Tweet
More like anger - at myself, but also some of the "guidance" I received. I understand that that 2000W/24V is the same as 4000W/48V.... what I missed in my planning was considering that I could halve the battery storage after I initially calculated my need... once I determined the 1500 capacity - everything started to be based on that (literally - in my spreadsheet). Dumb, I know. Go ahead and snicker..
-
-
I reckon when this battery dies, I'll just get the smaller AH / higher voltage battery and upgrade my inverter at that time. Yay.Comment
-
so what you meant was 2000WH/24V is the same as 4000WH/48V ?
This would be true if the AH is the same on the two battery banks
As Sunking pointed out
Originally posted by SunKingOutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNHComment
-
Not going to happen, and it may not be too late. Not sure we are on the same page. Let's make sure we are on talking apples to apples.
For batteries: Watt Hours = Battery Voltage x Amp Hours.- Are we on the same page now? Very important to understand that.
- So do you already have the batteries?
- If so what model and how many?
MSEE, PEComment
-
How I understood you so far... that 1576 AH at 24 V (37,824 WH) would be the same as 788 AH at 48 V (37,824 WH).
I have a 24v industrial battery with 12 2v cells (I think it's a GBI) . The terminals are not soldered/welded, but bolted so each cell can be removed. There are two banks (contained in one steel case) - each of 12V - wired in series. I don't believe 48V is possible with this. I can live with 24 V for the present btw.
Comment
-
Got a link to this battery? What is throwing me is GBI. Never heard of them. Could it be just GB? Just curious.
Anyway the part code does ring some bells. 6 tells me either 6-cells or 12 volts. SBY is manufacture specific but I suspect it means an Industrial Fork Lift Battery. 125-17 is an Industry Standard Form Factor Dimension of the battery. 125-17 is a Fork Lift and Telecom size.
Couple of pieces of info for you which you will like. Fork Lift and Industrial batteries have a different AH rating. Typically 4, 6, and 8 hour Amp Hours. That means if it is a 1575 AH Fork lift battery if discharged at C/20 becomes a much larger battery. of more like 2000 AH at the 20 hour rate. One reason i wanted to look at the specs. Additionally Fork Lift batteries can be discharge 80% DOD. They can also handle much higher charge and discharge rates. And they last longer.MSEE, PEComment
-
Hey Sunking - I don't have an exact link because I don't believe they list this particular one online (according to the vendor who sold it to me). I think it's a special/custom option because of the terminals. Here is a link that shows what I believe is the same exact battery listed as 12-125-17: http://gbindustrialbattery.com/Forkl...ns_Zone15.html.
The main difference with mine is that it has special terminals that are wired/bolted vs welded/soldered/cast or however they're usually connected. (see pics). More on that in a minute..
I was aware of all the points you made. One clarification - the 1576 AH is the 20 AH rating for the battery, though that is not the "normal" way forklift/industrial batteries are rated as you point out. I believe the 6 HR rating is 1000 AH and that is what the labels affixed to the batteries say.
I spent about two months researching batteries and built a spreadsheet to try to boil any prospective battery down to cost per ah. From what I could determine - which may have been incorrect, I confess - this type of battery was the most bang for the buck and the lowest cost per ah.
After I determined that was a good way to go, I was, faced with the immediate challenge of "how does one move around a one ton battery?". I had already built my solar utility room and you can't just get a buddy to help you move a > 1 ton battery through a 36" door! I considered building a battery shed, but that would have fouled up the proximity to the inverter/CCs. So... I did some sleuthing and found that it was possible to get them with breakable bars.
So this 2200 lbs can be moved around in 14 pieces (2 cases and 12 cells). I did NOT know until it arrived that it was actually two 6-cell units that could be independently moved (1100 lbs each) - which did help with unloading, because that is in the range of what my FEL can lift. It also came with a tool to bolt on to each cell's terminals that allows one to life them out with a pipe or hoist, etc. Each cell is in the 160 lb range, the cases are about 100 lb maybe? It is very manageable with a helper. So we moved it as close to the room as possible (with an FEL), then carefully removed each cell, moved inside, and re-assembled. Not something I'd want to do every year, but every 5-10 years... that isn't bad.
Ok, so let me ask a question related to the 80% DoD... Because I have a battery backup system, I exercise it every couple of weeks by shutting down my main power for at least 24h. These batteries are otherwise not very happy to just sit there at a float charge. I have the Schneider BTS (Battery Monitor) and last week while running on battery power, it was showing my SoC to be like 64%, but the voltage to be 25.1 or so. I know that the only real way to check the SoC is to use a hydrometer, but it was 3am, and I was not about to go out in a sleep stupor and check 12 cells with a hydrometer
I have SoC triggers set on my AGS (generator) module, and so it kicks the generator on if the voltage reaches a defined limit. This seemed pretty low to me for voltage, so I set my trigger so that it would turn the genny on if the voltage remained at 25.1 for 15 minutes. I did kick it on.
I want to discharge to 80% DoD every now and again, but I would expect the voltage to be higher for much longer and much higher for that Soc% percentage. At that time, I was probably pulling an average of ~33-40 Amps continuous. That should be just fine a discharge rate on this battery, no?
So I'm just trying to understand how much I should pay attention to voltage with the BTS, and how I can discharge the batteries to 80% DoD (Not normally - but every so often. I usually keep it set to 50%, because diesel is cheaper than batteries). I'm puzzled why the BTS equates that SoC with that voltage. Is there any guidance or general info that roughly equates the voltage to SoC? Make sense?Comment
-
OK they are GB Batteries. GSI threw me off the trail. As for the weight it is hard to tell from the pics, but most all industrial batteries like that, you can remove each individual 2-Volt Cell So instead of moving a 1100 lb 6-cell unit, each cell should be around 170 lbs you can remove from the case.
Resist discharging to 80%, limit it too 50%. Just because you can discharge them to 80% does not mean you should. Nor wold I exercise them frequently unless the manual says otherwise. Remember batteries have two life cycles. One is cycles, and the other is calendar. Which ever comes first. The deeper you discharge, the fewer cycles. Fork lift operators do not worry about DOD because as a matter of replacement policy cycle of 3 to 5 years. That is why you can buy used ones that still test 80 to 90% capacity. FWIW end of life is 80% capacity.
You mention hydrometer. Are they flooded or AGM. Fork Lift batteries tend to be VRLA and there are some FLA out there. The good news with Fork Lift batteries is they are very low internal resistance, and the SOC error under load and charge are less severe. However if these are used in Stand By, the open circuit voltage is fairly close. However you probable want to know, or at least I would what is the dangerous voltage under load you should Cut-Off. Easy Peazy, just listen up I will go over it at the end.
As for the part number of 12-125-17 is an Fork Lift generic standard for voltage (12) and Form Factor (125-17)
OK you need a way to measure battery load current, and a way to vary the load on the batteries. You will do this with no charger what so ever connected. You want the battery SOC from voltage to be around the 50 to 70% range to begin the test. You are going to be testing to Find Delta Voltage aka Dv, and Delta Current aka Di. Don't sweat the name, it is easy. We are going to find the Internal resistance of the battery when it is new 50% DOD. This number you will find very useful in the future to determine battery health.
So here is what you do.
1. Get the batteries discharged to 50 to 70%. and let them rest so they are not hot and at normal temps. Apply a light load say 5 to 10 amps. Measure the voltage under load directly on the battery Term Post. Record voltage, call it V1, and the Current C1. Example V1 = 25, C1 = 5 amps. Be as accurate as you can down to 4.5 digits or more. like 25.012 and 4.981.
2. Repeat same test except this time load the batteries as much as you can say 100 amps and record th evoltage and Current as above except call them V2 and C2. Example 24.752 and 101.2.
3. Time for easy peasy math.
Find Dv = D1 - D2. In our example 25.012 -24.752 = 0.26 volts
Find Di = I2 - I1. In our example 101.2 - 4.981 = 96.219 amps = Di
Find Battery Internal Resistance = Dv / Di. In our example .26 / 96.219 = .0027 Ohms Record this number and save it with date.
So here is what you do with that info.
1. Determine Low Voltage Cut-off under load. Determine what current you think might be your maximum load current say 50 amps. Find the voltage sag (IR) = Ri (Internal Resistance) x Load Current. In this example 50 amps x .0027 Ohms = 0.135 volts.
2. Determine what SOC% voltage you want to Cut-off at. Let's pretend and say 20% SOC or 80% DOD = 24 volts Open Circuit Voltage. Your cut-off voltage is 24 volts - (IR). In this example 24 volts - .135 volts = 23.9 is close enough. Done.
Th eother way to use Ri is battery health. Over time the Ri will increase as the battery ages and wears. When it raises 50%, you are at end of life.MSEE, PEComment
-
Thanks a lot Sunking - I will do this test as soon as I am able.
FWIW, a couple months ago, I had come across this info in my inverter docs: " For XW system, the battery is regulated according to Low Battery Cut Off (LBCO). Therefore, it is important to understand that the Battery Voltage at 60-65% SOC shall be equivalent to LBCO +2V. Ensure that this defined Low Battery Cut Off (LBCO) value does not void battery warranty.”
So I emailed my vendor, who contacted BBI with the request for info. They responded with: "The parameters for the setting would be 1.66-1.70 volts per cell."
What is my point? I suppose just that this gives me an idea what the vendor feels is appropriate voltage for a certain SoC.
Comment
-
Sunking - forgot to mention... the batteries are FLA, not VRLA. The manufacturer specifically instructed to discharge to 80% DoD at least a "few times a year". I wouldn't do as a standard practice - my hardware is set to allow up to 50% DoD. I'll be doing the test your prescribed as soon as I am able.Comment
Comment