Somewhat wacko battery/solar question

[EnzoColorado]

I have two 100 Ah Renogy AGM batteries in my TT, connected to two Renogy 100 watts solar panels on the roof via a Renogy 30A PWM controller.

I want to install an inverter so I can use coffee maker and microwave. Quick napkin calculation showed I don't have enough power in the batteries to run the coffee maker and microwave in the morning before the sun had a chance to charge the batteries.

I want to install another battery but this time a 200Ah LiFe battery. Can the Renogy 30A PWM charger charge both the AGM batteries and LiFe battery at the same time? Multiple reason for the LiFe batteries: more useable capacity than AGM, longer life cycles. The AGM batteries are 4 years old and I think when I need to replace them, it'll be LiFe batteries.

I don't think I need add more solar panels since the two AGM batteries usually gets topped off by 10 AM. We have good amount of sunlight here in Colorado.

My best guess is I can not mix AGM and LiFe batteries in the same circuit to be charged by the controller. But I hope I'm wrong.

[valhalla360]

EnzoColorado wrote:

valhalla360 wrote:
How low are the existing batteries come morning?

A 600w coffee maker should pull around 50amps for maybe 10min for a total consumption of around 8.5amp-hr. That seems quite reasonable off a 200amp-hr battery bank unless they are borderline covering the overnight consumption.

As previously mentioned, mixing different battery types (doubly so with different ages) is not recommended.

Usually low to mid 60% in the morning before the panels start to receive lights. I'm told that AGM batteries shouldn't be discharged more than 50% so I'm using 100amp-hr useable capacity in my back of napkin calculation.

With At 60%, that's 120amp-hr left in the batteries come morning. You have another 20amp-hr remaining before you hit 50%, so pulling 8-9amp-hr to run the coffee maker shouldn't be a big problem.

When those lead-acid batteries die, uping the usable amp-hr a bit might be nice but sure looks like it's doable with the current setup.

[Grit_dog]

Get a French press. Not so wacky. $20 solution to needing electric coffee pot and better tasting coffee.
It’s a bit of a project but not horribly expensive to “split” the systems. Another Li compatible charge controller and the right Perko switch is pretty cheap. Then you could use separate DC sources with the turn of a knob.
Maybe good stop gap for a couple years.
Question though, why not just try it now and see if it works?

[pianotuna]

Leave the system alone until the agm batteries need replacement.

Why? Technological change. Prices are continuing to drop on Li batteries, too.

Replace with Li when the times come so long as there is no cold camping.

[Lwiddis]

There’s no “magic” in not exceeding a 50% depth of discharge. The number of cycles does not radically decline at 60% vs. 50%. See https://www.trojanbattery.com/pdf/AGM_Trojan_ProductLineSheet.pdf

[CA_Traveler]

EnzoColorado wrote:
Sounds like I should just get an pure sine wave 2K inverter and give my current batteries a try before getting fancy with adding lithium batteries. If this works, then in a few years when I replace the AGM with lithium, I'll simply have even more power to spare.

Good plan and you can discharge to 20% SOC. But you have to replace those AHs which might be problem on overcast days... Maybe more panels.

And all chargers should be Li compatible.

[EnzoColorado]

3 tons wrote:
Well, lets assume your two batteries total about 200a/hrs, with a lower available limit of say a 50% depth of discharge…And since with 200w of solar, your batteries are typically topped off by 10:00am, let’s then assume that at about 75’ish % average PV efficiency you recovered maybe 15a/hrs from sunrise to 1000, which would hypothetically suggest a morning awakening SOC low of about 85% - If my guess is close (??) I’d call that fairly high!!

FWIW, with my former two Golf Cart 6v, I had no problem running a 1300+w Keurig coffee maker repeatedly (typically about a 2 min brew per cup), using a 1800w inverter, but not so with a 1500w microwave, because microwave’s are heavily ‘reactive’ loads (coffee makers are resistive)…So, I swapped out the power sucking 1500w Microwave for a far more ‘RV practical 850w Panasonic model’ which actually works out just perfectly!

Eventually I switched to a *better 2k watt pure-sine pass-thru (shore power) inverter-charger and using the same GC batteries could even run the 11kbtu Coleman air conditioner for short periods (compressor cycling, concurrent with solar), so with a coffee maker you should have no problemo!

To prevent nagging battery-to-inverter voltage sags (and inverter alarms - ugg…) its best to use robust sized battery cables - mine are heavy 0004 ought… Also, beyond the all the marketing hype behind inverter ‘advertised watt ratings’ you’ll also want to know the inverter’s surge rating and the duration of surge condition…Know that not all inverter’s of the same wattage rating will handle a reactive load in quite the same way - Models that don’t spec these additional two stats should not be considered - JMHO…

*4500w surge or 5 sec

FWIW, I’ve since ditched the GC batteries in favor of Lithium, which offer very little voltage sag along with a uber deep depth of discharge (DOD)…

Hope this Helps 🙂

3 tons

This is really good info.

Sounds like I should just get an pure sine wave 2K inverter and give my current batteries a try before getting fancy with adding lithium batteries. If this works, then in a few years when I replace the AGM with lithium, I'll simply have even more power to spare.

Thank you for all the replies!

[3_tons]

Well, lets assume your two batteries total about 200a/hrs, with a lower available limit of say a 50% depth of discharge…And since with 200w of solar, your batteries are typically topped off by 10:00am, let’s then assume that at about 75’ish % average PV efficiency you recovered maybe 15a/hrs from sunrise to 1000, which would hypothetically suggest a morning awakening SOC low of about 85% - If my guess is close (??) I’d call that fairly high!!

FWIW, with my former two Golf Cart 6v, I had no problem running a 1300+w Keurig coffee maker repeatedly (typically about a 2 min brew per cup), using a 1800w inverter, but not so with a 1500w microwave, because microwave’s are heavily ‘reactive’ loads (coffee makers are resistive)…So, I swapped out the power sucking 1500w Microwave for a far more ‘RV practical 850w Panasonic model’ which actually works out just perfectly!

Eventually I switched to a *better 2k watt pure-sine pass-thru (shore power) inverter-charger and using the same GC batteries could even run the 11kbtu Coleman air conditioner for short periods (compressor cycling, concurrent with solar), so with a coffee maker you should have no problemo!

To prevent nagging battery-to-inverter voltage sags (and inverter alarms - ugg…) its best to use robust sized battery cables - mine are heavy 0004 ought… Also, beyond the all the marketing hype behind inverter ‘advertised watt ratings’ you’ll also want to know the inverter’s surge rating and the duration of surge condition…Know that not all inverter’s of the same wattage rating will handle a reactive load in quite the same way - Models that don’t spec these additional two stats should not be considered - JMHO…

*4500w surge or 5 sec

FWIW, I’ve since ditched the GC batteries in favor of Lithium, which offer very little voltage sag along with a uber deep depth of discharge (DOD)…

Hope this Helps 🙂

3 tons

[EnzoColorado]

valhalla360 wrote:
How low are the existing batteries come morning?

A 600w coffee maker should pull around 50amps for maybe 10min for a total consumption of around 8.5amp-hr. That seems quite reasonable off a 200amp-hr battery bank unless they are borderline covering the overnight consumption.

As previously mentioned, mixing different battery types (doubly so with different ages) is not recommended.

Usually low to mid 60% in the morning before the panels start to receive lights. I'm told that AGM batteries shouldn't be discharged more than 50% so I'm using 100amp-hr useable capacity in my back of napkin calculation.

[EnzoColorado]

campinghut wrote:
What is draining your batteries during the night. 200AH even 100AH should be enough for the coffee maker (one pot) for sure and the microwave will depend on the length of time. Maybe I am out to lunch on the amount of power needed

We have a fridge that uses propane but the circuit uses the battery all night. In the evening, we have lights (all LED's), water pump and water heater that uses battery. Usually by the early morning before sunrise, the controller indicates 62 to 65% with voltage around 12.4. But the camper's own battery indicator usually shows 3 to 4 lights out of 4 lights.

I'm under the impression that AGM batteries shouldn't be discharged more than 50%. Hence the hesitation about using them in the morning for coffee maker or microwave.

[SJ-Chris]

Since your title has the word "wacko" in it, I let my brain wander for an unusual solution for you...lol

Even though I've never heard of anyone doing this with their solar setup, it seems like it would be possible for you to run the lines from your solar panels into TWO solar charge controllers... One for the AGM batteries (the one you already have) and another new solar charge controller that would only go to your new lithium battery. Each solar charge controller would handle their job appropriately. The same solar panels could charge both of your independent, different type/age "battery banks". You wouldn't want to physically connect these two battery banks as they are different types. But you could hook up a different inverter to your lithium battery to use it's power for 120v items. Side note: I'm not that familiar with lithium batteries so I don't know if just one is enough to power a microwave and handle the heavy amp pull.

Just an idea....

-Chris

[time2roll]

No don't mix those batteries. I would give it a go as is. Napkin calculation could be off a bit.
Go ahead and run hard on those AGM. Then switch to LFP when they are shot.

[Lwiddis]

You are currently on the edge of adequate solar watts to battery amp hours. One to one is the minimum. I agree with campnghut, something in your system isn’t right.

[jaycocreek]

Can the Renogy 30A PWM charger charge both the AGM batteries and LiFe battery at the same time?

I have a Renogy 30A PWM connected to a single 100AH LFP with aligator clips so I can charge whatever battery or bank I want..I use this particular battery for coffee maker/microwave and hot plate and kept close to fully charged,it does the job..If I need more charging of something else.I just use the aligator clips on that battery bank...Weird maybe to some,but it works for me..

So,yes you can use that controller on two different battery banks independently, but not at the same time with alligator clips or by just changing which batteries are connected to the Renogy.

Good luck..

[valhalla360]

How low are the existing batteries come morning?

A 600w coffee maker should pull around 50amps for maybe 10min for a total consumption of around 8.5amp-hr. That seems quite reasonable off a 200amp-hr battery bank unless they are borderline covering the overnight consumption.

As previously mentioned, mixing different battery types (doubly so with different ages) is not recommended.