 | Home > Technical > How smart (or dumb) is the battery charging regime? |
 
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| BJH Member Since: 14 Apr 2022 Location: West Wales Posts: 17   
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Nice! Thanks for sharing your setup. OK, maybe I am overthinking the charging requirements after all.
Yeah 6 years is absolutely reasonable. Even if you allow £200 for the battery that's just £33 per year equivalent. Next to nothing, basically.
Cheers. |
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17th Apr 2022 12:09pm |
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| BJH Member Since: 14 Apr 2022 Location: West Wales Posts: 17
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Lovely - thanks for sharing. I love your roof tent setup as well. If I could go back this is the type I would get too. Mine is one of the more typical roof tents that fold out over the edge of the vehicle. Cheaper, but in the UK it can be a problem to simply park up somewhere and camp for the night. I think having the tent's footprint contained to the vehicle itself greatly reduces the negative attention that is drawn.
Yes see this is an area where I can really use input from an exerienced user of an aux system. My crude calculations went as follows: 1. Found a suitable fridge on the internet. Noted it is rated as 45W. 2. 45W * 24 = 1080Wh capacity required. 3. 1080Wh / 12V = 90Ah battery required. But factor in 50% discharge: 180Ah battery required. But what this doesn't factor in is the fridge in practice will cycle on and off. So it won't consume 45W continuously. This is something I had not considered.
Well that's plenty for me. I am primarily looking at off-grid for 24 hours. But 48 is the most I tend to do in the Land Rover. Thanks for the info  |
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17th Apr 2022 12:19pm |
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or a very inefficient one. Our Engel is spec'ed at 30W (2.5A @ 12.0V) but it's running for only 30 secs every 5 minutes or so. Of course that depends on how cold you want it to be and how hot it is outside.| macfrank Member Since: 05 Nov 2015 Location: somewhere in the north Posts: 1081  
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17th Apr 2022 2:21pm |
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| macfrank Member Since: 05 Nov 2015 Location: somewhere in the north Posts: 1081
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Now, after a holiday in southern France I took note of how long the Engel was actually running at various temperatures and settings: temp. | dial | on/off minutes | duty | mean Amps (calculated) 28°C | 2 | 4:30 / 2:45 | 62% | 1.6A 27°C | 1,5 | 3:15 / 5:00 | 39% | 1.0A 18°C | 1,5 | 2:00 / 12:35 | 14% | 0.4A So my estimate of "30 secs every 5 minutes" was probably at night, when it's usually on "1" or when camping in our own colder climate 
But it's also interesting to see that even when it's hot and the fridge on "2" (= results in very cold lemonade ), it's still not running all the time. In this example it would consume less than 40Ah in 24 hrs, which a 100Ah leisure battery should be able to provide. |
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8th Jun 2022 8:35pm |
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| BJH Member Since: 14 Apr 2022 Location: West Wales Posts: 17
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Thanks very much indeed for the information! Very useful.
28°C would be an exception around here. 18°C, is probably more typical, even on a Summer's day. So your experiment at hot temperatures with cold fridge setting is definitely a worst-case scenario, especially as you calculated it as if the high temperature would continue for the full 24 hour period, when in practice the night (even if only 5-6 hours at height of Summer) would offer a cooler period. So it seems to me that a 48 hour period is do-able on that setup in most conditions that I am likely to encounter. Thanks once again for taking the time to gather the data! My Aux Battery setup is continuing, albeit slowly. Got most of the equipment now but I'm still planning out all the fuse boxes, where the wires will go, how much wire I'll need at what gauges of wire, etc. I don't have the fridge yet though, will research that last. |
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8th Jun 2022 9:18pm |
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| steveww Member Since: 05 Jan 2022 Location: Uppingham Posts: 569 
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An alternative approach that I use for camping is a Jackery power pack.
https://www.jackery.com/products/jackery-e...-generator It has the battery, charging circuit, 12V, USB and mains inverter all in one neat package. When driving it's topped up via 12V from the vehicle. When camping the solar cell charges faster than fridge, phones, etc can discharge it. The only modification I did to my Defender was to add an extra 12V output in the boot. When I'm not camping I'm not carrying around an extra battery. |
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9th Jun 2022 10:39am |
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| sako243 Member Since: 08 Jul 2014 Location: Wales Posts: 1221  
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One important note everybody usually fails to grasp - you CANNOT apply/push current into something. It is the device itself accepting charge, for constant current there is a supervisory circuit that is limiting the current allowed to flow but if the demand for that charge falls off it can't increase it.
Why is this important? It is the battery dictating how much current is being requested from the alternator. The other important thing to note is that alternators do not "increase their output current" with engine speed. When an engine accelerates the voltage output by the alternator increases but the regulator is able to bring this back down to suitable levels. An alternator has an inherent maximum design current it can output (usually way less than a battery can accept) thus its inherently current limited by design. More modern alternators are smarter but usually for efficiency reasons rather than charge profiles (controlled via an ECU to limit charging until it is more fuel efficient to do so). Lead acid batteries are pretty damn resilient so as long as they are charged it doesn't really matter. If they get to the point of being massively discharged then that chemically alters the internal plates and you actually need a much higher voltage to "blow" off the sulphates that have formed on the plates. Greatly simplified points but the end result is the battery (until its knackered) simply doesn't care. Lead acids are pretty bomb proof. Ed 82 Hotspur Sandringham 6x6 95 Defender 110 300Tdi |
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10th Jun 2022 4:43pm |
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