Dehydrator math: Pineapples

For today’s issue of dehydrating math, I did not count the weight of the core, skin or green leafy top. At least where I live, pineapples are not sold by weight but rather priced per unit. I paid 4$ Canadian for this one.

pinapple fresh

Like before, I weighed the pineapple before and after dehydrating.

pineapple with water

I accidentally set the scale to pounds, but it’s easy enough to convert to grams, 787 of them.

The pineapple filled up my entire 4-tray dehydrator to 100% capacity exactly.

pineapple dehydrated no waterDried out, the pineapple is shockingly light – 123 grams, a tiny 15% of initial fruit weight. It would be even smaller, like 8% if we also counted the rind, core and leafy green hat.

component of pineapple

Even though I intentionally did not weigh the full pineapple, I am beginning to wish I had so this data would be even more useful. Next time I promise!


How long will my lead acid battery last before I have to charge it again?

Someone posted this question in the Vandwellers subreddit. Here was my answer with 2 very simple formulas.

lead acid deep cycle battery

If you multiply together your amps per hour and your volts in your battery, you can find how many watts per hour are inside your battery. Let’s use this battery as an example.

35 (amp hours of this battery, unit AH in the above link) x 12 (volts of this battery) gives you 420 watt hours (wH). 2 of those batteries like you have, will give you 840 watt hours.

    35 x 12 x 2 = 840 watt hours

“Watt hours” just means that you can run 1 device that uses 840 watts, for a single hour. Or you can use 420 watts for 2 hours. Or 210 watts for 4 hours, and so on.

So lets say you are running only a 40 watt laptop. All you have to do is divide 40 into 840 to find out how many hours your laptop will last on your lead acid batteries.

    840 / 40 = 21 hours

Obviously now your deep cycle batteries are stone cold dead, which you might not want to do, but with a deep cycle battery it will not be as bad for it as it would be if you had a standard lead-acid battery.

In the example of your laptop, you will also lose some of your power in the conversion process from DC to AC and back to DC again, probably around 20% total, bringing your total run time to roughly 16.8 hours. So it’s a good idea to be conservative when estimating operating time. Every time I convert DC to AC or AC to DC, I estimate 10% power loss in the conversion process. This power loss turns into heat which is why your AC/DC converters get hot.



In this series I discuss yield in weight of dried goods vs fresh, and effective cost per pound.

Yield of Dehydrated Bananas


Based on my real world measurements, 1 pound (454 grams) of fresh bananas purchased in the grocery store should yield 2.6 ounces (75 grams) of dried bananas.

Expressed as a percent, your bananas will shrink to 16.6% of their original size. Expressed as a fraction, 1/6.

Note that I include the peel in all of these calculations, for the simple reason that you pay for the peel at the grocery store.

Peels have a number of uses I won’t discuss at length here. They can be left on the bananas for longer and their sugars with leach into the bananas, and they can be composted.


Four bananas were used for this measurement. Bananas were weighed three times.

Once with peels,


Once without peels,peeled-bananas-weight

And once after drying was concluded. Bananas were dried for 15 hours and had chewy, leathery texture.


Your final dried weight will vary slightly based on level of ripeness and final dryness.

Effective Cost of Dried Bananas

Since dried bananas are shrunk into 1/6 of their original weight, finding the effective cost of dried bananas is as simple as multiplying the price of bananas at your local grocery store by 6.

For example, if bananas cost 69 cents per pound, your effective cost of dried bananas is $4.14 per pound. You can compare this cost with the cost of dried bananas at your local supermarket.

Note: Your true cost will be slightly higher based on the wattage of your dehydrator. Lets say I dried exactly 2 pounds of bananas for 15 hours using my 500 watt dehydrator. That means I used in total 7.5 amp hours at 8 cents per amp hour for a total electricity cost of 60 cents, or 30 cents per pound. This figure can be cut in half by drying 4 pounds instead of 2, by the way.