Solar Guppy Discussion Forum
http://solar-guppy.com/forum/

Battery Bank Size for 3k system with XW6048 Xantrex Inverter
http://solar-guppy.com/forum/viewtopic.php?f=20&t=774		 Page 2 of 2
Author:  mike90045 [ Sat Aug 15, 2009 6:56 pm GMT EthGMT ]
Post subject:  Re: Battery Bank Size for 3k system with XW6048 Xantrex Inverter
BigGuns wrote:
I got up before dawn (groan) and checked the battery voltage. Everything was connected, but there had been no grid failures, and the Charge Controller was still in the Low Light condition. The battery voltage was 10.9 volts. I think this must be close to the “resting” voltage.


The Deep Cycle Battery FAQ
http://www.windsun.com/Batteries/Battery_FAQ.htm

indicates that 10.9V :!: is very nearly completely discharged, more than 90% discharged

This is generally VERY BAD for batteries to go this low. :(
Author:  BigGuns [ Sat Aug 15, 2009 9:57 pm GMT EthGMT ]
Post subject:  Re: Battery Bank Size for 3k system with XW6048 Xantrex Inverter
I sure wish I could type better. The morning voltage was 50.9, not 10.9. Sorry I screwed up again. This is on a 48 volt system, four Dekas in series.
Author:  Solar Guppy [ Sun Aug 16, 2009 2:16 pm GMT EthGMT ]
Post subject:  Re: Battery Bank Size for 3k system with XW6048 Xantrex Inverter
BigGuns wrote:
I sure wish I could type better. The morning voltage was 50.9, not 10.9. Sorry I screwed up again. This is on a 48 volt system, four Dekas in series.


12.7V * 4 = 50.8V is a fully charged bank ... ANY voltage over this will be charging the battery's, they don't just start accepting a charge at 57.6V. The only difference is how long it takes to recharge, the lower the voltage, the slower the recharger but the more efficient the charge is.

BigGuns wrote:
If I set the sell voltage to 52, the SCC stays in Bulk mode all day. Is this what you are suggesting is correct?
Chuck.


Yes, its above the full charge resting voltage ...

BigGuns wrote:
We made sure to really minimize our electric usage, and I watched the battery voltage just to see if I needed to start the generator to power my wife’s oxygen support. To my delight the SCC charger kicked in and maintained the batteries, as well as supplying all the Inverter power we needed.
Chuck.


So, you have the capacity to go a full night and then rely on the solar to start recharging the battery's

OR

BigGuns wrote:
I understand about not needing to charge the batteries every day, I’m just not sure how to accomplish that feat. I don’t want to rely on my having to manually start the charger if a grid failure discharges the batteries.


Enable the Xw-6048's charger, set the bulk to 56V ( XW-MPPT should be 57.6V ) and select 2-stage charging. Also set the recharger level to say 48V, which would only happen when utility power is lost and when power returns the XW-6048 charger will do a charge cycle before grid-sell gets re-enabled.

http://www.xantrex.com/web/id/1871/docserve.aspx ( page 3-12 )

So, without power failures batterys are always charged, most energy is being sold to the grid ( 52V is more than 50.8V ) but little excess is being wasted. If power does fail, XW-6048 will start a charge cycle, but if solar is available the XW-MPPT with its higher bulk / aborb setting will take over that charging cycle if conditions permit
Author:  BigGuns [ Sun Aug 16, 2009 3:42 pm GMT EthGMT ]
Post subject:  Re: Battery Bank Size for 3k system with XW6048 Xantrex Inverter
Thanks, I believe I'm finally beginning to understand.
Author:  tools [ Tue Aug 18, 2009 2:55 pm GMT EthGMT ]
Post subject:  Re: Battery Bank Size for 3k system with XW6048 Xantrex Inverter
BigGuns wrote:

I assume you do not want the SCC charger turned off completely, as then how would the batteries ever get recharged should a grid failure occur?

If I set the sell voltage to 52, the SCC stays in Bulk mode all day. Is this what you are suggesting is correct?

If I set the sell voltage to 55, the SCC stays in Absorption mode all day. Is this better?



I'm not sure if you are confused about what it means when it says bulk charging. when the scc says bulk,it doesnt necessarily mean the batteries are charging,what it does mean is that full power from the solar array is coming through the scc.

batteries will only take so much charge,after they reach the proposed voltage on the scc,the excess will be sold off to the grid,so being in bulk mode is a good thing,as you do want all the power from the array to be sold off after the batteries are charged.

for my example I have a smaller battery bank,315 amp hours.Since my battery bank only wants to accept 51volts due to construction of the battery,I set my grid support volts to 51.8....this has been working really good and the voltage oscillation isnt as great as it had been.

in overview,52 volts setting for grid sup volts will allow you to sell all the power from your solar array while keeping your battery bank fully charged and maintained in case of power failure.
Author:  sub3marathonman [ Wed Aug 26, 2009 11:34 am GMT EthGMT ]
Post subject:  Re: Battery Bank Size for 3k system with XW6048 Xantrex Inverter
This is almost the same scenario that Solar Guppy helped me with.

One thing I don't understand though, if it is absolutely CRITICAL to keep these batteries happy, couldn't you just put an Automatic Generator Starter on the XW6048 so when the batteries reach a certain voltage the generator would start? I see that a generator is already available, but currently has to be manually started. I don't know too if that would allow for the smaller 200ah battery bank to continue as is even when more solar capacity is added.

I thought too that you could actually reduce the charging rate if you wanted to somewhere in the XW's or SCC's menu. So even with 6kw of solar PV, you could possibly still get by with the smaller 200ah battery bank? I guess this would waste PV capacity, but it may only be for small periods of time.
Author:  OldSonne [ Mon May 09, 2011 10:21 am GMT EthGMT ]
Post subject:  Re: Battery Bank Size for 3k system with XW6048 Xantrex Inverter
I have been using load sharing, but I have the grid support voltage set at 52V. The XW6048 charger is OFF. I just recharge from the sun, and it has been sunny every day for weeks. Of course, if my night time use draws down a few kwhours and it is cloudy in the morning it takes a while for the battery to recharge, but so what. I inquired about a firmware upgrade from Xantrex and got this advice which included setting the grid support voltage at 62VDC. Is there something in the new firmware that really would make going to such a high grid support voltage acceptable?

"Firmware release notes attached. You should be able to utilize Enhanced Grid Operation with 1.3BN12. Try setting Grid Support Voltage to 62VDC and it should do a better job of keeping the battery full. We have instructions for upgrading, but you would need the XW Config Tool (865-1155). You can call Tech Support and we can set you up with a loaner (866-519-1470). The settings should be retained."
Author:  AngelT [ Sun Aug 07, 2011 10:59 am GMT EthGMT ]
Post subject:  Re: Battery Bank Size for 3k system with XW6048 Xantrex Inverter
If money is not a problem, I will add another battery array and connected in parallel with the existing array for a total of 48 vdc and 400ah...
Author:  mike90045 [ Mon Aug 08, 2011 9:38 am GMT EthGMT ]
Post subject:  Re: Battery Bank Size for 3k system with XW6048 Xantrex Inverter
Be very careful when paralleling a new bank with an old one. Batteries should be identical, preferably from the same lot. Differences in internal resistance, will quickly (1-2 months) reduce the better performing bank, to the same performance/quality of the lowest performing bank.
Author:  OldSonne [ Mon Aug 08, 2011 11:46 am GMT EthGMT ]
Post subject:  Re: Battery Bank Size for 3k system with XW6048 Xantrex Inverter
Guys, thanks for the suggestions. I have given up on the idea of off grid for the common sense reason that there is no point in using all the energy to produce, distribute and recycle batteries when I can share my excess with others on the grid and get at least a reasonable credit of about 70% of full retail. I continue to work with the utility company to get to true net metering or some other way for solar investors to get more incentives. I appreciate all the advise and support! FYI, my net net zero home has produced about 1600 kwh more than used since moving in 15 months ago. So far, so good!
Page 2 of 2 All times are UTC - 5 hours [ DST ]
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group
http://www.phpbb.com/