Monday, February 29, 2016

What is that fuzzy plug?

Yesterday I posted a slightly fuzzy photo of my new inlet in the side of the bus. Many of you will not have seen a connector such as that before. There's a reason for that - it's not sold in Lowes (hiss, spit) or Home Depot (cough). It is designated as a Nema 6-30I. 

The Nema designation means that it's an inlet (hence the I) and will handle 30A at 250v. Unlike the normal Nema connectors used in the US (Nema 5-15), this is a twist-lock connector. Now the twist lock means that when the connector is inserted, it can be twisted and locked into place. This has the upside that it won't fall out but the downside that it's easier to damage the inlet etc by simply tripping over the power cord.

On most RVs etc the connector used is the TT30 connector such as the connector I installed in m'lady's front yard. Here we get to the nitty-gritty! Hunting around I could not locate a TT30 inlet for less than $70. Thus I went for a different connector. It makes no realistic difference. It'll work just the same. The only difference is that if I have to replace the cord then I'll have to build my own cord like I have been. I can't use off-the-shelf cords.

The upside of off-the-shelf cords is that they're available at most RV outlets. The downside is that they're sold at huge prices. Cords are available secondhand (probably red hot too) but would you trust a cord of unknown capacity? I won't trust anything electrical or electronic that's secondhand. I've seen too many secondhand electrics and electronics bursting into flames.

A subsidiary upside of having a bespoke connection is that because it's non standard, it's not as desirable to those that would wish to steal cables. Now I'm not thinking of a masked bandit in a black and red striped sweater with a sack labelled "swag" over his shoulder but I am thinking of less scrupulous individuals that "forget" their RV cord and "borrow" somebody else's cord but never return it.

I can see a day when RVs will largely not have cables any more. Look at it like this - at $2.50 a foot for 30A cable - the cables are just ridiculously expensive. The standard RV cable is about 50 feet. That represents about $75 of investment just lying on the ground for somebody else to pick up and walk away with. If they figure they can get a bottle of beer out of it, they figure it's been a good day's work. Heavens I've even heard of people's house air-conditioners being stolen and they weigh up to a ton!

With the rising price of copper and the almost static cost of generators, there's going to be a convergence. It will soon be cheaper to slip a $300 generator under an RV than to put a power cord. I don't really see solar and wind power as being worthwhile.

Investigating solar power, to produce the 10A at 120v needed to power a microwave directly, I'd need 1200W of power. Solar panels are $1 per watt wich does not mean that I'd need $1200 of panels. Because of the poor light at times I'd most likely need $2500 of panels just to run the microwave directly at midday. 

Batteries seem like a good idea but the cheapest deep cycle battery gives 100ah of power which is a misnomer because you're only supposed to take a maximum of 55% out of a battery before the battery gets damaged. Thus a $90 100AH battery is about $2 per amp hour or 17c per watt hour. 

In order to run a microwave for 15 minutes (thinking about the lowest power microwave in Walmart that takes 15 minutes to cook a plate from frozen and which coincidentally rusts to bits in 2 years), 300 watt hours of power would be needed at 10A. Now those two factors are very important. Remembering the 10% power loss from using an inverter (and ignoring the $300 cost of a 2KW inverter), 100A at 12v would be needed for 15 minutes. Most 12v batteries can't discharge more than 20A for more than a few seconds without getting dangerously hot. To be safe, think about 10A. This means 10 batteries in parallel, each weighing 50lbs would be needed to power a microwave. That's 500lbs of battery.

How much would a system cost that could power a microwave? Well, $900 in batteries, $1200 in solar panels, $300 inverter plus whatever I haven't thought of. That's a minimum of $2400. Of course if you went for lithium batteries, you'd need less batteries and be carrying less weight but be paying 20 times more for the batteries. EG a 300ah lithium battery is about $3500 and has a maximum constant discharge of about 50A.

So, the cheapest form of cooking power is a plug-in for electrical operation. The cheapest plug is a Nema 6-30. But cheaper even than carrying a generator is a portable gas cooker with butane tanks just like you'd use for camping! 

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