|
Post by biggkidd on Jun 2, 2022 18:35:43 GMT -6
16 cell LiFePO4 at 56.8V is 56.8/16 = 3.55V/cell - my favorite LiFePO4 charge voltage ;-) 42 / 16 = 2.625V/cell, just above the recommended 2.5V/cell (2.0 is absolute minimum) The batteries aren't cheap but they pack a lot of power for their size. Charging voltage or charged voltage?
|
|
|
Post by papaof2 on Jun 2, 2022 19:07:08 GMT -6
Fully charged voltage - the charging voltage may be higher but the BMS will stop the charging when all the cells reach the desired "charged" voltage.
The better BMSs will have options for maximum voltage to charge up to and minimum voltage to discharge down to - usually in volts/cell as well as the pack voltage. If the BMS does balancing, it knows and maintains the per cell voltage to whatever you've specified. A BMS may do its low voltage shutoff when just ONE cell drops below the per cell minimum voltage. A BMS with an app for setting/reading parameters usually can display the per cell voltage for for all the cells in the pack. The balance parameters can usually be set to whatever voltage range you think appropriate - 10mv, 5mv or whatever the BMS offers.
I'm not surrently dealing with a BMS that sophisticated - just something to protect the cells in the pack for the UPS from being overcharged (something bottom-of-the-line UPS units are noted for) or overdischarged (same - an inexpensive UPS typically runs its AGM battery down to 10.7 volts or less before it shuts off, as it tries to get maximum run time for the devices being powered). I haven't measured what the balance voltage difference is on the small pack (the BMS is not settable) but a quick check with a calibrated voltmeter has all the cells at the smae voltage immediately after charge. I have a 3.8AH LiFePO4 pack that was charged a couple weeks ago and has been sitting unconnected since then. I should check the voltages of the cells and see if they are still equal.
|
|
|
Post by biggkidd on Jun 2, 2022 19:37:34 GMT -6
Gotcha that's what I thought you meant but better to be sure. I think I'll set my charge parameters a little different. I ordered the Renogy BT-2 today so I can set the voltages I want in the charge controller. I'm probably going to set the maximum charge around 53.6 the bottom will take care of itself. I highly doubt it ever sees below 48 volts and probably not less than 52 Going by the kWh I've been using daily. Gotta remember it's charging anytime the sun is shining, unless I'm in the woods. lol I'm going to hold off on a BMS for now since I can keep an eye on things pretty tight since I will be using this everyday. I found the BMS I want but it's kinda pricy at nearly $250.
|
|
|
Post by biggkidd on Jun 2, 2022 19:46:47 GMT -6
1.75 kWh and still holding 52 volts! Amazing
|
|
|
Post by papaof2 on Jun 2, 2022 20:13:34 GMT -6
I'd expect the voltage to hold for maybe 80% or better of the battery's capacity and then drop off rather steeply. There are a number of Youtube videos about LiFePO4 BMSs and battery testing. The LiFePO4 cells have a long, flat discharge "curve" and then they just turn the corner and go almost to zip. With a BMS for discharge protection, the first cell that drops below the acceptable discharge voltage will trigger the the BMS to shutdown. You'll need to watch your setup closely as the voltage drops because you might have a cell that's weaker than the others and it going below 2.0 volts might not be obvious but could be damaging.
Remember that LiFePO4 cells are identified as 3.2 volt cells. At 52 volts, that's 3.25 Volts/cell or in its "nominal" operating range.
I'm in favor of never taking any lithium-based cell below its minimum voltage - I've seen far too many lithium-ion laptop packs die from having every last second of use squeezed out of them. Today I've been updating a Win 10 laptop using a battery I took out of service a couple of years ago because it lasted less than 2 hours. A full charge today and I had no qualms about using it for major software installs and updates because the battery would be fine as long as needed if there was a hit on the power from the passing thunderstorms. I wrote my own Battery Monitor (works in Win 95 and up) that can be set for two levels of alert (flash the icon in the taskbar and beep until stopped) to alert me to the laptop battery's level. I usually set it to flash at 40% capacity and beep at 35% capacity. I've gotten 4 years out of some of the lowest-cost-vendor batteries by not pushing the lower limit. I think that probably applies to LiFePO4 as well but the LFP packs I've put into UPS units have the BMS low voltage shutoff at 10.0 volts (2.5V/cell) but the UPSs do low voltage shutdown at 10.7 volts (2.675V/cell) so I actually only need the BMS for charging and balancing.
|
|
|
Post by biggkidd on Jun 2, 2022 20:50:53 GMT -6
Yes that flat curve is what got me so interested. Well that and the massive amount of useable amp hours for the size & weight.
You can believe as soon as the golf cart is finished I will start saving for a set for our primary power. We might have one to two years left in these batteries we're using now.
I'll check cell balance every week for a month or so and get an idea what the system is doing and go from there.
I'm thinking things are turning that last corner before getting real bad though. Kind of feels like we crossed the point of no return . If that happens who knows what I'll do about batteries in a year or two! Just glad to have these in hand now.
|
|
|
Post by papaof2 on Jun 2, 2022 21:42:27 GMT -6
I built a spreadsheet with all the things we might want power for, how much power is needed for that device in 8 hours, one day, one week. If we lost grid power for an extended period (month or more), I'd be going down that spreadsheet and saying "This we can have. This we can't have. This we can have in the summer only" (5 hours/day useful sun vs 3 hours/day useful sun in winter). If the grid is down (even over just an area of a few square miles), there's the possibility of no phones (cell or landline - telco offices and cell towers have some backup power but not probably not more than 2 weeks; a few cell towers may be solar-charged but they still need a connection to a telco office to get to the backbone network). If you have Uverse or FIOS, their remote terminals need power and my knowledge of Uverse is that they have NO backup - apparently they assume that if the power is off in the area, the customers won't know that Uverse or FIOS isn't there because the customers have no power either. Sorry, but when our power was out for 12 hours, Uverse was out for 30 hours so that logic is flawed. However, that idenitifies equipment that won't need backup power: Uverse/FIOS router, cordless phones, DVR, cable boxes, internet hardware. The solar backup system isn't big enough to run the fridge, freezer and furnace blower or a small window A/C so in winter some fridge/freezer things might go in coolers and be put on the screened porch to be kept cool. There would be power for the 4.4 cu ft counter height fridge, so we'd have a little bit of refrigeration winter and summer - just need to "eat down" what's in the freezer to an amount that could be moved to the fridge's freezer section. That would be easier in winter because of the natural refrigeration some months. If County Water stayed up, we'd have running water. If the natural gas lines stayed up, we'd have easy hot water and heat (otherwise two fireplaces and probably running a gen to cut and weld a couple of 20lb propane tanks into small stoves that would fit in the fireplaces - more efficient than an open fire and I could have a battery-powered fan moving air around that stove to warm more of the room.
I have a two page document on the what and how of water (30 year records have enough water for the two of us all year from one downspout and there's another downspout that could be added to the IBC tote and 55 gallon barrel collection system to double that collection). If I had above-freezing space for a 5000 gallon tank, it would be filled the first year and I have the filters to make that water potable and a page on how all that would be connected and the small DC pumps powered from the solar battery bank. If I had 5000 gallons of water, I could rig a warm shower at least once a week ;-) Right now, I have 300+ gallons of potential rainwater storage and a 150 gallon tank that would be the holding tank for clean water, with that water pumped on demand to the kitchen sink and the master bath. All that plumbing isn't in place but I could get it in place in a few days and then just double the Rx pain meds so I could sleep :-( I've done research on the Rx pain med and that's a reasonable way to handle a few days of much greater than normal effort (and its associated pain). Good to have battery powered tools and clean power to recharge them, but I also have a lot of hand-powered tools to fall back on ;-) There's also a Number 2 wash tub and a clothes washing dasher from lehmans.com - no, I haven't yet sprung for the $175 hand-cranked wringer from Amazon or the more expensive one from lehmans.com.
If power was out a week or so, I'd be using portable lights - even the solar-charged walkway lights, some oil lamps and lanterns and a candle lantern - the fact I can have bright steady light doesn't mean that I should let the neighbors know about it...
|
|
|
Post by biggkidd on Jun 2, 2022 21:52:38 GMT -6
You have the bases well covered!
2.25kWh used voltage at 51.5 simply amazing.
|
|
|
Post by papaof2 on Jun 2, 2022 22:42:49 GMT -6
51.5 volts = 3.21875 volts/cell
2250WH / an average of 52 volts translates to 43.27AH plus whatever the efficiency of the inverter is (maybe 85% ?) so 43.27 / 0.85 = 50.9AH or approaching half the battery's AH capacity. However long you've been running the test, you probably don't want to run more than 60% of that much time on this leg of the testing so you don't drop below 20% DOD. Or just run it for 60% of the WH or maybe another 1.35kwH to have a not-fully-discharged-battery.
I do this type testing but with a 200 amp shunt feeding a volts/amps/watts/AH/WH meter so the losses through the inverter are taken into account and I can directly read the AH taken from the battery. Maybe $40 from banggood.com or aliexpress.com
|
|
|
Post by biggkidd on Jun 3, 2022 7:54:09 GMT -6
I've got all the shunt meters on the cart. Ended up running a total of 3.146 kWh, voltage was at 47.9 this morning. I'm happy with that considering it didn't have a full charge. I left the AC on most of the night. It's thermostat controlled.
|
|
|
Post by papaof2 on Jun 3, 2022 13:45:13 GMT -6
3146WH /50V = 62.9AH plus the inverter efficiency (85%) 62.9 / 0.85 = 74AH
Not bad for "not fully charged". "Fully charged" can take a while, as the cells need to sit at the desired "fully charged" voltage for an extended period to absorb that full charge. A cell being at 3.55V doesn't mean it's fu;ly charged - it may need to spend several hours at that voltage to actually be "fully charged". The best way to manually determine when a battery is fully charged is to detect when the charge current drops to 5% or less of the initial charge current. For a 20 amp charge current, that would be 20 * 0.05 = 1 amp.
|
|
|
Post by biggkidd on Jun 3, 2022 20:16:12 GMT -6
I'm pretty much only using a 5 amp charge. I can rig up the 18-20 amp charger to do it but there's no need. The way I'm designing the system is to just sort of hover anywhere in the middle range. There's a chance I might have to either use a second panel or plug in on successive cloudy days but I hope not. Thankfully the days the sun doesn't shine I'm not as likely to be as busy. But even without sun with my normal use I should be able to go 4 days without issue. Hopefully those days will still make enough charge to let it go indefinitely with my limited use.
|
|
|
Post by papaof2 on Jun 3, 2022 20:24:08 GMT -6
Be sure to keep a log: 3 June - sunny, charged xx AH
4 June - cloudy, used yy AH
5 June - cloudy, used zz AH
6 June - sunny, charged aa AH
You'd need to keep that log for at least a year to know what to expect each month but you would have a good feel for "Two cloudy days starting tomorrow but should be OK for the usual running around because yesterday was sunny."
|
|
|
Post by biggkidd on Jun 4, 2022 5:23:10 GMT -6
I think the voltage will pretty much tell me what I need to know. I'm really bad at keeping records of any kind. A lot of the problem is I have a real hard time writing. M.S. pretty much stole that ability.
|
|
|
Post by biggkidd on Jun 4, 2022 19:43:03 GMT -6
My daughter and son in law wanted to know if the golf cart was any quicker than it was at first. This is with lead acid 48 volt bank versus the 36 volt bank it had originally. So I romped on it with Nate and Tj (grandson) and I in the front Kyrstin was on the rear seat. The dang thing pulled about a 6 inch wheelie! Nate and I were both like naw that didn't happen so I did it twice more it happened twice more, in fact it did happen all three times. I will say two things 1) these batteries seem to be getting better with everyday of long slow charging 2) battery voltage at the time was about 53.5 volts. With the panel charging. I can't wait to see what it will do with the new battery!
|
|
|
Post by biggkidd on Jun 5, 2022 18:13:35 GMT -6
Started building the battery box today. It's 10.5W x 12L x 12T. Still a long ways to go. Trying to make it breathable for summer yet sealable for winter is not that easy. The worst part is I had to resort to using steel. I tried every which way to come up with enough aluminum but I just wasn't able to make it happen. I repurposed an old metal shelf to make it out of. It may not look the best but it will work.
|
|
|
Post by papaof2 on Jun 5, 2022 18:45:57 GMT -6
If it works and it lasts at least a year, it's good - because you'll have more ideas for changes by then ;-)
|
|
|
Post by biggkidd on Jun 5, 2022 19:34:06 GMT -6
If it works and it lasts at least a year, it's good - because you'll have more ideas for changes by then ;-) Please NO! I want to do this part ONCE only and I want it to last at least 20 years. Now who knows I might be persuaded to add another battery in parallel. I think I have one more of these shelf pieces to make a matched pair. lol
|
|
|
Post by papaof2 on Jun 5, 2022 21:54:53 GMT -6
Already adding another battery and knowing where the needed parts are - my words confirned!
|
|
|
Post by biggkidd on Jun 6, 2022 15:07:17 GMT -6
Ahh ya never know but I hope and pray this single battery will do everything I need it to!
Been out working on the battery box some more. Just finished testing the heating and cooling system for it. Never thought I'd see the day when I'd be temperature controlling a battery! Got a pair of 25 watt heat pads under an aluminum sheet over Styrofoam that the batteries will sit on. Also have a 4 inch fan 1.44 watts to go on the top drawing air from the bottom up around the battery. If I end up getting a BMS then the fan will probably be replaced by it since it has it's own fan. I have the fan coming on at 35c and off at 30c the heat will come on at 3c and off at 5c. Why in the world can't this stuff be in F and not C?
Still debating where I should place the battery. Either in the middle or on the passenger side? Both have pluses and minuses. Any opinions?
|
|
|
Post by papaof2 on Jun 6, 2022 17:24:20 GMT -6
In the middle to balance the load if you mostly have two passengers. On the passenger side if you mostly travel alone. Does the cart suspension need any changes with the removal of a couple hundred pounds of batteries? Maybe the headlights need to be re-aimed? The large portion of the world that uses degrees C has never landed a man on the moon and successfully returned him. The minority, that uses degrees F, has done that. It's not a better system, but as the French think they need to keep their language "pure" the rest of the world blindly follows their lead in the not-very-accurate metric system. The original "meter" was based on an inaccurate estimate of the Earth's circumference so their measurement basis is no better than the "yard" which was based on the distance from an English king's nose to the end of his fingers: en.wikipedia.org/wiki/Yard#Henry_I (also said the be the Welsh "pace" of roughly three feet, and eventually the British Parliament's legislation about "brass tacks" for measuring yard goods - because the inspector could easily compare that spacing to the governmentally decreed length of a yard, based on the official rod he carried. The larger market is the majority of the Chinese vendors' customers so things read in degrees C or cm or meters. I did find ONE temperature control unit that read in degrees F when I was looking to build a controller for a Peltier (TEC) cooling device. The first semi-efficient Peltier fridge I've seen was on YouTube and had a LOT of engineering in it - including the size, shape and materials of the fridge "box" and the design and placement of the heatsinks. If I had a need for DC fridge, I could copy that design. However, I don't think it beats the Engel compressor fridge/freezers by much - other than being a vertical door fridge instead of a horizontal lid cooler. I did some testing with a well insulated box (small polystyrene cooler inside a larger polystyrene cooler for two 2" layers of poly separated by 2" of air and the inner cooler being cooled by a single 60 watt Peltier on a heatsink with fans on both sides (big fan taking away heat, small fan stirring up the cool air) and found that one problem is that the thermostats turn off power to the entire Peltier unit when they should only turn off power to the Peltier chip and the cold side fan for 5-10 minutes so the Peltier and its heatsink are cooled down by the ambient air flow and the heat left in both of those is not passed to the cool side by the thermal conductivity of the Peltier chip itself - and then turn the hot side fan off. In most of the available chip + heatsink designs I've seen, the heatsink needs to be twice as big and with twice as much air flow for taking away the heat.
|
|
|
Post by biggkidd on Jun 6, 2022 20:09:12 GMT -6
No worries on suspension changes it'll gain some of the weight back in accessories and additions. All the same stuff I would have done regardless of battery weight. I'm sort of thinking of adding a small 12 volt battery to run a winch. But then I'd need a stepdown charger to share power with the main battery. Or charge it separately anytime it's been used. Unless I could somehow wire it to charge from the 30 amp 12 volt power supply I just bought. www.amazon.com/dp/B07GPZWG1S?psc=1&ref=ppx_yo2ov_dt_b_product_detailsActually used more watt hours than it made today by about one hundred. Then again I was running here and there getting pieces parts to work with.
|
|
|
Post by papaof2 on Jun 6, 2022 21:35:08 GMT -6
Check the manual on the winch you may be thinking about. Even the "small" BadLands 61297 2500lb ATV winch from Harbor Freight (used to be $50 on sale) needs a LOT of power. Example, from the manual: Battery 12VDC, Minimum 12 Ah Battery Cables 10 gauge, 5.8′ (1.78m) long (THHN 90 degree C wire is rated for a max of 40 amps. You may get away with a bit more with VERY short leade and very short winch pulls.) The first layer of wire (fully extended 50' cable) has the greatest pulling power and the amp draw is like this: Line Pull lb. (kg.) Line Speed fpm (mpm) Amp Draw (@ 12V) . . . . . 0 . (0) . . . . . .13.3 (4.1). 10 - 12AH battery can do this for a short while . . . . 1000 (454) . . . . . . 8.3 (2.5). 55 - 12AH battery can do this for a matter of seconds . . . . 2000 (907) . . . . . . 4.1 (1.2) 106 - 12AH battery not likely to do this . . . . 2500 (1134). . . . . . 2.7 (0.8) 132 - or this. If you need to move over 1000lbs, you need at least a Group 24 vehicle battery and check what its cold cranking amps are. Definition: The starting battery test for the Cold Cranking Amps often used by battery manufacturers is based on the SAE J537 Jun 1994 American Standard. This test measures the output amp of a 12V battery for 30 seconds while maintaining 7.2V at 0°F (-18°C). The question is how low can the voltage go and the winch still work? It has a remote control so what is the minimum voltage for the reciever on the winch to still work? There's at least one YouTube video on adding a "local" (wired) switch to that winch. That should make it work at lower voltages than when using the remote. Some of the small (walk behind) gas lawnmowers have electric start, as do many generators. The specs for the batteries they use probably give the cranking amps (CA or MCA - the power at 32F (0C)) and that might help you choose a 12 volt battery. Or you can build your own, based on the 30 second current available from LiFePO4 cells. I have some 3.8AH cells that are rated for 12 amps continuous or 28 amps for 30 seconds. That sounds very much like winch use if the LiFePO4 cells are maybe 20AH and can do 100 amps for 30 seconds - something you need to check the specs on and then you'd be buying a BMS based on the maximum winch load (up to 132 amps) I made a spreadsheet for the power that would be needed to keep a 65AH lead-acid battery charged so it could deliver 35 amps for a maximum of 18 minutes (pulling the 42" mower that's 50 feet away to and then up a short ramp and into the shed if the mower isn't running - amp draw is based on the mower's weight and the estimated "rolling load"). That 18 minutes would use a minimum of 10.5AH - a "small" battery will be dead after a few uses. That HF ATV winch also only has a 5% duty cycle at 2500lbs: 45 seconds on then 14 minutes and 15 seconds of rest. If pulling 1000lbs, assume the duty cycle is 2.5 times that or 1 minute and 52 seconds, although it might be a bit longer because the motor on the winch can probably dissipate the lower wattage a little faster or maybe you just add a radiator fan with some ducting to cool the winch and another battery to power that fan... If you buy a high-end AGM battery - the kind used in BIG backup power installations - you can get those high amps for several minutes from a relatively small (58AH) battery. Example: www.power-sonic.com/wp-content/uploads/2018/12/PHR-12200%20technical%20specifications_US.pdfThe PowerSonic PHR12200 is a High Rate battery and it can provide 111 amps (or more) for 5 minutes but it's $120 + shipping and up. That almost puts you in the market for a 12 volt LiFePO4 battery pack because it will last longer ;-)
|
|
|
Post by biggkidd on Jun 7, 2022 6:42:55 GMT -6
|
|
|
Post by papaof2 on Jun 7, 2022 16:54:21 GMT -6
Headways in 4s2p might work, depending on how mouch load amd for how long. That's a power thing - watt hours (WH) being volts * amps * time. You need to know the minimum volts required (How low can the battery go and still run the winch?) maximum amps (How much current does the winch need for that load?) and the time (How many pulling minutes and how much time waiting for the winch to cool down enough to try again?) The amount of load depends on whther your're moving a sled loaded with logs (dead weight plus sled-to-ground friction) or a wheeled vehicle (wagon or powered vehicle in neutral and brakes off). My load estimates for winching the riding mower are with the transmission release (pull tab on the back of the transaxle) in the "push me" position. Remember that some golf carts put the brakes on when you take your foot off the pedal - that could be a problem when trying to get the cart unstuck as the cart would then be similar to the sled loaded with logs and you'd be dragging dead weight on "runners" :-( Here's a reference for calculating the "drag" load: www.engineeringtoolbox.com/friction-coefficients-d_778.html
|
|