Re: [RE-wrenches] Cable Sizing - revisited, Ambient Temp
Dave, Thanks for responding in Mr. Brooks place. Since ASHREA 2% is not the very worst case, it seems like it might be possible for the ampacity of the wire chosen to dip below the rating of the OCPD protecting it, if there is not much margin. I've been trying to rationalize whether this would become a safety issue. I don't think it would since the OCPD protects the wire from a current source increasing beyond the expected design output. I don't think there is much chance of that for a PV module (unless there was a short between two strings). I think the increased heating would more likely increase wire resistance/voltage drop and lower production. With enough voltage drop, the inverter might shut off. I guess my new concern is in the most severe case where there is solar concentration on a short section of conduit. Here, the heating effect of both the elevated ambient temp and reduced wire resistance might lead to premature failure of the wire insulation. If the combined heating effects exceed the 90C rating of the wire, does the insulation embrittle or melt? In either case, I foresee a grounding fault, and if the GFCI failed, it could spark a fire. I know the best solution is to keep conduit shaded and avoid these worst case solar concentrating conditions. Sometimes. when I design a system for a new contractor, I don't always know exactly where they plan to run conduit on a roof (nor can I control it) and I start "what-if'ing" whether my design numbers will be conservative enough to prevent a system failure or a fire. Thanks and regards, John Wadley, PE NABCEP Certified Solar PV Installer (TM) Wadley Engineering > Date: Tue, 25 Jan 2011 15:37:20 -0500 > From: Dave Click > To: re-wrenches@lists.re-wrenches.org > Subject: Re: [RE-wrenches] Cable Sizing - revisited, Ambient Temp > Message-ID: <4d3f3480.9030...@fsec.ucf.edu> > Content-Type: text/plain; charset=UTF-8; format=flowed > > John, > > The 2% "ambient temperature" from ASHRAE is the appropriate starting > point to use for these calculations. For some additional background I'll > quote Bill: > > ** > ASHRAE bases its ?warm?season temperature conditions? for each city on > annual percentiles of 0.4%, 1.0% and 2.0%. As an example, the June 2.0% > dry?bulb design temperature for Atlanta is 91.7?F. Therefore, based on a > 30?day month (i.e. 720 hours), the actual temperatures can be expected > to exceed 91.7?F a total of 14 hours a month. The corresponding 1.0% > design temperature (93.1?F) can be expected to be exceeded for 7 hours a > month; while the 0.4% design temperature (94.6?F) can be expected to be > exceeded for 3 hours a month (column 2). > ** > > In Jim Dunlop's example it sounds like he's starting with the summer > ambient high (likely around 90F / 32C) and adding the 310.15(B)(2)(c) > 33C figure to reach the 61-70C range. > > IMHO, ASHRAE 2% high temperature should be the "standard practice" for > these conditions when calculating your base ambient temperature before > additional adders. There are going to be site-specific conditions like > your example where the conduits may heat up more than 310.15(B)(2)(c) > requires; in that case I think you'd be on the right track to make your > own field measurements to determine an appropriate temperature. In some > cases the 10%/10ft rule may mean you can ignore short hot spots in the > wire. If you had a situation where the conduit was in direct sunlight, > plus light was being reflected off the roof and a light-colored wall > behind the conduit, I suppose that would yield more heating than what > the CDA study had found (http://www.iaei.org/magazine/?p=1743). I'm not > sure that shooting an IR thermometer is the best option here; if you > want to best replicate the study conditions, you may put a conduit > section up on the roof in the desired location, put a temperature sensor > in the conduit, and let it soak. Then compare that number with [ASHRAE > 2% + 310.15(B)(2)(c)] and pick the higher number. Or just add an > additional 10C on top of ASHRAE+B2c and be done with it... > > I think your plan of trying to measure the temperature 4" off the roof > where the conduit sits, and then adding the additional 17C (or whatever) > from the Table, will be too conservative; your initial measurement will > be affected by some of the heating that's wrapped into the > 310.15(B)(2)(c) factor and you'd be double-counting that effect. > > Hope that helps. > Dave > > Original Message > Subject: [RE-wrenches] Cable Sizing - revisited, Ambient Temp > From: John Wadley > To: RE-wrenches > Date: 2011/1/22 02:40 > > > Mr. Brooks, > > You replied to Mr. Parrish back in 2009 with this example (below) on > > properly applying all the deratings to ampacity for wire sizing. I have > > a bit of confusion and a question about the definition of "ambient > > temperature". You define it below as the ASHREA 2% high temp. My
Re: [RE-wrenches] Load testing batteries?
Hi Jesse, I see you have already received several responses to your post. Only one item to add. Given the electrolyte was dumped and replaced with "new" you SG readings will be artificially high and am surprised they are reading ~1.225. I surmise that low strength acid may have been added? Suggest you charge these units until the SG stops rising. As mentioned by many, please be careful as the freezing may have caused internal shorts, which you should notice as soon as you place on charge / discharge. Regards, Jamie >>> Jesse Dahl 1/26/2011 1:53 AM >>> Wrenches, I have some (4) rolls 6 volt batteries 4000 series S-460. They are from a stand alone system in Ely, MN I have mentioned in a previous question. I had mentioned in the previous post that they were suspected to have been frozen (bulged cases). The owner took them out of the system, dumped the electrolyte out and added new electrolyte. I have no idea what she added or any specifics. I did a SG test today, all of the cells seemed to have 50% SOC, but I don't think that means anything. Most of the info I got from the last post and from my knowledge tells me the batteries are shot. They are 10 years old at least. What I'm asking, I guess, is what type of load tester would a person need to load test a battery like this. I have a cheap one, up 160Ah I believe, but I'm not sure if it will work this test. I have limited battery experience and would appreciate any help with testing methods. Thanks everyone, Jesse Sent from my iPad!!! ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org This email and its attachments have been scanned by iConnection E-Mail Firewall for viruses, spam, and malicious content. The information transmitted in this email is intended only for the entity or person to which it is addressed and may contain confidential/privileged material. If you received this in error, please contact the sender and delete the material from any computer. Any review, retransmission, dissemination, or other use of this information by persons or entities other than the intended recipient is strictly prohibited. %^^% ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] Load testing batteries?
My "Brand" brand kWh meter has non-volatile capture of the kWh data even when power is removed. I assumed that was true of the other kWh meters, also, but one would certainly want to check on that point. Dan's other points are helpful. If the clock is left out of the setup , one could still get a useful capacity number for the batteries. Batteries are rated in amp-hours...not watt-hours, of course, so there is some conversion math to be done. Similar testing could be done with an amp-hour meter on the DC side between battery and load...and that would be more precise for a couple of reasons. My suggested setup does not account for inverter inefficiency, for example, so it will tend to understate the actual capacity. The big advantage of my original suggested test rig is that the needed items are less exotic and more usable for other purposes. If Jesse doesn't already own one of those plug in watt-hour meters, he probably wants a good excuse to get one. Ditto for the mini inverter. Jolliness, Mick Abraham, Proprietor www.abrahamsolar.com Voice: 970-731-4675 On Wed, Jan 26, 2011 at 8:42 AM, Exeltech wrote: > Once the electrolyte has been changed out, all bets are off for using SG as > an indicator for state of charge. Jamie Surette gave excellent commentary > on a similar thread recently on how to handle a situation such as this. > > Mick's suggested procedure (below) will work, with caveats. > > Be sure you use a meter that records accumulated watt-hour usage in > non-volatile memory. You'll be connecting the meter on the AC-side of the > inverter, and when the AC goes off due to low DC input voltage, the meter > will go off as well. The basic Kill-A-Watt meter (and perhaps others?) > forget everything when the power goes off. P3 (mfgr of the K-A-W meter) > make a model P4460 that "remembers" values even when powered down. Others > likely do as well. > > I would recommend using incandescent lamps as a safer and more easily > adjustable load. Parallel three 100 watt lamps on a power strip. With a > meter (above) measure the actual power drawn by the lamps. > > As a backup "timer" for testing batteries, I use an ordinary analog clock > .. the type with moving hands (remember those?). Got mine from a big-box > store. It uses 3 watts, so is an insignificant load compared to 300-400 > watts. Set the clock to 12 am and start your test. The clock will stop > with the total run time when the inverter shuts off. > > Speaking of inverters .. use a model that requires a manual reset after > low-voltage shutdown. Some types will automatically start back up if the > voltage rises high enough again. This could give you a bit of a false > reading as to total capacity > > Be careful. > > > Dan > > > --- On *Wed, 1/26/11, Mick Abraham * wrote: > > > From: Mick Abraham > Subject: Re: [RE-wrenches] Load testing batteries? > To: "RE-wrenches" > Date: Wednesday, January 26, 2011, 9:19 AM > > > Hello, Jesse~ Instead of trying for laboratory precision, here's a way to > measure the battery capacity using equipment that you may already own: > > * Gather up appropriate safety stuff: gloves, goggles, baking soda, > distilled water, off duty fireman, blast protection, etc. > > * Connect only two of the 6 volt batteries in series to make a 12 volt > battery string. Put those on charge once you're sure they're warmed up & > thawed out. Maintain about 75 degrees Fahrenheit air temperature in the > testing area. Recharge quality is important if you want to give the > batteries a fair opportunity to show what they can do. > > * Install a DC breaker between battery positive and the positive DC > terminal on a 12 volt inverter. The inverter should be 500 watts or bigger > with AC plug in receptacles; you can connect inverter negative to battery > negative & power it up on the DC side. > > * Plug into the inverter with an AC kilowatt-hour meter (such as > Kill-a-Watt, the Brand meter, WattsUp?, etc.) then plug into the kWh meter > with an adjustable blow dryer. > > * Switch on the hair dryer at a low setting then dial up on the heat until > your AC meter shows about 360 watts of power draw. The battery pair, if new, > should be able to sustain a drain like this for about ten hours--this is > based on the 298 amp-hour rate for that battery on the Rolls spec sheet. > > * Run the blow dryer until the inverter shuts off due to low voltage, then > read the number of AC watt-hours that were clocked by the kWh meter. 298 amp > hours X 12 volt nominal = 3,576 watt-hours. Battery professionals would > replace a battery if it fails to deliver 50% of the original rated power. > > * Repeat this same test with the other battery pairs. As mentioned, this > approach is not scientifically perfect, but it might be done with minimal > outlays for new equipment...and the results will be close enough. > > Jolliness~ > > Mick Abraham, Proprietor > www.abrahamsolar.com > > Voice: 970-731-4675 > > > On Tue, Jan 25, 2011 at 10:53 PM, Jesse D
Re: [RE-wrenches] Load testing batteries?
Once the electrolyte has been changed out, all bets are off for using SG as an indicator for state of charge. Jamie Surette gave excellent commentary on a similar thread recently on how to handle a situation such as this. Mick's suggested procedure (below) will work, with caveats. Be sure you use a meter that records accumulated watt-hour usage in non-volatile memory. You'll be connecting the meter on the AC-side of the inverter, and when the AC goes off due to low DC input voltage, the meter will go off as well. The basic Kill-A-Watt meter (and perhaps others?) forget everything when the power goes off. P3 (mfgr of the K-A-W meter) make a model P4460 that "remembers" values even when powered down. Others likely do as well. I would recommend using incandescent lamps as a safer and more easily adjustable load. Parallel three 100 watt lamps on a power strip. With a meter (above) measure the actual power drawn by the lamps. As a backup "timer" for testing batteries, I use an ordinary analog clock .. the type with moving hands (remember those?). Got mine from a big-box store. It uses 3 watts, so is an insignificant load compared to 300-400 watts. Set the clock to 12 am and start your test. The clock will stop with the total run time when the inverter shuts off. Speaking of inverters .. use a model that requires a manual reset after low-voltage shutdown. Some types will automatically start back up if the voltage rises high enough again. This could give you a bit of a false reading as to total capacity Be careful. Dan --- On Wed, 1/26/11, Mick Abraham wrote: From: Mick Abraham Subject: Re: [RE-wrenches] Load testing batteries? To: "RE-wrenches" Date: Wednesday, January 26, 2011, 9:19 AM Hello, Jesse~ Instead of trying for laboratory precision, here's a way to measure the battery capacity using equipment that you may already own: * Gather up appropriate safety stuff: gloves, goggles, baking soda, distilled water, off duty fireman, blast protection, etc. * Connect only two of the 6 volt batteries in series to make a 12 volt battery string. Put those on charge once you're sure they're warmed up & thawed out. Maintain about 75 degrees Fahrenheit air temperature in the testing area. Recharge quality is important if you want to give the batteries a fair opportunity to show what they can do. * Install a DC breaker between battery positive and the positive DC terminal on a 12 volt inverter. The inverter should be 500 watts or bigger with AC plug in receptacles; you can connect inverter negative to battery negative & power it up on the DC side. * Plug into the inverter with an AC kilowatt-hour meter (such as Kill-a-Watt, the Brand meter, WattsUp?, etc.) then plug into the kWh meter with an adjustable blow dryer. * Switch on the hair dryer at a low setting then dial up on the heat until your AC meter shows about 360 watts of power draw. The battery pair, if new, should be able to sustain a drain like this for about ten hours--this is based on the 298 amp-hour rate for that battery on the Rolls spec sheet. * Run the blow dryer until the inverter shuts off due to low voltage, then read the number of AC watt-hours that were clocked by the kWh meter. 298 amp hours X 12 volt nominal = 3,576 watt-hours. Battery professionals would replace a battery if it fails to deliver 50% of the original rated power. * Repeat this same test with the other battery pairs. As mentioned, this approach is not scientifically perfect, but it might be done with minimal outlays for new equipment...and the results will be close enough. Jolliness~ Mick Abraham, Proprietor www.abrahamsolar.com Voice: 970-731-4675 On Tue, Jan 25, 2011 at 10:53 PM, Jesse Dahl wrote: Wrenches, I have some (4) rolls 6 volt batteries 4000 series S-460. They are from a stand alone system in Ely, MN I have mentioned in a previous question. I had mentioned in the previous post that they were suspected to have been frozen (bulged cases). The owner took them out of the system, dumped the electrolyte out and added new electrolyte. I have no idea what she added or any specifics. I did a SG test today, all of the cells seemed to have 50% SOC, but I don't think that means anything. Most of the info I got from the last post and from my knowledge tells me the batteries are shot. They are 10 years old at least. What I'm asking, I guess, is what type of load tester would a person need to load test a battery like this. I have a cheap one, up 160Ah I believe, but I'm not sure if it will work this test. I have limited battery experience and would appreciate any help with testing methods. Thanks everyone, Jesse Sent from my iPad!!! ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.or
Re: [RE-wrenches] Load testing batteries?
Hello, Jesse~ Instead of trying for laboratory precision, here's a way to measure the battery capacity using equipment that you may already own: * Gather up appropriate safety stuff: gloves, goggles, baking soda, distilled water, off duty fireman, blast protection, etc. * Connect only two of the 6 volt batteries in series to make a 12 volt battery string. Put those on charge once you're sure they're warmed up & thawed out. Maintain about 75 degrees Fahrenheit air temperature in the testing area. Recharge quality is important if you want to give the batteries a fair opportunity to show what they can do. * Install a DC breaker between battery positive and the positive DC terminal on a 12 volt inverter. The inverter should be 500 watts or bigger with AC plug in receptacles; you can connect inverter negative to battery negative & power it up on the DC side. * Plug into the inverter with an AC kilowatt-hour meter (such as Kill-a-Watt, the Brand meter, WattsUp?, etc.) then plug into the kWh meter with an adjustable blow dryer. * Switch on the hair dryer at a low setting then dial up on the heat until your AC meter shows about 360 watts of power draw. The battery pair, if new, should be able to sustain a drain like this for about ten hours--this is based on the 298 amp-hour rate for that battery on the Rolls spec sheet. * Run the blow dryer until the inverter shuts off due to low voltage, then read the number of AC watt-hours that were clocked by the kWh meter. 298 amp hours X 12 volt nominal = 3,576 watt-hours. Battery professionals would replace a battery if it fails to deliver 50% of the original rated power. * Repeat this same test with the other battery pairs. As mentioned, this approach is not scientifically perfect, but it might be done with minimal outlays for new equipment...and the results will be close enough. Jolliness~ Mick Abraham, Proprietor www.abrahamsolar.com Voice: 970-731-4675 On Tue, Jan 25, 2011 at 10:53 PM, Jesse Dahl wrote: > Wrenches, > > I have some (4) rolls 6 volt batteries 4000 series S-460. They are from a > stand alone system in Ely, MN I have mentioned in a previous question. I had > mentioned in the previous post that they were suspected to have been frozen > (bulged cases). The owner took them out of the system, dumped the > electrolyte out and added new electrolyte. I have no idea what she added or > any specifics. > > I did a SG test today, all of the cells seemed to have 50% SOC, but I don't > think that means anything. > > Most of the info I got from the last post and from my knowledge tells me > the batteries are shot. They are 10 years old at least. What I'm asking, I > guess, is what type of load tester would a person need to load test a > battery like this. I have a cheap one, up 160Ah I believe, but I'm not sure > if it will work this test. I have limited battery experience and would > appreciate any help with testing methods. > > Thanks everyone, > > > Jesse > > Sent from my iPad!!! > ___ > List sponsored by Home Power magazine > > List Address: RE-wrenches@lists.re-wrenches.org > > Options & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out participant bios: > www.members.re-wrenches.org > > ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
