Generator usage

[extrafu]

Hello,

First winter here being off grid - things are going fairly well.

During bad days, with lots of snow and virtually no sun, I have to fire up the generator a bit (Kohler RESA 14 KW) to charge my batteries (Rolls S550, 6V/428Ah x 8, all in series).

If I know I'll get a few hours of sun, say 2 to 3, I usually fire up the generator until I see from the inverter amps are going down from charging. When the batteries are about 50 SOC, the inverter/charger (Conext XW 6848) generally pumps 65 amps in the batteries, slowing going down to 10 amps after a good 2 hours of run time. So when I see the current going down, I usually stop the generator and let the solar panels continue or even finish the absorb state, often even going into float for an hour or two during "ok days". Do you guys think it's a good strategy for good care of the batteries?

Also, how about in very continuous days - is it better to run the generator 2 hours straight for the whole day until the absorb state is reached (and a good hour into it) or would it be better to run the generator 1 hour in the morning and 1 hour at night to finish bulk charge and go into absorb?

Thanks!

[Mike90250]

I run my genset in the AM till I see some amps roll off and wast generator capacity, and if any sun peeks though, I get some absorb, If no sun, I'll run a bit in the evening/night if it's not raining, to postpone a trip in the rain in AM.

[extrafu]

Mike90250 Thanks, sounds pretty much like what I'm doing!

[Sunking]

Ditto run the generator in pre-dawn until the batteries reach Absorb stage ie when the charge current begins to taper and use solar to finish.

[SolarIslander]

Hi Extrafu

How do you like the Kohler RESA 14 KW? We are planning on purchasing almost exactly the same system that you are running, except perhaps using tubular 2V FLA batteries (although the Rolls S550 seem an good option until LiFePO4 becomes more cost effective and available here in Canada).

Our choice for a prime generator at the moment is wavering between the 4 kW and the 8 kW (which is reputed to be noisier, possibly due to being a single cylinder engine).

I've heard that the recently developed SW4024 (and SW4048?) have dual voltage input capable charging. This means that one could do bulk charge with a prime generator like the Kohler RESA 14 KW and then finish up with a smaller more economical 120 VAC inverter unit like a Honda i2000Eu. I gather that to switch generators like this, the max charge amps would have to be dialed back though when swiching the smaller unit.

I wonder if recent firmware models of the XW6048s allow 120 VAC charger input? This would be great as we already have a small 120 VAC generator.

Cheers, from SolarIslanders .

[Mike90250]

The XW can be set for 120V only or 240V only, I don't think you can have 240V output and only 120V charging. OR watch ebay for a PSX -240 auto-transformer. it can step up 120V to 240v and most generators (but sometimes not inverter generators) can use it to tun the 240V charger circuit

[extrafu]

SolarIslander So far so good with the Kohler RESA 14 KW. It has started flawlessly even when it was -20 to -35C recently. I don't where you're located in Canada (I am in Quebec) but one good place to shop is solacity.ca Rob over there is class-act and prices are pretty good.

[SolarIslander]

Good on the Kohler folks for designing for northern winters! I've heard that the bigger Honda inverters (Eu7000i etc.) that can do 120/240 don't start well in the cold. For us out on the more temperate Pacific wet coast of Canada the cold isn't so much of an issue. But gasoline seems to have an insatiable thirst for drawing moisture out of the air and condensing inside gen set fuel tanks! Draining the sump on gen set tanks is a regular ritual.

Too bad that nobody has designed a prime service type inverter gen set that can more efficiently handle both bulk charging and finish charging loads.

Certainly either a 240 VAC variant of the small Honda EU's or an autotransformer and a 120 VAC gen set would be useful for finish charging.

Still debating if a propane powered 14 kW is overkill for us on a 450 Ah 48 volt battery bank / 3000 W PV installation. Maybe a 8kW prime gen set is a better choice.

Our main issue is lack of sun in the winter/shoulder seasons leading to occasional battery bank saving auto-start requirements to deal with say 5 days of cloudy weather and our LG inverter fridge (1 kWhr/d load) running things down. We have things planned to install the fridge in a low ambient T area so the loads will be comparably lower in the winter as the insolation drops. This is a retirement cabin used part time year round.

[extrafu]

It might be a bit overkill for you. Note that my generator was sized for much bigger loads and next year, I plan to replace my Rolls S550 batteries (8) with way bigger ones (4 KS 25P or Trojan SIND 04 line).

Read this good Sunking post on generator sizing: https://www.solarpaneltalk.com/forum...069#post322069

Merry Christmas!

[Sunking]

Sun Islander the genny has two jobs.

1. Recharge batteries
2. Plus run all your daily loads.

So what might seem like overkill may not be. FWIW you do not want to use gasoline. Either LPG or diesel because you cannot store volumes of gasoline for extended periods. Plus try finding it after a natural disaster.

[Gakialla]

new here, sounds interesting , hope to try it one day
good luck

[SolarIslander]

Good points about genset sizing from Sunking and thanks for the link Extrafu: To summarise Sunking's earlier post on this at the link::

The size of the generator is determined by how much maximum load the generator has to carry. The correct size of the Generator = [Load + Charge Rate] x 1.25.

In other words if the connected load of say 3 Kw (your lights, fan or whatever is expected to be running), plus say a 5 Kw Charger you need a minimum 10 Kw generator. The charger is sized to charge the battery at maximum allowable charge rate for your battery to minimize fuel burn.

For a 6 Kw Inverter with an 80 amp built-In battery charger operating into a 48 volt 430 amp hour battery right. So if you figure 3 Kwh of lights and gizmo's running and a 48 volt 80 amp charger (4 Kw) you will need a [3 +4] x 1.25 = 8.75 Kva minimum generator. So now you go shopping for a 10 Kva genny.

Basically, if a larger battery bank is ever being considered that can accept a higher charge rate, the XW6048's 140 amp charge current capability suggests that the larger genset is the right size:

[140 Amp * 50 V = 7000 W + 3000 W loads ] *1.25 = 12,500 W.

One comment that caught my eye in Mike's post though that I underline below:

"watch ebay for a PSX -240 auto-transformer. it can step up 120V to 240V and most generators (but sometimes not inverter generators) can use it to run the 240V charger circuit"

Is the potential problem with small inverters and auto-transformers that their "eco throttle" function is not compatible with keeping the auto-transformer saturated, or is a transformer just too much of an inductive load for their control circuits to stabilize things enough to be accepted by an XW?

Hope the deep freeze back east isn't causing too many frozen fingers! (We've got freezing rain predicted tonight, out in the boat to the cabin tomorrow to finish construction ...)

Here's to Sunny Days to Come - SolarIslanders

[Sunking]

One comment that caught my eye in Mike's post though that I underline below:

"watch ebay for a PSX -240 auto-transformer. it can step up 120V to 240V and most generators (but sometimes not inverter generators) can use it to run the 240V charger circuit"

Easy enough to work around. Use a standard 2:1 transformer in reverse and step up 120 to 240. Nothing in code, listings, or practices to prevent someone from doing so. Common practice especially on long runs to step up voltage.

[Mike90250]

some inv gens are reported to not work well with the inductive load the transformer presents. It's not an auto-throttle issue, it's more likely a power factor issue, Attach unloaded xformer, inverter shuts off. reset, it trips off again.
My honeywell 2k inv gen worked fine with my surplus 10KVA transformer

[Sunking]

some inv gens are reported to not work well with the inductive load the transformer presents.

FWIW transformers may or may not appear to be inductive. It is totally dependent on the load.

If the load is pure resistance, the transformer is roughly pure resistance. If the load is inductive, the transformer sees roughly the same inductance of the load. So with a load connected, the transformer sees roughly the same resistance/Inductance as the load. It is only if the secondary is open (no load) does the transformer appears as pure Inductance.

If you would like to dig deeper, and having a hard time falling asleep, try reading this.