessing 30 amp output at 31.675 volts--that may not be true).

Could you run into some issue between the Honda eu2000i and the TC2 24v*30 amp charger--possibly--I just don't know. Unfortunately, you need to either test the setup yourself or find somebody that has done this setup successfully.

-Bill