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ICC
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# Posted: 4 Oct 2019 05:58pm
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If you have a shurflo water pump use that as a test device. Mine operates fine even when the battery is being charged and the voltmeter indicates 14+ volts. It should be totally safe to try it off the Valence which is reading 13 or so. The DC system in my RV is always reading 13.5 or thereabouts when sitting outside in the sun (roof is covered with panels) Nothing rated for 12 VDC has ever had a problem with that.
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paulz
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# Posted: 5 Oct 2019 10:35am - Edited by: paulz
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Seems to be working fine now. It goes down to 13.1 when I run the Shurflo. Wifi router is fine, don't know what caused that. I forget how low I can safely run down, 12.2? Green light has never stopped blinking. I've read that when it goes yellow it means charge it.
Have to go back to dreaded city life on Sunday, going to pick up a friend's 14.4v tool charger and try that. If I can get it up to the low 14v range I'll stop and take it back to the cabin Tuesday for more testing.
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ICC
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# Posted: 5 Oct 2019 11:01am
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ICC
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# Posted: 5 Oct 2019 12:22pm - Edited by: ICC
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Something like this is what you need long term if you do not have solar for charging. However, you'd still be without an active BMS. It is an option, though. It's 1/10 of a volt under the max listed by Valence, but the 3.55 per cell provides 95% full and preserves cell life.
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ICC
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# Posted: 5 Oct 2019 02:40pm
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Or if you don't mind buying direct from China something like this one or this one. (I've never bought from either of these sellers, but have bought through aliexpress a fair amount. I also have not checked out the specs carefully, nor researched reviews, if any. Just pointing out some sources.)
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paulz
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# Posted: 6 Oct 2019 03:20pm
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Those look like what I need, thanks.
I have a couple of tool battery chargers here but they both say 7.2-24 volts. Apparently these things can detect what battery they are charging, or something. They have 3 prongs on the DC side and show somewhere around 50 volts when probed with a DVM. Not going to mess with that.
Right now I have the Valence connected to the wall wort that goes with my lithium car jump starter but it's not doing much. Sigh, looks like I'm headed back to the cabin to day at 13.2 volts again. Mighty tempted to hook it to my truck charging system..
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ICC
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# Posted: 6 Oct 2019 05:20pm
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I think the tool chargers also use a third connector for sensing battery temperature. Not sure what they do if that does not sense anything.
And yes, there are chargers that sense voltage of the cell being plugged in and then do a self-determination as to what voltage to provide. I have one for individual cylindrical cells that detects between NiMH, nicads and 2 types of lithium (3.2 or 3.6 volts)
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paulz
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# Posted: 6 Oct 2019 08:35pm
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I'm going to buy one of the chargers you mentioned next week.
Been at the cabin on the Valence this afternoon watching baseball and surfing on the Asus, 'cause I'm too pooped to work on the carport or buck wood. Down to 12.6, probably pull it soon and give it a chance with a full charge.
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paulz
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# Posted: 9 Oct 2019 11:30am
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Back to city life for a day (my cabin is only a half hour away in case I haven't mentioned it), much needed to rest from my never ending carport project. While I was looking at 14.6 chargers online I noticed two things: One they look like some 12v chargers I already have and two, they mention having a potentiometer inside to adjust voltage. Hmmm.
I take auto shop at the local jr. college, they have a class in electric cars and auto electrics (I'm in auto body) and several months ago I noticed a bunch of these batteries and chargers sitting there that had been donated. The power strip they were plugged into had been unplugged. Knowing my old batteries were dying I asked about them. They said take them. Brought them home 2-3 of the batteries hold a charge, others dead. But there are all these chargers..
Anyway when I got home last night I pulled one apart, sure enough there is an adjustable potentiometer, and with a twist it goes right up to 14.6v on the DVM.
So I am about to try one on the Valence but thought I'd check in first. These chargers have a built in cutoff, don't know how changing the output affects that but I will keep a close eye on it. They are 7 amps each, I could conceivable hook up a couple.
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NorthRick
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# Posted: 9 Oct 2019 04:21pm
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OK, so this whole post is why I'm sticking with lead for a while longer. Plug-and-play with off the shelf hardware. While I love a good challenge, I've got plenty on my plate to last me a good bit.
Hope you get it figured out Paul.
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paulz
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# Posted: 9 Oct 2019 04:54pm
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Ha, I don't blame you Rick. At least this project doesn't take much heavy labor like this year has turned out to be for me. And my lead batteries are still hanging in there, though they drop well below 12 volts after a day at the cabin they seem top come back after a day of charging.
Looks like my tweaked charger worked, I just went out there and it was at 14.6. I took it off and it has gone down to 13.4. The spec sheet says 'float voltage' is supposed to be 13.8, does that mean off the charger? Also don't know how long it's supposed to be charging at 14.6.
Back out to the cabin tomorrow for more testing.
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ICC
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# Posted: 9 Oct 2019 07:20pm
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Float voltage means the voltage the cells or batteries are kept at while connected to the charger.
LFP cells/batteries do not need to have a float charge. In fact, they may last longer if not floated and stored at just below the rated voltage.
The falling voltage after disconnection could simply mean the battery had not yet reached full charge.
FYI, a true LFP charger first runs in CC mode. CC = constant current. The voltage slowly rises. Then when the upper voltage limit is reached he charger switches into CV mode. VC = constant voltage. In CV the current into the battery slowly falls while the voltage is held constant. When the current value falls to a small amount charge is usually terminated. That current value will depend on the capacity of the battery.
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paulz
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# Posted: 9 Oct 2019 07:51pm
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Thanks ICC. You think I can put it back on at 14.6 for a couple hours? It was only there for a few minutes.
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ICC
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# Posted: 9 Oct 2019 08:58pm
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Probably but keep an eye on it.
G/L.... I may not be around for a few days... last elk hunt
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paulz
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# Posted: 10 Oct 2019 10:29am
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Charged it off and on overnight, holding steady at 13.7 now. Going to stop there. Last test at the cabin I unplugged it while showing 12.5 on the cabin meter with and amp or two load on it, and also when I unplugged it. A little while later the battery showed 13.1 stand alone.
What is a safe voltage to run it down to, under load or stand alone?
Good luck on the hunt. Had some elk sausage last summer, excellent.
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paulz
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# Posted: 11 Oct 2019 10:35am - Edited by: paulz
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So the Valence has been powering my cabin for about 15 hours now. When I plugged it in it dropped down to 13.2v fairly quickly. It's still at 13.2. This is consistent with Lifepo4 batteries, I am learning,as they keep this voltage fairly constant while in use, then quickly drop off. I plan to unplug at 12.9 volts. I could wait for the green LED to turn yellow but I have ordered the specific 20amp lifepo4 charger and will wait and give it another test with a full proper charge.
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paulz
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# Posted: 13 Oct 2019 11:59am - Edited by: paulz
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Did about 30 hours on the Valence before heading back to the city. It got down to 13.1 but was still raring to go. I'm pretty happy with the effort so far. One really nice thing about it will be the quick charging, which I can do in town a couple miles from the cabin while I work at the fire station or eat at the restaurant.
My 20 amp charger won't be here for week or two, because it's coming from SHENZHEN, GUANGDONGSHENG. Hey, the battery comes from over there too.. It is supposed to have the right charging characteristics for Lifepo4. In the mean time I am partially charging it with my 7 amp charger.
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ICC
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# Posted: 13 Oct 2019 06:59pm
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Good to hear that battery seems to be behaving itself. Lots if electronics come from the Schenzhen area. I have some meters and flashlghts on the way too.
The granddaughters each got an elk. 
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paulz
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# Posted: 19 Oct 2019 10:14am
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That's a lot of meat..
The new battery charger was waiting at the door when I got home yesterday. The LED was red on the charger when I hooked it up to the Valence, which was at 13.2. Less then an hour later the LED was green, battery measured 14.5 when first unplugged from the charger. Overnight, now it measured 13.4, or 3.35 per cell I guess. That about right, or is some of the original capacity gone?
Won't be back at the cabin until Tuesday for the big test. The question is how far down to run it voltage wise since I have no other way to gauge. Or I could wait and see if the LED on the battery goes to yellow, which I think it is supposed to without damaging the battery.
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ICC
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# Posted: 19 Oct 2019 11:52am
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Quoting: paulz The question is how far down to run it voltage wise since I have no other way to gauge.
(Voltages I use are at rest voltages.)
Personally, I would use 3 volts per cell, 12 volts for the battery, as my preferred lowest voltage.
There is no way to gauge SOC on an LFP other than voltage. Because there is not a huge working range use the best meter you can afford. Some of the cheap chinese ones are actually pretty good. If looking for a new meter consider a clamp meter if you don't have one. Sears Craftsman also has one they often have on sale for less than $40 that I like. Clamp meters allow current measurement without the need to disconnect wires. Make sure what you select works on DC current. Many less expensive ones do not. They might read DC volts but not current.
Watch the green light and the resting voltage to get an idea of when the led changes color. That will be good to know.
Quoting: paulz Overnight, now it measured 13.4, or 3.35 per cell
3.35 per cell = about 90% charge/capacity.
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paulz
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# Posted: 19 Oct 2019 04:06pm - Edited by: paulz
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Thanks ICC. I use these dime a dozen little LED meters on my trucks, tractors, motorcycles to monitor batteries. Seem to be fairly accurate enough for that. As you can see, (well maybe not from the flash) the Valence has gone down to 13.3.
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FishHog
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# Posted: 19 Oct 2019 04:36pm
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I find it really tough to use voltage as a indicator of charge level on Lithium batteries, compared to using that on Lead Acid.
Lithium tends to hold voltage pretty consistently until it drops like a rock. Kind of like when using your cordless drill. In the old days they would start to slow down as the battery got weak, now they work just great until they don't work at all.
You need to adjust your thinking from the old lead acid ways as a cheap volt meter won't provide you the detail you need to make accurate state of charge with lithium. The good news is you can discharge them much further than you ever could with lead.
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paulz
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# Posted: 20 Oct 2019 01:07pm
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Thanks Fish. But if voltage is a poor indicator, does a more accurate meter really matter? Or are you speaking of another measurement method?
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ICC
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# Posted: 21 Oct 2019 03:11pm
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Voltage is the only quick method of measuring the SOC of a lithium battery, so the accuracy of the meter is very important. Accuracy with lithium batteries is more important than with lead acid batteries where the voltage variance is greater from full to empty. Better batteries also benefit from better tools.
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ICC
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# Posted: 21 Oct 2019 03:16pm - Edited by: ICC
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I have seen some of the little voltmeters advertised as plus/minus 1% accuracy. That means that a reading of 13 volts could be anywhere from 12.87 to 13.13 volts. Round that off to one decimal place and we have probably 12.9 to 13.1. Quite a difference for a lithium battery but not as much a diff for old lead-acid.
I have several of these cheapy meters scattered about. I have checked them against my Fluke meter and they seem more or less correct but some vary by a tenth if a volt. One was off more and I tossed it.
I have owned my Fluke for years It is rated for plus/minus 0.05%. Much better than these little things. But its replacement costs more than your battery. For a lot of stuff it does not matter all that much.
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A coulomb meter can be better than using a voltage reading to determine SOC. Cost is greater. They measure energy in and energy out of the battery and are a pretty good gauge, sort of like a car gasoline gauge. Most use a shunt resistor so there is some slight energy loss. Some use a Hall sensor ring so have no need to have the shunt placed directly in a cable. The shunt also needs to be sized to the maximum expected input or discharge. Amazon, eBay, aliexpress have many. Note that many of these also are rated as plus/minus 1% accuracy as well. There are also ones made with greater accuracy with a greater price. Also note that as a battery ages the coulomb meter needs adjustment to the programmed in maximum battery capacity. Having one of those in a system is sort of like having a Kill-A-Watt measuring the whole system.
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paulz
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# Posted: 21 Oct 2019 03:43pm
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Thanks ICC. Yes I do understand the increased criticality of lithium battery voltage. I guess what is hindering me at this point is just not really knowing the lower usable range. The charger I have now does it's own charging routine so I don't need to deal with that. You mentioned 12.00 volts as a cutoff point, unloaded. so using the voltage method I need to unplug it from the cabin, where it is always under some load, and wait for it to stabilize and check voltage, then plug it back if it's above 12. Bit of a bother. Or, if the built in LED on the battery does it's job properly I could just wait until it goes yellow. It's also supposed to turn red after that and still be chargable so there must be some buffer time in the yellow zone.
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paulz
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# Posted: 24 Oct 2019 10:26am - Edited by: paulz
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Ran the cabin for 40 hours on the Valence, got down to 13.0. Had to come back to the city to get joist hangers. Put it on the 20 amp charger, went and got the hangers and had dinner, fully charged when I got back.
I ordered a programmable low voltage cutoff switch. I've been nervous that the voltage would drop off quickly into the danger zone during the night. Should fix that.
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NorthRick
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# Posted: 24 Oct 2019 01:18pm
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Quoting: paulz Ran the cabin for 40 hours on the Valence, got down to 13.0.
Any idea what load you had over that time period?
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ICC
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# Posted: 24 Oct 2019 02:20pm
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Appears to be good value.
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paulz
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# Posted: 24 Oct 2019 02:56pm
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Rick, not much load, 3 amps or so constant (wifi router, laptop and several usb chargers, 2-3 led lights at night). The shurflo water pump uses more but only runs occasionally. I have a new 12v cooler to try out, maybe even add an inverter at some point (maybe a second Valence if it tests out ok).
Back at the cabin today and plugged in but not going to go hard on it until I get that low voltage cut out.
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