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Old 11-23-2020, 12:31 PM   #21
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charge rate

I think it was the OP who mentioned the goal of keeping the batteries charged. Lithium batteries will last longer if you charge them well below capacity most of the time. i.e. There's no problem charing them to full capacity when needed, but if you are idle, at home, don't need a full charge, only charge them 50-70%. The BMS will typically work to spread the charge around the cells and the overall system will last longer.

This is true for all Li batteries. It's what Tesla recommends. Apple has now built it into their OS's to only charge the battery to 80% automatically, or for phones to charge to 80% and then only to full just before you wake up so the battery spends a little time as possible at 100% charge
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Old 11-23-2020, 07:03 PM   #22
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Look into grey and black water heating pads in the rv space. WOrk great. It's what ive used. They kick on automatically at around 45f.
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Old 12-02-2020, 07:04 AM   #23
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Anyone see issues with using the Facon heating pads on an AGM battery setup? Also looking at this heater wrap for when its parked at the house (so I don't use battery power- easy to plug in) Northern Michigan winters get COLD!

Linkhttps://www.amazon.com/iPower-Hydrop.../dp/B01IDQD32Y
(Note- if you google it- there are less costly options vs amazon- the links were just super long to post in here)


Thanks!
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Old 12-02-2020, 02:16 PM   #24
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I bought but haven't installed one of these small heaters:

https://www.amazon.com/dp/B07B26KKH7/

On a bench power supply it only pulls ~60W and not the advertised 100W, which I think is about perfect for my intended use. My plan was to place the battery within an enclosure that is only slightly larger than my battery (think: repurposed insulated semi-rigid cooler bag) and recirculate the air. My EMUS BMS is configurable to control the heater and charging bus disconnect based on battery temperature. The discharge bus disconnect is separately configurable, so the heater will run off the house battery.

I haven't installed the heater yet because in practice it hasn't been an issue for my use case. If I'm in the van and/or out using it, it's generally going to be at a warm temperature; and if it's not, I'm not discharging the battery so I don't care that it's not able to charge. Really the only corner case I'd be looking to cover is to prevent the system from entirely disconnecting the battery when it gets too cold, since I'm powering the BMS from the house battery. For now it's easy enough to just go out and turn on the Webasto heater full-blast for 20min on super cold nights, which serves the dual purpose of "blowing out the cobwebs" to keep the heater in good running condition. So far, even on nights in the 10s (deg F) without running the heater, I've only had the charge bus disconnect, not the discharge.
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Old 12-09-2020, 07:01 PM   #25
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Time to report back. I have installed the SoliStat thermostat and the heater, and they are working as expected. I built an insulated enclosure around the batteries, so there is not a lot of space to heat. I got the Solistat2 with 20 amp capacity and configured to turn on at 35 and off at 40 - see https://www.oemheaters.com/category/...dc-thermostats - (I only needed the 10 amp model, but they happened to have the 20 amp from a cancelled order and sold it for the price of the 10 amp at $90.25.)

The heater is a 60W 'compact enclosure fan heater' - see https://www.omega.com/en-us/industri...ers/p/FCH-FGC1. This was $169.58 including shipping. During use it is drawing a little under 5 amps at 13.25 volts.

These are quality components designed and built for industrial use, so I expect they will be able to handle the rigors of travel. They were expensive, but many of the other options in this thread are equally or more expensive, so I don’t feel too bad about that. And now I don’t need to worry about my batteries being damaged by charging below zero. During testing all seemed to work fine. The time taken from the heater turning on to getting above 40 degrees and turning off took about 10 minutes.


However, given some of the information provided by contributors to this thread, I’m wondering if I needed to do this. My goal was to just leave the solar charging ‘switched on’ all the time to keep the batteries fully charged, and not have to worry about it charging frozen batteries. But the information about not keeping Lithium batteries fully charged has changed my thinking. It would be easier to just turn off the solar and let the batteries discharge for a while, before recharging. I did some research based on the information provided and it does appear that it’s best not to keep the batteries fully charged, and also to reduce the number of charge cycles. Apparently the LiFePO4 batteries are less affected by keeping them at full charge, but it is still recommended not to. So a practice of perhaps letting them discharge for 10 to 20 days (or more) and then recharging would seem to be the best option. In which case I could leave the solar off except during the now infrequent charging cycles – which would only be performed when temperatures are warm enough. In fact, as I rarely leave the van unused for more than a couple of weeks, just driving it would keep the batteries charged. Interestingly the SportsMobile manual recommends staying attached to shore power at all times while inactive if possible – it says the batteries cannot be overcharged. But that is applicable to AGM batteries and it appears SportsMobile are still catching up with the realities of Lithium.

Attached some photos. The first shows the overall setup, with the thermostat on the right and the heater on the left. Then a close up of each. I am pleased with how its working, even if I now don’t think I need it.




Attached Thumbnails
IMG_0519 - Medium.jpg   IMG_0517 - Medium.jpg   IMG_0518 - Medium.jpg  
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Old 12-09-2020, 09:09 PM   #26
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Nice solution. The fact that the components are so small, even better. Since I live in Phoenix, I’m not going to have to worry too many nights (only 14 days/year that temperature drops below 40 degrees F). Since my van is parked in my driveway, and I have access to 110 V power source, I chose to go with a small ceramic heater in the garage beneath the platform bed, where the batteries are stored (Lasko ceramic MyHeat $28.00 Amazon).
The temperature dropped below 40 the other morning and I took a picture for “Proof of Concept.” Indoor temp is on the top
I also purchased a Moat S2 Wireless Temperature & Humidity Bluetooth Smart Sensor (2-Pack) to monitor the temps inside/outside the van, remotely.
My battery terminal temperature at the time was 62.6 F (17 C). I used a simple plug in timer to turn the heater on/off based on the hourly forecasted temperatures.
Not as elegant as PhilH’s setup but it looks like it will work for me. If the van was kept in a more extreme environment, I would go PhilH’s route, for sure.
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9691DB69-1EDE-42B4-9DAB-1C45018D8102.jpg   AE6E716E-A3FB-40B9-85B6-0A815651838E.jpg  
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Old 12-13-2020, 01:09 PM   #27
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That Moat sensor looks like a really good idea. I think I'll get one so I can keep track of how everything is working. It will also be interesting to see how effective the insulated box is.
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Old 12-13-2020, 03:07 PM   #28
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There is a lot of good info on Lithium Iron Phospate, etc. battery heating, conditioning and life.
Here is a read on thermal protection

https://diysolarforum.com/threads/li...emperatures.5/


On Li chemistry life this is worth reading thru, look at table 4 if time is short
https://batteryuniversity.com/learn/...ased_batteries


The diysolarforum is interesting as many are rolling their own....(if you have the time or inclination)

Cheers,
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Old 12-13-2020, 07:47 PM   #29
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Quote:
Originally Posted by moorefc View Post
On Li chemistry life this is worth reading thru, look at table 4 if time is short
https://batteryuniversity.com/learn/...ased_batteries
Be careful drawing conclusions about LiFePO4 batteries when reading articles that broadly refer to "Li-Ion", as Lithium Iron Phosphate behaves significantly differently than "typical" Li-Ion technologies such as cobalt-based.

Specifically, the referenced article states:

Quote:
The following tables indicate stress related capacity losses on cobalt-based lithium-ion. The voltages of lithium iron phosphate and lithium titanate are lower and do not apply to the voltage references given.
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Old 12-13-2020, 08:02 PM   #30
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Kibo I agree, Li chemistry has some common traits that are very different than Lead acid, AGM, etc...Voltages vary but the chemical reaction relationship to stress is similar within the family...Life cycle vs stress voltage and temperature are characteristics common to the chemistry. LiFePO4 is more stable than other Li chemistries.
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