Gen Set Question

MexDog · July 2010

I’m livig off grid in mexico with a very basic system (4) 165w panels, Outback 60cc, Zantrex 1500w modified sine inverter, and (4) trojan 105’s in series at 24v). 9 months of the year I have plenty of juice however the rainy season has begun and I’m looking to add a gen set to supplement. My question is: what size will be appropriate for this system? I want to optimize the size to have the shortest possible charging time without wasting money on a generator that exceeds the system’s capacity/charge rate.

Thanks!

Dan

icarus · July 2010

Re: Gen Set Question

A honda Eu 1000, powering a Xantrex TC 20 would be the perfect set up. The genny will put 20 amps into the battery, using less than 1 litre of fuel in 6 hours. The TC series isn't made any more, but they are widely available. (The EU 1000 won't run the larger TC 40 however due to power factor issues). There is a new version of the TC but it seems to be hard to find.

Iota makes a great charge as well, but I can't remember if it will run off the Eu 1000 or not. (Eu 1000 is very quiet as well).

Tony

mike95490 · July 2010

Re: Gen Set Question

So, you need to figure the max charge rate for the batteries, (2 in parallel), say it was 20A, So you need to charge at 40A @24V (28V) = 1120watts. So you need a charger that has good power factor (PF), and can do 40~50A. Then a genset about 20% higher capacity than that. Are you at sea level, or any altitude, that affects genset output too. My first guess is somethign in the 2,000W class with a good charger would do it. (but caculate on what YOUR batteries can take for charge current) Bulk charge on genset, PV to top off.

BB. · July 2010

Re: Gen Set Question

The reasonable rule of thumb is ~5-13% of the 20 AH rating of your battery bank. Your bank is 225 aH @ 24 volts:

225 AH * 0.05 = 11.25 amps minimum
225 AH * 0.13 = 29.25 amps maximum

Going under 11 amps is not really recommended if you want to use your generator for equalizing... But your solar panels can do that too--So not a limitation for your setup. Assuming 10 amps minimum and 30 amps reasonable maximum, and 30 volts maximum into charging the batteries:

10 amps * 30 volts * 1/0.80 charger eff * 1/0.6 PF = 625 VA
30 amps * 30 volts * 1/0.80 charger eff * 1/0.6 PF = 1,875 VA

Note that VA is either equal to or greater than Watts (VA=Watts when PF=1.0).

The Xantrex TC2 products are power factor corrected (PF~1.0). But they do not have a 24 volt unit--so you would be looking at 2x 12 volt units to charge your battery bank... Even though the TC2 look very nice--I am not sure I would do that (2x the price, 2x the things to go wrong--just a personal concern--others may disagree). Although, the remote battery temperature sensor, programmable output options, etc. do look very tempting even with 2x for your setup...

The Iota are not PFC, so you will have to use a larger genset for the same amount of power into the battery bank.

The above numbers are minimum genset Watts/VA rating--would not hurt to have 2x the above numbers for long life and allow for starting loads and running other AC devices while charging the battery bank (much more efficient to power AC loads directly from the Genset vs Genset-Charger-Battery-Inverter).

Running a generator below ~50% load will not reduce fuel flow siginificantly (the Honda euX000i family is a bit better at 25-50% rated power output--but not perfect either)...

From NAWS (our host), the Iota seems to be your best option at 24 volts (15, 25 amp versions available). You do not need the IQ-4 option. (there is a jumper setting for "charging" or "floating" your battery bank... You want the jumper in for charging. Float is for Utility Powered battery backed systems.

So, any 24 volt (or 2x 12 volt) setup at 10-30+ amps would be fine. Look at gensets at the same time, probably rated at 2x the calculated VA above (if PFC, use 1.0 instead of 0.6 for PF in above formulas).

If you get a diesel genset, running above 50-60% output load is pretty much required for long engine life and preventing carbon / coke formations in the engine (if operated with light loads).

Pick a couple combinations of charger/gensets (what is available in your area) and see what looks best for you. And ask here if anyone has run the combination (for example, running a 20 amp 12 volt charger is fine on a eu1000i, but a 40 amp non-power factor corrected charger is too much (per Tony/Icarus' experience).

-Bill

PS: I was just on the Honda Generator Website, and they have reduced the spec'ed run time for the eu2000i gensets at 25% load--It used to be 15 hours for 1.1 gallons of gasoline. Now, it is 9.6 at 1/4 rated load for 1.1 gallons of fuel.

I am guessing that 9.6 hours of runtime on a tank of fuel at 1/4 load is a much more reasonable number (

) for fuel use.

icarus · July 2010

Re: Gen Set Question

Bill, et al,

Just be clear,, The Xantrex TC 20 (20 amps into 12 vdc) works great with the Honda Eu 1000. It's sister, the TC 40 (40 amps into 12vdc) won't quite run on the Eu 1000.

I have the identical set up as the OP,, 4 T-105's in series parallel. The TC-20 putting 20 amps into the 450 ah of battery works out to be just under 5%. Couple that to ~25 amps of PV and were golden. The only time I use the genny is if we have had a number of grey days (or unusual loading) and the battery is ~80% soc or less, and there is little prospect of getting 100% back the next day. In my world, that happens about 10 days per year.

Tony

BB. · July 2010

Re: Gen Set Question

Sorry Tony,

You are correct and thank you for noticing

... I made a typo--that was supposed to be 40 amps at 12 volt battery charger is too much for a eu1000i.

Fixed in original post.

-Bill

MexDog · July 2010

Re: Gen Set Question

Thanks All,

A lot of the response info is way over my head, and I will be limited on purchase options here in rural mexico. I don't think Iota is an option and the Honda model numbers will probably be different here. I'm also not sure what the 2 x 12v references are for.

I'm running the Xantrex TR1524 and assume the charging will be handled at 24v. Is this incorrect? I do want the option of using the gen set for equalizing. At this point it sounds like I'll be fine with a honda that can muster 24v/20A will be fine. Is this correct?

Thanks,

Dan

MexDog · July 2010

Re: Gen Set Question

After reviewing the Xantrex TR 1524 manual more thoroughly, it seems as though I'll simply be running a 120AC single phase (or 240 w/ transformer) directly to the TR 1524 inputs from the gen set. The breakers specified for the TR 1524 are 20A for battery charger and 30A for pass through, so again, I'm assuming that any AC gen set with 20-30 Amp output (2-3KW) should be fine for this application. Correct?

One question though. The TR 1524 has an auto shutoff after 1 hr of equalization charging. This seems extremely short as most equalization charging I've heard of is more in the 6-10 hour range. Can anyone explain what the TR 1524 is doing here to make the equalize time so short (in lay language)? Would I actually be better using the Outback60cc to equalize from solar (probably over a period of several days due to inclement weather)?

Thanks!

BB. · July 2010

Re: Gen Set Question

You should only equalize when the battery bank needs it... Basically when the cell specific gravity is around ~0.030 or greater differences between cells. Check the SG every 30-60 minutes and as soon as the cells stop increasing SG--stop charging.

The very long equalization charge times, as I have read here, are only recommended if the battery has become heavily sulfated (lost capacity) and you are trying to recover capacity.

More of a "give it a shot" to see if you can help your battery--not something that you should ever do every month.

Equalization is very hard on a battery bank and doing it too often or too long will shorten the bank's life.

-Bill

MexDog · July 2010

Re: Gen Set Question

I've had the system up and running for over a year and have never equalized because the specific gravity between cells has been within acceptable ranges and everything has been running smoothly. This trip back here I'm finding all cells quite low specific gravity and they seem to be very slow coming back up. the system is only producing aprox. 1.5 KW/day because of cloudy weather. I figured Id give it a maintenance equalization charge to clear any sulfation there might be even though all cells art still nearly equal specific gravity. Does this seem like the right approach? Would the 1 hour Xantrex charge using a gen set be better, or a longer solar equalization?

I also need the gen set for supplemental charging during rainy season so plan on getting one anyway, which leads back to my initial question about the gen set sizing: am I good to go with any Honda 120 AC output in the 2-3KW range???

Thanks!

BB. · July 2010

Re: Gen Set Question

It looks like the TR 1524 charger output current is adjustable... So, any genset from 1,600 2.5/3.x kW should be fine.

The rest is probably your personal preferences... Me, I like small (fuel efficient operatoin) and quiet. But a Honda eu2000i is not cheap. And if you only run it a couple times a week for a month or so of bad weather--it may not be cost efficient.

On the other had, if you have heavier loads to support (power tools to add on to your place, shop, etc.)--then a bigger/nicer genset (diesel, propane, whatever makes sense for your area) may be a better investment.

Or--get a small / quiet genset for for battery charging, and a second larger / cheap and/or heavy duty genset for occasional heavy loads (and even backup power if important).

I am not sure what to say about your battery bank... Just charge it to 90%+ state of charge and cycle as normal.

If you need/want to equalize, charge until the SG stop changing (log temperature corrected SG -- this is your full charge). I would not continue to pump more energy into the bank unless you have see your battery bank capacity is way less than it used to be.

Others here can probably give you better advice than I.

-Bill

dwh · July 2010

Re: Gen Set Question

Some specs I saw for the Xantrex 1524 (the older one TR? Not the TC anyway...) say that the *max* it pulls when charging only is 10.2a. So if all you are running is the charger (not charger + loads connected to the inverter) then yes, a 2kw gen would be fine.

If you need to run the charger + loads running off the inverter you might need to go up to a 3kw. Keep in mind that a lot of generators are named after their surge load, not their continuous - i.e., the Honda Eu2000i is only good for 1600w continuous, and 2000 surge.

MexDog · July 2010

Re: Gen Set Question

Thanks. That's all clear now.

FYI, we had a pretty good day of sun yesterday and the batt's seem to be coming back, albeit slowly, from there discharged state. The cells are still measuring very even, which leads to my last equalizing question:

BB commented that equalizing should only be done when needed. The Outback manual says "Occasional equalization extends the life of fl ooded electrolyte batteries." And the trojan manual says "equalizing only when batteries have low specific gravity, below 1.250 or wide ranging specific gravity, 0.030, after fully charging a battery."

Given all this, I think I'm due now because of the heavy discharge state I went through, but I'm also wondering if I should have a regular maintenance equalization charge scheduled, or go strictly by specific gravity disparity.

BB. · July 2010

Re: Gen Set Question

Welcome to the wonderful world of lead acid batteries...

If you have not equalized for a long time and have no chart of per cell SG when 100% charged--I would choose a convient time and 1. fully charge the battery bank, then 2. equalize checking the SG every 30-60 minutes of each cell. When you don't see the SG rising... Stop. Log those readings as 100% state of charge for each cell.

Now you can monitor your bank and see when the 100% full readings deviate from your equalized 100% full.

If you get your battery bank recharged over 90% twice a week or so--you are doing fine. (and avoid having batteries set below ~75% state of charge for more than a day +/-...).

-Bill

Gen Set Question

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