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Solar help
Snik is here and trying to figure out what she needs.

She has an Engle fridge that is about two foot by 16”. She wants to keep it plugged in of course.

She wants to recharge her phone and IPad once a day.

She has an induction cooktop that is 1700 watts but she only turns to about 200-400 watts. She will use that for about ten minutes a day.

She has a little battery charger for double A batteries and she recharged about once a week or so.

That’s about it.

She has a Ford Transit Connect minivan

How much solar and how much battery please.
What model is her Engle?

How do you know if your induction stovetop is at 200w? I have a 1500w inverter and my induction popped fuses.
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as much as she can get on the vehicle
[-] The following 2 users say Thank You to justjim for this post:
  • Cammalu (10-07-2019), heron (10-07-2019)
The battery I would choose, depends on how much solar can be stuffed on the roof, and whether the alternator is going to contribute to charging, and perhaps contribute to powering induction cooker. Will she be plugging into the grid to recharge the battery occasionally, and if so, how occasionally?

Its basically impossible to have too much solar, but far too easy to have too little. Too much usually means a happy long lived battery and a non chalance about electrical usage, not enough means constant stress about maximizing exposure to sun and minimizing electrical usage.

The engle on a 75 degree day( inside the van) will use about 1Ah each hour, hopefully and likely less. If it is asked to do its job in a 95 degree locked up closed up van, double that figure. 105f double that again.

I don't know how much a charging Ipad consumes, for how long. 2.1 amps@5v (10.2 watts) for 1 hour? 2 hours, 3? no idea. Is it going to be fully dead when asjed to be charged, some fraction of that, any idea of that fraction.

Same for the cell phone, i know mine maxes out at about 5 watts, but I know some others can take 10 or 15 watts.

The battery is going to have to maintain enough voltage to power the induction cooker for the time required, through the inverter.

Lets use 400 watts as the load and battery maintaining 11.5v, in a morning situation when the battery is discharged as low as it generally goes. That is a 34.8 amp load, but we need to add 15% for inverter inefficiency, and perhaps 20% would be more realistic, so another 7 amps.

So 42 amps to induction cook through inverter at 400 watts. That is a considerable load. The starter motor is about 180 amps, for 2 or 3 seconds and a relatively large 12.8v healthy battery struggles to maintain 12v+ during engine cranking.

A single battery is not going to be all that happy to supply the induction cooker at less than full charge, especially not at lower states of charge. and not after many days of cycling and not reaching true full charge.

A tppl AGM battery like Northstar or Odyssey has very high CCA figures due to very low resistance. these are great batteries for powering high loads, but they are not good 'solar only' batteries. When deeply discharged they need high amp recharging, regularly, from a low state of charge, to give good service. Odyssey says no less than 40 amps for their 100Ah group 31 battery when deeply discharged.

If one wants just one single battery to reliably power the induction cooker, then the TPPL AGM$$ are the best lead acid battery choice, but you cant just feed them whatever charging current is available from solar, and expect them to maintain that performance. More solar is obviously better but 40 amps is not going to fit on a transit van roof and its not like the instant the sun rises the panels full output is available.

Now if one is going to be able to plug in every 7 to 10 days or so, and gets a 40+ amp charger/converter and applies that charger at a low state of charge and holds it until the battery is full, they can keep the TPPl AGM fairly happy.

Batteries plus sells relabelled Northstar batteries as X2 power. They are not cheap. I've gotten tremendous service from my Northstar group 27, but I can and do feed it the high amp recharge regularly.

If one cannot feed their battery properly, they just replace it more often and likely at an inconvenient time. If they treat it very poorly they then get to deal with trying to get the store to warranty it.

So John, how much solar can she fit on the roof?

a Lifepo4 battery is very good at maintaining voltages at lower states of charge but they are a whole different animal that i have no experience with, and would not recommend a newb to set up, or have set up, unless they got loads of money and find a legitimate pro to set it up properly, not cut corners, and be able to instruct the owner on the proper use and care of the system.
[-] The following 3 users say Thank You to sternwake for this post:
  • rvpopeye (10-07-2019), Gapper2 (10-07-2019), Snikwahjm (10-07-2019)
The cook top would be the issue. The fridge did work fine off 200 solar and one marine battery. John says I could get 400 watts solar on my roof.

The fridge runs fine off the car battery when I am moving, I would assume there might be some way to charge a battery when the vehicle is moving.

How come induction cook tops are sold as being energy efficient?
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They are energy efficient in that the electricity they consume is used more efficiently, ie., 90+%? efficient rather than the 80%? efficient regular use. This doesn't mean they use a LOT less power than other comparable devices. These are meant for household use where you are trying to keep the energy bill down. Hopefully someone can explain it better.

I use propane for cooking. It is a LOT more efficient (cheaper) than electricity. Anything you can make work off native 12V or use propane for is better. I have a small inverter and don't remember the last time I used it. Any heavy electrical hitters (microwave/convection oven/coffee pot), I use the generator.

My electronics charge from 12V. The USB chargers are 12V and the computer/TV are upconverted from 12V to 19V. Use car chargers for anything you can.

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If you leave out the induction cooktop, I feel certain she can get by with 200 watts of portable panels, 300 if flat and roof mounted.

Induction cooktops are fine at home...or IF you have PLENTY of solar power, but in a small vehicle with limited solar, it will not work well.

She should buy a small propane or butane stove and not try to heat or cook with solar powered electricity (PV).

A 100 ah lithium OR 200 ah of lead acid will be plenty, and carry her thru a few days of cloudy/rainy weather.

She will need to camp in sunshine from then on, camping in the shade of big trees will not work well UNLESS she can carry 200 watts of solar panels out into the sun.
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[-] The following 1 user says Thank You to tx2sturgis for this post:
  • frater secessus (10-08-2019)
Something to keep in mind, (I didn't know until recently) If you have 400w solar, do not get batteries with more than 400AH.

Not that I have to be concerned in my current state.
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DC Compressor Fridge consumption is not a huge draw. Mine is about 32 watts running with a 55 watt surge for a half second when it first fires up and pretty much never runs more than 20 minutes per hour. Your Engel will be similar.

Induction cooktops are more efficient than regular heating coils, but heating anything using electricity, uses a lot of electricity. There is no way around that, and batteries simply cannot store very much.

Charging of batteries while driving is of course possible and should be utilized. However one is at the mercy of their vehicle's voltage regulator as to how effective the charging while driving is  The VR was not programmed to recharge an additional depleted battery, it was designed to keep a lightly depleted starting battery from overcharging, and as such it charges much slower than what the  battery owner  and depleted house battery itself would like.

All vehicles will vary widely as to how much electrical pressure (voltage) they allow, and for how long.  2/3rds more amperage will flow into a battery with 14.7v at battery terminals than will at 13.7v, but many vehicles will allow 14's only briefly then drop to mid 13's. A battery being held at ~14.7v is as fast as it can safely be recharged, 13.7v is a fraction of that and an unhealthy battery will never reach full charge at 13.7v, not even if held at that voltage for weeks.

The battery accepts as much amperage  as it wants, at the voltage reaching the battery terminals, upto the limits of the charging source.

Some more modern vehicles might intentionally allow the starting battery to remain only ~80% charged.  They do this to try and boost the MPG's slightly, at the expense of battery life.  It's Asinine really, but tiny percentages in fleet fuel economy means millions more in profit, for them, and everything this day and age is about maximum profit, Honor be damned.

If you can get 400 watts on the roof, do so, and get about 200 AH of AGM battery.  A PD 9245 or PD9260 or PD9270 converter would be great for the AGMS when you can plug into the grid. A 40 amp Renogy dc to dc charger/isolator will at least maintain 14.4 ish volts  while driving, whenever the house battery is not full or close to it.


These DC to DC chargers will both isolate house battery from starter battery, and take whatever vehicle voltage is allowed and step it up or down, though stepping it down will likely be a rare occurrence..  Renogy has new products in 20 and 40 amp flavors for doing this for significantly les$ than other products meant to do the same thing.
I've no experience with them, their efficacy or reliability.

The TPPL AGMS (Northstar/Odyssey) are second only to Lifepo4 in voltage retention under high loads such as an induction hot plate.  They will stand a much better chance of keeping the low voltage alarm on the inverter from screaming at you, and then shutting off before your food is cooked.  I would say get two group 24 or group 27 or group 31 batteries in parallel, with fat copper parallelling them and fat copper to the inverter.  Other premium AGM like Lifeline do not have the super high CCA figures, but they do want as high a charging current as possible at all times, like TPPL agms.  Lesser $$ AGMs do not have the same ability to hold high voltage under high loads as TPPL, but are better than most flooded marine or deep cycle batteries in this regard.

Beware than AGM is the new 'magic' battery, according to automotive forums and autoparts stores.  AGMS marketed to this crowd will have more attractive prices than any TPPL or Lifeline or even other AGMS marketed towards deep cycling, like Vmaxtanks on Amazon.  Yet these parts stores AGMS are primarly cost cut AGMS intended for starting duty only, even if their sticker says clearly 'deep cycle"  beware of marketing lies and deceptions, always.
  Do not expect the voltage retention or ability to accept huge charge currents and ultimately the same cycle life as a higher $$ AGM that is treated right. If the battery is not treated right then by all means go cheap as no lead battery is immune to improper recharging, or being regularly over discharged.

On another rv forum a guy has a large bank of minimum $$ Chinese AGMS, some 450AH worth, and now at 75% charged or less their voltage crashes  and his inverter shuts down entirley when he runs his toaster or microwave or Kettle.  These batteries are still fine for lesser loads and deep cycling, but are now inadequate for powering the higher loads when discharged below 75%, and this guy can and does recharge as well as possible with proper told devices and interest in doing so.  

Some people like a lot of battery capacity, then have way too little charging source for those batteries when they are well depleted
. I like minimal battery capacity and more charging capacity, but  here one enters the  specific intended use philosophical debate a billion variables, and  opinion, and I'll exit stage left.

Regardless AGMS that were discharged to the 50% range regularly need at least a 2 watts of solar to 1Ah of battery capacity in a good sunny environment in the hotter 6 months of the year, and preferably 3:1 ratio, and up north in the colder 6 months likely need well more than that, depending on the availability of other charging sources

Fear of propane will be expensive.
(10-07-2019, 11:57 AM)sternwake Wrote:
Regardless AGMS that were discharged to the 50% range regularly need at least a 2 watts of solar to 1Ah of battery capacity in a good sunny environment in the hotter 6 months of the year, and preferably 3:1 ratio, and up north in the colder 6 months likely need well more than that, depending on the availability of other charging sources

Fear of propane will be expensive.

Then AH:w I'm about perfect ... that's good to know. I still have about 50 more Watts than AH.
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