lithium question

pianotuna wrote:
BFL13,

Given that SiO2 can do 4C continuously, and can be taken to 0% state of charge, why would you suggest that it takes 2 SiO2 to equal 1 LiFePo4?

because while they can go to 0 state of charge a lot more than a normal floded battery it is not a free reign to do it as it still damages the SIO2 and they can only do it so many times. the manufacturs still recomend staying in the top 50% state of charge to get the advertised cycles. I look at SIO2 as a normal battery that can take abuse if you neglect it now as one to try use like a LFP battery for cold wether. they still have lower cycles , cold weather capacity drop off and all the other issues asocialted with flooded batteries but they have a better ability to handle ocasional deep discharge to 0 and have a higher discharge capacity, but for some reason a lower charging capacity...

but I think it might take two LFP batteries to replace the discharge of the SIO2, not because the LFP cells cant handle it but because the adverage BMS is set at a 1C discharge and I dont think that will be enough for a microwave. the bonus side is with two LFP you will get 180 AH of usable power aposed to the 50-60AH from one SIO2 and you can discharge a lot more before your inverter will start giving the low voltage alarm.

Reisender wrote:
You are from BC so you know we are kinda blessed with charge infrastructure here and it’s growing super fast as well.

three years ago there were 37 charge points in Regina. Over 1/2 were free to use.

BFL13 wrote:
More idle thoughts:

You could stash the LFP and its inverter in the tow vehicle. Run the extension cord from it to the trailer shore power cord.

Note the 45 minutes won't put many AH back in even doing 50-80s.
Say you have a 60 amp charger and you are down 100AH /50%. 45 minutes will get you 45AH (minus a few for heat) so you are now at 145AH and you used 100 the first day, so by next day you are down another 100 to 45AH remaining.

Conserving to 50AH a day means you are down to 150/ 75% and where Bulk ends so your 60 amps will taper from the start doing the 75-90 so it will take longer. ( You don't do past 90 on generator on low amps and waste a lot of gen fuel for little return.) So you only are back to 180AH- restored 30AH of that 50. Next day you are down another 50 to 130AH and so on.

You could splurge the first day to get down to 50% and then do 50-90s. but in any case you will be running the gen for a couple hours a day or even longer depending, so you will need lots of propane or gasoline for it. Doesn't help if they are LFP--an AH is an AH no matter where it came from.

Having an EV for a TV you can plug into is very interesting--IMO that is the way to go if available. Nobody cares about efficiency while camping. You just want to get to tomorrow without freezing in the dark.

True. But it depends on how far your recharge point is for the EV. You are from BC so you know we are kinda blessed with charge infrastructure here and it’s growing super fast as well. But to make it worth while one would have to be camped within 30 or 40 kilometres of a fast charger. Totally possible but not a given. In that case your car is your fuel carrier. The other thing is getting the power to the RV. With something like the Ford Lightning that’s easy as it has a built in 7.2 KW inverter for operating power tools. Just plug in the RV. But for those of us towing with an EV SUV we are relegated to the 7 pin plug or small inverter and battery charger. This is super inefficient as the car has to be “on” which uses about 200 watts just for “housekeeping”. Etc.

Anyway, using the Tesla as a big battery is at best a back up plan. Leaning more to a little champion 2000 watt propane generator at this point. Probably 45 minutes to an hour of operation per day would do it.

More idle thoughts:

You could stash the LFP and its inverter in the tow vehicle. Run the extension cord from it to the trailer shore power cord.

Note the 45 minutes won't put many AH back in even doing 50-80s.
Say you have a 60 amp charger and you are down 100AH /50%. 45 minutes will get you 45AH (minus a few for heat) so you are now at 145AH and you used 100 the first day, so by next day you are down another 100 to 45AH remaining.

Conserving to 50AH a day means you are down to 150/ 75% and where Bulk ends so your 60 amps will taper from the start doing the 75-90 so it will take longer. ( You don't do past 90 on generator on low amps and waste a lot of gen fuel for little return.) So you only are back to 180AH- restored 30AH of that 50. Next day you are down another 50 to 130AH and so on.

You could splurge the first day to get down to 50% and then do 50-90s. but in any case you will be running the gen for a couple hours a day or even longer depending, so you will need lots of propane or gasoline for it. Doesn't help if they are LFP--an AH is an AH no matter where it came from.

Having an EV for a TV you can plug into is very interesting--IMO that is the way to go if available. Nobody cares about efficiency while camping. You just want to get to tomorrow without freezing in the dark.

BFL13 wrote:

pianotuna wrote:
BFL13,

Given that SiO2 can do 4C continuously, and can be taken to 0% state of charge, why would you suggest that it takes 2 SiO2 to equal 1 LiFePo4?

Didn't mean to say that, if I did. You can use the one LFP or SiO2 with its own inverter to run the MW etc, and use the existing FLA bank for the rest.

100AH is just not enough of any kind of battery bank for a weekend off-grid in the winter. If you don't have the FLA bank you need two LFPs (no mixing--second must also be LFP) or two SiO2s ( might get away with mixing types with them, but not for me thanks) to run it all.

Two FLAs can't run the MW like one of those others can with its high discharge rating, and you still need lots of AH for normal furnace running etc, so that means two of the expensive ones to get just 200AH.

Weight is an issue for these guys with small RVs or they could just have four 6s. That means LFP for the single MW one.

Yep. Weight is definitely an issue for us. But for two reasons. The batteries are located under the bed and slightly behind the axle. The hitch actually gets lighter as you add batteries. Not on a one to one ratio, but it does get lighter. I like to keep the trailer hitch weight at around 10 percent or more on any trailer I’m towing. Nice thing about little trailers is you can literally use a “large person” bathroom scale to accurately measure it. :). Anyway. Adding another set of 6 volt AGM’s wouldn’t be an option for us. If we need more capacity it’s either

1. More solar (but we like to park in the shade so......)
2. A small propane generator to charge the 6 volts once per day for 45 minutes (prefer not doing this but maybe).
3. Switching to a set of LFP 100’s Pricey but doable and the cabinet is ready for them.

Once we start camping in the spring we’ll figure it out. Can’t wait.

BFL13,

Thanks.

pianotuna wrote:
BFL13,

Given that SiO2 can do 4C continuously, and can be taken to 0% state of charge, why would you suggest that it takes 2 SiO2 to equal 1 LiFePo4?

Didn't mean to say that, if I did. You can use the one LFP or SiO2 with its own inverter to run the MW etc, and use the existing FLA bank for the rest.

100AH is just not enough of any kind of battery bank for a weekend off-grid in the winter. If you don't have the FLA bank you need two LFPs (no mixing--second must also be LFP) or two SiO2s ( might get away with mixing types with them, but not for me thanks) to run it all.

Two FLAs can't run the MW like one of those others can with its high discharge rating, and you still need lots of AH for normal furnace running etc, so that means two of the expensive ones to get just 200AH.

Weight is an issue for these guys with small RVs or they could just have four 6s. That means LFP for the single MW one.

BFL13,

Given that SiO2 can do 4C continuously, and can be taken to 0% state of charge, why would you suggest that it takes 2 SiO2 to equal 1 LiFePo4?

You can keep your FLA bank for normal RV work (furnace etc) and also get an LFP for the microwave, kettle, toaster, and TV work.

That way you don't need two LFPs to get enough AH for furnace plus MW, etc. The one LFP can run the MW etc, leaving enough AH on the existing FLA bank for furnace etc.

No wiring changes or converter changes.

The LFP goes anywhere you can stash it inside where it is warm along with its own inverter (needs some air for location) On arrival camping, run an extension cord from the LFP's inverter to outside where you can plug in the shore power cord to the extension cord.

You recharge the FLA bank same as now. You need a portable charger to top up the LFP as required. Or use your converter with jumper cables over to the LFP. put them away after.

I have this sort of set up in the MH for the winter camping off grid. The existing MH set- up is the same as in the Profile, but have moved the two SiO2s (you would use one LFP) from the TC to inside the MH (on the floor behind a chair) with its own inverter connected to that bank.

I run the TV/DVD off that bank to keep those AH off the 6s, which gives them more furnace time. The MW etc can be run off the inverter on the 6s as usual, but I could plug all that into the other inverter.

In your cases, you would do it with the MW's inverter on the LFP and camp as usual off the FLAs for the other loads.

Big lesson I learned with the TC and one 100AH SiO2 (would be the same with one 100AH LFP) is it can run the MW just fine with the high amps, but you still need AH for furnace etc. which means you need 200AH.

The idea here is to save money by keeping your existing FLA bank to do the furnace etc, and now you can do the MW etc with just one LFP. You don't run the big stuff very long, so you don't need a ton of AH--just the high amp discharge the LFP can provide.

Note in this scenario the converter is not on the same bank as the inverter so no loop issues plugging into the shore power cable.

Ivylog wrote:
Why would you replace 2 new AGM batteries (good for 5+ years) with overpriced Lithiums…in 5 years the prices will be even lower. Assuming the cells I bought finally arrive, building a LifePo4 battery for $1/AH makes them price comparative with AGMs but 3X the cycles.

Yep. And that’s why We are going to live with the 6 volt AGM’s for awhile and see how it goes. I will jump through a few hoops to make it work if I can, but camping under trees kinda takes the solar solution off the table. We usually move every few days but we don’t go usually very far before we are in our next camping and hiking spot so on the road charging may not be very effective. So if it doesn’t work with the 2 X 6 volt AGM’s it’s either a little portable propane inverter generator or upgrade to a couple of 31 LFP’s. The trailer (and SUV) don’t arrive until early 2022 so until then it’s kinda watch and learn what others are doing.

Cheers.