I have done some rough calculations of power consumption to see how long my battery (7Ahr capacity) might last with the solar panel recharging it. It looks very positive, but I have had to guess at the GPS power consumption. I can't find figures anywhere. Does anyone know the power consumption of a Garmin 72 GPS?

**Power consumption calculations**

Per day power usage on weekend sail (nominally sailing for a maximum of 5 hrs per day)

Lighting: 2hrs/night at 80mA = 0.080A so 0.16Ahr per night

Depth: 5hrs/day at 22mA = 0.022A so 0.11Ahr per day

GPS: 5hrs/day at 100mA = 0.100A so 0.50Ahr per day (this is a guesstimate)

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Totals for a weekend cruise 0.77Ahr per day i.e. approx

**0.75Ahr/day**

Battery capacity (nominal) 7.0Ahr

Usable capacity say 50% 3.5Ahr

Therefor fully charged battery should run electrics for 4+ days with no further input.

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Solar Panel output 1.0W at 12V gives 0.08A (nominal)

Say 50% efficiency 0.5W at 12V gives 0.04A

Power generated for say 8 hours per day 0.32Ahr

Power per week (7 days) 2.20Ahr

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Therefor one week's solar charging gives power needs for approx 3 days sailing.

Or

Solar panel halves discharge rate i.e. battery power available for about 9 days.

Or

after two days sailing, only 0.75Ahr discharged and recharge time approx 2 days.

Sooooo....

If I sail at most three days per week (if only, I have a day job), the solar panel and battery should cover all needs for the season.

If I go for a week's cruise to the English RAID, I should have plenty of capacity, but it will take over a week to recharge the system. That shouldn't be a problem, I think I will want at least a week off after that.

Interesting to see how it will work out in practice.

I have an old Garmin GPS45 and the spec states

ReplyDeleteInput 4AAbatteries or 5-40vDC

Usage .75 watts

Battery life 10 hrs normal mode and up to 20hrs in battery saver mode

The old models were power hungry and I think they have improved but its the display that takes the power. I dont think you are far out with your estimate of .100A

Thanks Roger. If that is right I think I might have more reserve than I calculated. If it is 0.75W at 12volts, I make that about 0.06A.

ReplyDeleteI fitted one of the LED units this evening and I am astounded by how well it works. I will fit the other tomorrow evening. The colour of the light is meant to be "warm white" which means it is a bit yellowish. But nicer than the fierce blue-white you get from some LEDs.

Julian I assume that the .75 watts would be the draw on the batteries which would be about 5 volts so your original calculation would be about right. However I have given the data straight from the manual so you can place your own interpretation on it.

ReplyDeleteI run my GPS72 on batteries rather than "mains" - so why not do the same and just take it out of the power equation?? They only use a couple of AA's and I easily get 8-10 hours on that.. batteries cost peanuts, I get them from B&Q in big multipacks and keep a half dozen on the boat for spares/emergencies... do like the idea of your LED's though....

ReplyDeleteI find the AA batteries always run flat just when I need them. And peanuts add up. But mainly I needed to wire in the depth sounder and I had a battery tank so it seemed to make sense to wire in everything. I can still use AAs if the main battery conks out.

ReplyDelete