emergency power setup if grid goes down

[stormtracker78]

hi i was thinking about getting one of the renogy 400 watt kits or hqst with a bougerv 40 amp mppt with fuses etc and having it set ready for any longterm powwer outtage or hurricanes hooked to 2 agm 100 amp batteries when i need to hook it up.Here is my question i just wanted to use the agm batteries during the day when there being charged to power a 35 amp lithium battery charger for seval 100 amp lifepoe4 batteries .from what i researched it should only take a hour and a half to charge them.is this a good idea for a short to medium power outage term?i dont know how many watts the battery chargers pull.i have a bestek 500 watt pure sinewave inverter i was going to use to power the charger.thereby rotating my lithium batteries when they need charged .i was going to have one for my bougerv fridge and the other for my sw radioes and another for charging batteries aa running a fan at night etc

 

[Brucey]

Can you connect the solar controller to the LFP batteries directly, instead of wasting energy with a dc->ac-dc conversion?

 

[45North]

I'm not too clear on what you're planning to do.
Lithium batteries have very low "self discharge" so you can go for months between charges if you're not using them. So you'll only need to charge them if you use them.

 

[Decto]

On a long, bright sunny day, a 400W panel may provide enough to recover the SLA batteries from recharging 1 x LiFePO4 100AH
In heavy cloud it could take several days, if not the best part of a week to charge 1 battery.

Agree with above, better to have extra Lithium and just swap when charged rather than have all the conversion losses.

 

[stormtracker78]

Basically I'm just trying to have a recharge station for my lithium batteries if say a hurricane hits us and we're without power for several months or the grid goes down and yes lithium has low self discharge which I love but eventually they're going to have to be charged in a scenario like that oh and yes obviously I can hook the mppt directly to the lithium batteries that's what they're made for but outside of a victron which I can't afford everywhere I research especially with renogy and other mppts hqst etc they are not really made for Life poe batteries the only way to do it is a custom setup and thew respective Bluetooth I did research bougerv they seem to have a good report with lithium I hear renogy with the bt1 is the worst same for hqst and I was just curious if it's just easier to set up a charging station like that because all of those mppts do work well with agms to use the AGM as my power source for recharging my lithium so when one gets to the point it needs charge I charged it up and then I put it to use they're by cycling them so I'm not without power for the fridge and other essentials it's just I don't know how much watts these 35 amp lithium battery chargers use but I think it would be a good idea because I can use the AGM batteries which are being charged to charge up my lithium and then when I don't need them the agms will maintain their charge through the mppt until the power comes back on (hopefully we were without power for 2 months two cities over from hurricane dolly couple years back and that was just barely a category 2) of course I could use a lithium to do the same thing but the problem is I don't want to have to set up a custom profile in any of the mppts and I hear so many mixed reports when it comes to lithium mppt outside of the victron which I hear is excellent

 

[Bud Martin]

hi i was thinking about getting one of the renogy 400 watt kits or hqst with a bougerv 40 amp mppt with fuses etc and having it set ready for any longterm powwer outtage or hurricanes hooked to 2 agm 100 amp batteries when i need to hook it up.Here is my question i just wanted to use the agm batteries during the day when there being charged to power a 35 amp lithium battery charger for seval 100 amp lifepoe4 batteries .from what i researched it should only take a hour and a half to charge them.is this a good idea for a short to medium power outage term?i dont know how many watts the battery chargers pull.i have a bestek 500 watt pure sinewave inverter i was going to use to power the charger.thereby rotating my lithium batteries when they need charged .i was going to have one for my bougerv fridge and the other for my sw radioes and another for charging batteries aa running a fan at night etc

35A charger lets say at 13V = 455W and if you take in the charger efficiency, lest say 90% then it will be 505W.
you have 100Ah LiFePO4, so to charge from empty to full with 35A charger it will be about 100Ah/35A = 2.6 hours.
Your 400W system will more likely to put out about 80%, you are not going to get 400W.
So why do you use your Solar charge controller to charge the LiFePO4 directly?
BTW, two 100Ah AGM batteries have about 100Ah of usable capacity.

 

[stormtracker78]

Awesome bud ty! I needed that math on the watts I can hook the solar directly to the lithium battery threw the mppt normal just click lithium setting but I don't want to risk it because I hear so many bad reports on these mppts that they don't shut off and they do the float charges wrong and a whole bunch of stuff so I was like I'll just use one or two cheap agms invest in couple lithium and then just charge them with the AGM p even with the loss is in such where I live it's almost constant Sun so I can just do pass-through charging to the agms to the inverter to the lithium charger to my batteries because this is only a setup for a hurricane or if the grid shuts down but if anyone knows a good solid mppt that is not victron and is economical let me know that works well with lithium

 

[12VoltInstalls]

35A charger lets say at 13V = 455W and if you take in the charger efficiency, lest say 90% then it will be 505W.

You are smarter than me I think but I believe you will find most chargers closer to 50% efficiency. Or maybe I just buy chargers that are too low priced?

I wouldn’t count on 505W

Unless my lack of knowledge on DC2DC chargers comes into play. Maybe they have less losses due to no rectifying?

One of my 120VAC input chargers set at 8A 14V output I would and did guess at ~1.xA 120V but by accident when top charging two 140Ah lithiums I discovered it was 2.3A on my Klein clamp meter.
It made sense after I thought about rectifying to DC.

 

[stormtracker78]

Yea Amazon's got a hole section devoted to reneogys 40 amp mppt how terrible it is with lithium and the Bluetooth module and also a lot of the popular others that's why I'm thinking about just a simple way to keep the agms charged and only use them when I need them and since I'm only going to be 1 to 2 hours charging per day I have the rest of the day to keep them maintained shouldn't deplete them that much anyway because my panels will be at full occupancy whatever percentage there is I live in South Texas we get 6 Plus hours of Sun very few clouds and I don't have to worry about low temp for the lithium so basically it's just a way to keep those lithiums charged when they start running low again this is only for emergency purposes a set up for maybe say four months at the most but it's self-generating in case it goes longer and again I can use a lithium battery instead of the Agms to charge the others but I've got to make sure I've got a good mppt that won't fry those batteries because it's doing the AGM settings over the lithium and I hate custom setting because every lithium battery I believe has mostly the same settings with minor variations so the custom settings have to be accurate if I had the money I'd get a victron and I can always add more solar panels if I need to once I get my original setup setup I just need to make sure the mppt can handle it most 40 amps can do 500 watts anyway and then there's the option of doing it in series The main thing was I needed to know about how many watts do those lithium battery chargers run at 35 amps that's the main numerical component on however I set up my system because as we all know a 100 amp hour AGM actually is only 50 not going below 500 watts hence the two agms if the lithium charger was around 4 or 500 watts per hour to charge

 

[12VoltInstalls]

hate custom setting because every lithium battery I believe has mostly the same settings with minor variations so the custom settings have to be accurate

There’s only three or basic settings for lithium with ‘custom’ as opposed to manufacturer presets.
Lithium only needs initial charge voltage, disable equalize or set it to 1minute at bulk settings, and set float to 13.8, and a high voltage disconnect ~14,7V

Nothing to be afraid of. The manufacturer presets are basically those above or a variation on agm settings. It just happens to be a menu option instead of a manual entry parameter

 

[stormtracker78]

Ty 12voltinstalls so then I guess your saying the custom settings on the renogy and hqst and other of the more economical mppts are not that hard to configure on custom therefore just use a lithium batteriy to charge the others instead of two Agms which would be more practical in the long run due to the dod but also the fast recharge time it would have from my solar panels to recharge itself after recharging the rotating lithium batteries compared to AGM recharge times it would be nice if I could have just a single battery Bank with everything hooked up to it but I have to have a dedicated battery for the fridge dedicated battery for my radios IE my icom and alincos and a dedicated battery for a recharging the double A's etc this is my radio setup I created did all the wiring by myself with the rig runners etc

 

[12VoltInstalls]

guess your saying the custom settings on the renogy and hqst and other of the more economical mppts are not that hard to configure on custom therefore just use a lithium batteriy to charge the others instead of two Agms

Basically, yes.
However - I would probably be disinclined to buy renergy or hqst in that price range.

I like the Epever product a lot but until or unless I figure out a resolution to Epever occasionally, randomly deciding not to maintain charging for the rest of a day once full charge has been achieved I recommend them with a caveat.
In the renorgy price range there’s Epever. A bit below that pricewise is Ampinvt. Super-cheap is PowrMR.

In my mind lately I’ve been leaning heavily towards Victron, or going cheap with powrMR. If I’d already got the Epever to not have dropouts anymore I’d be quite happy with Epever

 

[stormtracker78]

Basically, yes.
However - I would probably be disinclined to buy renergy or hqst in that price range.

I like the Epever product a lot but until or unless I figure out a resolution to Epever occasionally, randomly deciding not to maintain charging for the rest of a day once full charge has been achieved I recommend them with a caveat.
In the renorgy price range there’s Epever. A bit below that pricewise is Ampinvt. Super-cheap is PowrMR.

In my mind lately I’ve been leaning heavily towards Victron, or going cheap with powrMR. If I’d already got the Epever to not have dropouts anymore I’d be quite happy with Epever

Thank you but as you can see this is the whole reason I want to just do AGM any one of the mppt's renogy hqst etc epevers all of those are great with agms no problems so that's why I'm seriously considering just doing an AGM battery bank and charging my lithiums off of that it would really be nice if they could make an mppt economical for lithium batteries I really hear that bougerv is pretty good

 

[12VoltInstalls]

any one of the mppt's renogy hqst etc epevers all of those are great with agms no problems

Not true.

I’ve had to face the Epever issue on lead acid as well. It’s a bug. Not a lithium problem because other SCCs do not have any issues merely changing wires over. That’s why caveat on Epever

renorgy and hgst is just spec-box commodity private labels. Buy from someplace else that cares about branding and marketplace longevity imho
hqst panels are fine. That same panel is sold with a number of ‘brands’

Ampinvt and powrMR on the bottom shelf reportedly do not get confused with floating fully charged batteries according to my exhaustive reading and looking at a few dozen youTubish vids

Victron is a no brainer other than the coffers being maintained at a vacuum

 

[stormtracker78]

Ty yeah Amazon's got a good deal for 4-hqsts and I have a renogy panel already the old 100-d the panels are not a problem they're actually pretty good for the price it's just finding a well-rounded Mppt that doesn't break the bank lol