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offgrid ![]() Senior Member ![]() Joined: 23 Jul 2018 Online Status: Offline Posts: 1850 |
![]() ![]() ![]() ![]() Posted: 13 Nov 2019 at 4:15am |
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Actually Li batteries are less finicky to charge and maintain than PbA’s. You can leave them at partial state of charge for long periods without damage. You don’t need a complex multistage charger. Just a simple max cutoff voltage is fine. No trickle charging needed. No water adding.
There are a couple of don’ts with Li. Do not overcharge, ever. Do not use them at cold temps. Warm them up first. Don’t discharge them 100% (that applies to PbA’s as well of course). So they aren’t harder to manage, just different. As for cost to convert from PbA to Li, the batteries themselves are close enough in cost now that you break even or come out ahead if you boondock and keep your trailer long enough to benefit from the much longer cycle life of the Li batteries. But all your charge control equipment needs to get changed too (a/c charger, tow vehicle charging, and solar). That significantly changes the cost equation. Re energy vs power, let’s keep our measurement units straight. Amperes are units of electric current. Volts are units of electric potential. Volts x amps = watts which are units of power. Energy is power x time = watt hours. So watts = volts x amps x time. Batteries are energy storage devices. But they are generally rated in terms of how long they can provide a given amount of current while being discharged. That is amp hours = amps x time. The reason for using amp hours and not watt hours is because the voltage delivered by the battery changes during discharge. So for our purposes it’s easier and more accurate to use amp hours to compare different batteries as long as you are comparing two nominal 12V batteries. |
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2015 Rpod 179
2012 Toyota Highlander |
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Olddawgsrule ![]() Senior Member ![]() Joined: 20 Sep 2017 Location: New Hampshire Online Status: Offline Posts: 588 |
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Well, now I have a clue as to what you were implying. I agree with Glue on this.. Wattage is 'power' and watt hours is power over a period of time.
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Olddawgsrule ![]() Senior Member ![]() Joined: 20 Sep 2017 Location: New Hampshire Online Status: Offline Posts: 588 |
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Again, thank you and well said. I deal in wattage mainly to track what is used and what is replaced. Dis-charge/charge cycle. My meters track this for me as watt-hours. I would be close if I tracked amps, yet as you say, wattage changes according to solar in voltage and battery out voltage. Much prefer tracking with wattage. Also much easier in a power audit when you have both AC & DC appliances.
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GlueGuy ![]() Senior Member ![]() ![]() Joined: 15 May 2017 Location: N. California Online Status: Offline Posts: 1918 |
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... and I still prefer using watts. Precisely because amps will vary by voltage. Unless the load is purely resistive, the amps will go up as the voltage goes down. This is particularly noticeable with lead-acid batteries because their voltage changes with their state of charge.
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2017 R-Pod 179 Hood River 2015 Ford F150 SuperCrew 4WD 3.5L Ecoboost |
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offgrid ![]() Senior Member ![]() Joined: 23 Jul 2018 Online Status: Offline Posts: 1850 |
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Thanks for the correction. ![]() Which loads are constant power (current goes up as voltage goes down)? LED's aren't, water pumps aren't, fans aren't. Those are the main 12V loads in the trailer. The reason for working in amp hours is that it makes load calcs, battery sizing, and solar sizing easier, not that you can't do it either way. That's how the off grid solar industry does it and why. If you want to work in watt hours that's fine too, you just have to be careful to apply the correct conversion factors for battery round trip, charger, and solar array efficiencies. No need for a debate about it I don't think.
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2015 Rpod 179
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jato ![]() Senior Member ![]() ![]() Joined: 23 Feb 2012 Location: Kewadin, MI Online Status: Offline Posts: 1817 |
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There are a couple of don’ts with Li. Do not overcharge, ever. Do not
use them at cold temps. Warm them up first. Don’t discharge them 100%
(that applies to PbA’s as well of course). posted by OFFGRID Here I sit with my pair of nearly 9 year old 12v Interstate group size 24 deep cycles, considering the Lithium until I read the above post by Offgrid. So . . . . do not use them at cold temps. Hmmm, for the majority of the time we have camped with our 177 over the past nearly 9 years the bulk has been in the shoulder months (when it is colder) and where electricity is not available. So if and when these give up the ghost it looks like I will go back the the LA style, but maybe look at a pair of golf cart batteries instead. For the most part we change out each battery when it gets to 12.2 volts, hence that may be part of the reason they have lasted as long as they have. Also regular cleaning on top with baking soda and keeping an eye on the water levels. Being in the golf industry for over 40 years I have found it interesting how Yamaha, about 6+ years ago went to the 48 volt system. No, they do not use 4 12v batteries but 6 8v batteries. Hopefully there will be enough demand for the 6v ones (like the old 36v electric carts had) so that they don't become discontinued.
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God's pod
'11 model 177 '11 Ford F-150 Jim and Diane by beautiful Torch Lake "...and you will know the Truth and the Truth will set you free." |
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offgrid ![]() Senior Member ![]() Joined: 23 Jul 2018 Online Status: Offline Posts: 1850 |
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Keeping a Li battery warm shouldn't really be a show stopper if you would otherwise want to make the switch from PbA. In an rPod I would suggest placing the Li battery inside the heated part of the trailer somewhere. Since they don't outgas or need easy access for adding water that would be fine and the battery wouldn't be subject to extreme temperatures that way.
That being said if there is no other compelling reason to make the change (reducing weight and or increasing capacity) then sticking with PbA and all your existing charging gear makes economic sense. The 6V configuration is common in the RV and off grid solar world too so I think there's not much worry it will get discontinued anytime soon.
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2015 Rpod 179
2012 Toyota Highlander |
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Olddawgsrule ![]() Senior Member ![]() Joined: 20 Sep 2017 Location: New Hampshire Online Status: Offline Posts: 588 |
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Well, you don't wish to over-charge a Pba either.. that's called boiling the battery. Li is more sensitive to cold where Pba is to heat. Both batteries types survive best at room temp, 68F or 20C. It is stated that every 8C or 46F increase you cut the life of the Pba in half (I assume same is true with decrease). Lithium now has the advantage in warm weather climates. It is also stated that a Pba will loose capacity in colder weather. Stated that at 32F or 0C you've lost 15% of your battery capacity. If your camping at 0F or 18C you've lost almost a 3rd of your battery capacity Neither really likes cold weather. The additional benefit to Li is it 'can' come into the living space and operate normally with no hazard. Again, it can come into the house and operate there as a UPS or Backup power. Going Li is a choice to be made by ourselves and our own intentions. What works for me, may not for you. My hesitance was multiple: Cost being #1, verifying my power audit as to how we camp & what we actually use and finally weight. For me, it now makes sense.
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offgrid ![]() Senior Member ![]() Joined: 23 Jul 2018 Online Status: Offline Posts: 1850 |
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2015 Rpod 179
2012 Toyota Highlander |
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