Portable LiFePO4 and Solar beginner help

[Jman]

Hello all, I need some help for charging Lithium off solar.
I'm Looking to build a small portable camping setup using two Fusion Lifep04 100ah batteries that each has its own built in bms. Keeping them separate & charging one at a time using one or at times two 250watt panels in parallel.
The specs of battery say min charge current is 10amp, std 30, & max 70.

So is there a problem with not getting much sunlight? If I had a single 250watt panel that can deliver up to 12amps max per hour. But it's not going to always get that much. In fact most times there are clouds. And the angle of sunrays are not straight on.

So does this mean to properly charge the battery I would need to be constantly over 10amps charge current?

That 10amp miniumum sounds like a threshold on/off in the circuit & that the battery will only charge in full sunlight.

Another problem is finding a small PWM lithium regulator? I read that the regulator might not work well with the batteries bms, not sure what that really means.

Can someone suggest some cost effective waterproof PWM or MPPT Lithium regulators.

Finally given that lithium likes to stay at around 50-60%SoC & that there are appliances constantly drawing power like fridges, I thought two separate batteries in their own carry box with own regulator are better than one large battery, or else a single large battery will stay in a high SoC throughout a trip. So I would charge one fully then disconnect solar input right before running a slow drawing appliance, while the other battery is being charged up on it's own.
This along with lithium's fast charge time would seem to work well with my set & forget panel approach where panels are only going to get 2-3hrs of light a day max. Do you think this is a good strategy?

Please advise me, thanks

[Mike90250]

Welcome. and prepare for a lot of reading and learning.
Li batteries like to be STORED (long term) at 50%. In actual use, use them at 20% (low end) to 90% (high end) to get the most power of out them, and after a trip, store at 50%

I'll assume the voltage is 12V ? and the 250w panels are close to 30Vmp ? That means if you use a PWM Controller, you have reduces your panel to a 125W panel. But if you use MPPT controller, you retain the 250W capability, which you will need with short sun hours and poor exposure.


Finally, run both Li batteries in parallel with each other, so they share the Loads and charging. Much better than flattening one battery when you forgot to change it over to the full one.

Since you have chosen to depart from normal 12V lead acid tech, you now get to learn to program your controller, LVD and insure your gear all works together well. You have to read the specs, I have no idea what you bought and if it's compatible with each other.

[Sunking]

Can someone suggest some cost effective waterproof PWM or MPPT Lithium regulators.

You are SOL, none made. I guarantee you this is not going to work out for you. You do not even know what questions to ask. Don't worry we have Karrak to straighten you out and will tell you how to destroy your batteries.

FWIW all you need is a 14.4 volt source using a MPPT controller.

[Jman]

I'll assume the voltage is 12V ? and the 250w panels are close to 30Vmp ? That means if you use a PWM Controller, you have reduces your panel to a 125W panel. But if you use MPPT controller, you retain the 250W capability, which you will need with short sun hours and poor exposure.

Its nominal 12V & 21Vmp. Can you explain how the panel gets reduced to 125W?

[Sparkletron]

You don't need a waterproof controller; you need a waterproof box that you can put your batteries and controller in. Something with wheels and a collapsible handle will let you move it around the campsite with ease. Using an inverter? Put that in the box as well.

Google portable power box or solar generator. Lots of DIY examples.

[karrak]

Hello all, I need some help for charging Lithium off solar.
I'm Looking to build a small portable camping setup using two Fusion Lifep04 100ah batteries that each has its own built in bms. Keeping them separate & charging one at a time using one or at times two 250watt panels in parallel.
The specs of battery say min charge current is 10amp, std 30, & max 70.

So is there a problem with not getting much sunlight? If I had a single 250watt panel that can deliver up to 12amps max per hour. But it's not going to always get that much. In fact most times there are clouds. And the angle of sunrays are not straight on.

So does this mean to properly charge the battery I would need to be constantly over 10amps charge current?

That 10amp miniumum sounds like a threshold on/off in the circuit & that the battery will only charge in full sunlight.

The 10A minimum charge current doesn't sound right. There should be no minimum charge rate for the individual LFP cells in the battery and I can't see why the BMS would need a minimum charge current to work. Have you tried to charge the battery with a lower charge current or contacted the manufacture/supplier to see why there is this requirement?

Another problem is finding a small PWM lithium regulator? I read that the regulator might not work well with the batteries bms, not sure what that really means.

It is possible that the charge voltage being switched on and off by the PWM controller when it is regulating the voltage will upset the BMS in the battery. I would stick with an MPPT controller

Can someone suggest some cost effective waterproof PWM or MPPT Lithium regulators.

I think you will be battling to get a waterproof MPPT charge controller. You want to get a 20A controller where you can manually set the bulk/absorb and float voltages. The Epever charge controllers should work OK.

Finally given that lithium likes to stay at around 50-60%SoC & that there are appliances constantly drawing power like fridges, I thought two separate batteries in their own carry box with own regulator are better than one large battery, or else a single large battery will stay in a high SoC throughout a trip. So I would charge one fully then disconnect solar input right before running a slow drawing appliance, while the other battery is being charged up on it's own.
This along with lithium's fast charge time would seem to work well with my set & forget panel approach where panels are only going to get 2-3hrs of light a day max. Do you think this is a good strategy?

If the batteries are in use all the time with appliances like fridges connected to them there is no problem running the battery at nearly 100%SOC while the sun is shining. We have been doing this for nearly five years with no noticeable change in our LFP battery performance. When you get back from a trip I would discharge the batteries down to around 50%SOC and disconnect them from everything until you need them again. I would run both batteries in parallel, halving the charge and discharge currents by putting two batteries in parallel will increase their lifespan.

Are you in Australia by any off chance?

Simon

Off grid 24V system, 6x190W Solar Panels, 32x90ah Winston LiFeYPO4 batteries installed April 2013
BMS - Homemade Battery logger github.com/simat/BatteryMonitor/wiki
Latronics 4kW Inverter, homemade MPPT controller

[SunEagle]

Its nominal 12V & 21Vmp. Can you explain how the panel gets reduced to 125W?

Based on how a PWM works (amps in = amps out) you will lose a percentage of the panel wattage.

The panel wattage is calculated by multiplying the Vmp x Imp.

As an example a 250 watt panel probably has the Vmp ~ 24v and the Imp ~ 10.5amps (24 x 10.5 = 252w)

The PWM will only use that 10.5 amps for charging. If it is a 12volt battery then you will get 12v x 10.5a = 126 watts.

That is how a 250 watt panel can be turned into a 125 watt panel.

[Sunking]

Its nominal 12V & 21Vmp. Can you explain how the panel gets reduced to 125W?

Very simple.

PWM Output Current = Input Current.
Power = Voltage x Current.

Now take a look at your panel Imp (current @ max power). it should be roughly 12 amps right. Do the math 12 volts x 12 amps = What?

MPPT Output Current = Panel Wattage / Battery Voltage. 250 watts / 12 volts = What?

[Mike90250]

Its nominal 12V & 21Vmp. Can you explain how the panel gets reduced to 125W?

That's a very odd panel, to be that high wattage and low Vmp.

But, the way PWM controllers work, they simply connect the panel to the battery via a transistor and that turns your 21V panel into 14V. Panels are current sources. Working the math backwards, to get 250W @ 21V, the panel puts out 11.9A That's all the amps the panel can produce, so 11.9 x 14v at the battery gives you 166watts. not nice, nearly 100w wasted away.

MPPT controllers have a smart DC-DC converter circuit that keeps the panel properly loaded and produces 97% of the panel output to the battery, only a few % is lost as heat