More powerful batteries to make steam?

I noticed Lidl had 4Ah 20volt batteries a week or two ago and just wondered

Could these more powerful modern units start to be used for short steam runs of 5 to 10 minutes in a model boat or train with a decent small electric element?

The battery industry is really pushing the envelope at the moment

Check out the energy density of different technologies and you will understand why chemical energy (petrol, coal etc) is so much better than battery storage. It's true that battery technology has moved forward a lot in recent years but it starts from a disadvantage of an order of magnitude or more.

You could achieve a limited run quite possibly but look at the Isle of Man TT as an example of the relative range possible with motorbikes using the different technologies.

At least with electric heaters, the efficiency of the final stage of conversion is very close to 100%.

Murray

You might get a few more puffs if you stick a couple of LiPo batteries in there a pair of 11.1 V 8.4Ah should get you going better than the Lidl offering. I suspect most People would bypass the boiler and steam engine and drop a brushless motor in there to go with the battery.

Probably best to preheat the water with a larger land battery (car 12V) and then swap over to a smaller one for actual running.

Yes, preheating would save an awful lot of energy at the start of a run, boiling up with a camping gaz stove

Which would lead you to think "why not simply plug a small gas cylinder into the unit to start with"

Although an electric unit would be safer than a hot fire on a model boat for displaying steam

Edited By Ady1 on 30/09/2018 08:07:11

Oil refineries used to run steam trains that didn't have any boilers. They used to charge the steam chest with superheated very high pressure steam from a piped system and the boiler house was a couple of miles away.

A few calculations shows it's impractical.
Firstly the battery rating is misleading. 20V is the off load fully charged voltage, not the rate voltage which is 18V. (Dewalt tools in the USA are "20V" but the same tool in Europe is 18" due to consumer laws.) So using the correct rating 18V x 4Ah = 72Wh a watt is one joule per second so thats 72 x 3600 = 259.2kJ (about the same as 6g of coal) Specfic heat of water is 4.186j/g or 4.186kJ/l so our battery will raise 1 litre of water 61.9 degrees or from 20 to 81.9 degrees (at ses level ambint pressure)

Even if you start off at boiling, the heat of vaporization of water iss 2261kJ/kg so a fresh battery will boil away 115ml of water.

Robert.

For a boiler producing enough steam for a small engine I think the minimum requirement would be 500 to 1000W.

Before I converted my model boat to Stirling Engine it had a small pot boiler and a little V twin wobbler, and when I took it to the local pond I filled a Thermos with hot water, just to get steam up quickly.

Ian S C

Sounds like introducing another stage in the process with an efficiency of less than 100%.

Would probably work, but not as well as applying heat to the water directly.

Howard

I got shot down in flames recently for suggesting a mains powered steam boiler for efficiency testing. My idea was that it's easy to measure electrical input power accurately, and - for several reasons - difficult to measure the heat value of coal. Not just the calorific value of the coal, but the performance of the fire in a steam locomotive firebox is highly variable. (Enough air? Too much air? Tubes, blast, etc. etc.)

Trouble is I hadn't done the sums! Even with 24kW of mains power, the energy concentration is low.

If you're going to use batteries for propulsion an electric motor is the way to go, not steam. Not only is the conversion efficiency of electric motors high, energy is only consumed when needed and regenerative braking will recover a proportion of it. What energy the battery has is used very effectively. In comparison, steam and IC engines both waste energy by the bucketful when idling, and clutches, gearboxes and valve gear all snaffle energy from the output.

For short range driving electric cars have multiple advantages. They are brilliant in cities, not least because they accelerate so well from a standing stop. But if you need to travel more than 200 miles the ability to refuel quickly makes IC the best choice, at least for the moment.

Good idea to keep an eye on Li-ion opportunities. I noticed Screwfix had a 4Ah cordless drill with a brushless motor for under £90 last week. Cannibalising one could be a useful way of powering a model.

Dave

I'm pretty sure a wallpaper stripper would work fine for testing unloaded model steam engines. I think the pressure caps are rated 4psi, enough to turn most small models but not more.

But they use a lot of electricity compared to what a compact battery can deliver.

N.

I think I might have been the gunner when SOD got shot down, but back in the 1920s/30s there was an article in ME about a mains heated boiler. Heat was generated by passing electricity through the water. They just connected neutral to the shell and had a big insulated electrode inside connected to live. You could actually make a safe version of this if you had a big enough transformer to get the volts down to something non lethal. You could then ground the neutral. This would generate enough steam for a little stationary engine. It has a built in safety feature, if you let the water run down, there is no path for the electricity, so it doesn't overheat. You have to use AC so you don't electrolyse the water

I think the pressure cap is fitted as a last resort in case the steam outlet got blocked. In normal use the boiler/heater generates very little pressure, probably only slightly above ambient but obviously enough to induce the steam to travel along the large bore outlet hose.

If the boiler output was restricted by being connected to an engine the pressure would build up and possibly move the piston but I suspect it would not be able to generate steam fast enough to keep the crankshaft turning. That's what I think anyway as I have no live steam experience.

Ian P

AC still electrolyses the water, it just swaps the anode and catode around so you don't erode the anode.
It's not unsafe s long as the case is well grounded. Early designs of electric water heares and showers had a bare resistance element immesed in the water.

Robert.

A typical electric jug element is around 2.4 kW, at least where I am. That is 10 Amps from a 240V outlet. So given that the heater itself is 100% efficient, how big a model engine will that power? Well, IMLEC tells us that model locos achieve an overall efficiency of around 2% at best. Granted, some of the losses are up the chimney and from the outside of the boiler shell, so an electric boiler should do a bit better...but even if we get optimistic and assume that we can get 10% efficiency from our electric version, we are only going to get 240 Watts out of the engine. That's about 1/3 of a horsepower, which suggests to me that such an electric boiler might run something like a Stuart Number 1 OK, but would struggle with anything bigger.

You might think that since (almost) all the heat from the input ends up in the steam that the whole 2.4 kW should be available at the steam engine. Actually this is not the case. Even if the engine was an ideal heat engine using the Carnot cycle, the maximum efficiency would be 11- (Tcold/Thot), multiplied by 100 to express as a percent. With steam at 100 psig, the Thot temperature will be close enough 10 170 degrees, C and exhausting steam to atmosphere means that the Tcold temperature will be 100 degrees C or maybe even a little more. This gives a maximum efficiency of 16 %....for an ideal Carnot cycle heat engine operating between the temperatures that are practical for a model plant. Actually the Rankine cycle that we use is not an ideal Carnot cycle, since for a start all of the latent heat is thrown away, so we will never see a figure as high as 16% at IMLEC. (Absolute temperatures must be used forthe formulae, eg add 273 degrees to the Celsius figure)

We can improve the efficiency in two simple ways. One is to lower the cold temperature and the other is to raise the hot temperature. A condenser would enable us to get the cold end down to about 25 degrees, say 300 K close enough. Raising the pressure would also raise the hot end temperature, but most model plant is not allowed to go over 100 psig, unless you go to a flash steam boiler. The remaining approach is to superheat the steam, the limit here being what the materials and lubricant will stand.

So the tl:dr version...an electric boiler run from the mains will probably serve quite well for trying out typical Stuart size model; engines. Not really practical with a battery for a locomotive.

I'm sure you're correct, but I'm confused (no change there then) If the water is still electrolysed by AC, then it is split into hydrogen and oxygen. This sounds like a recipe for a bomb unless there is a divider beween the anode and cathode extending below water level, which you cannot acheve with AC. According to

**LINK**

it is all down to current density, keep it low and the gasses recombine as they are created. I'm still not going to make such a boiler

And then there are those super capacitors

**LINK**

https://www.youtube.com/watch?v=weRVZg_DEDs&t=0s&list=UUmHvGf00GDuPYG9DZqQKd9A&index=58

Sam

Interesting point (re 'bomb'.

I have a small Microflame jewelers' blowtorch that electrolyses distilled water to fuel it. From what I can see it delivers a mixture of hydrogen and oxygen from the electrolysis tank bubbled through a robust secondary storage / pressure tank (part filled with either Isopropyl Alcohol or Acetone) and has a flash arrestor in the torch handle. I think it relies upon the push fit rubber hose as a safety valve and relatively small volume to prevent major explosion.

The nozzle is a hypodermic needle and yes, when it blows back it can be exciting - the needle gets blown clean off and doesn't need to be pointing towards anybody! On more than one occasion the needle has hit the far wall of the workshop. (great bit of kit for fine work though with very focussed, intense flame)

The start of a flashback can be anticipated as the needle glows red hot and the hot bit creeps back along the needle with a hissing sound until there is a cloud 'crack' and the needle goes flying. At least the needle will be sterile!

More to the point, I have to presume that even a 'perfect mix' of hydrogen and oxygen requires a source of heat to initiate explosion.

It was Hot Point that made mains powered toy steam engines, my mate Mac has one in his little museum, I don't know if it is working, it probably needs new electrodes.

Ian S C

Another way of looking at electric vs coal as a way of raising steam is to estimate the number of watts output by the firebox of a real model engine. IMLEC provides measurements.

Coal has a heat value of between 15000 and 30000 kilojoules per kilogram, and I assume IMLEC would use the best coal available - 30000kJ/kg

A Joule is 1 watt per second.

Using Run 13 from IMLEC results in ME 4595, I see Marcus Peel's engine Springbok burnt 1.19lb of coal in 32 minutes. Conveniently, 1.19lb of coal is about 0.5kg, so:

watts = coalConsumed * heatValue * 1000(J) / runtime(S)

watts = 0.5 * 30000000 / 1920 = 7812W

As my learned friend Mr Duncan Webster and several others have pointed out I am not good at maths! However, I reckon the coal burning in Springbok's firebox averaged an output of nearly 8kW. (It could be replicated by three and a half British Standard electric kettles!)

Applying a sanity check, IMLEC calculated Springbok's efficiency at 1.889%, which I call 2%. That makes the power output of the engine about 160W which seems reasonable.

Hope that makes sense. If not where did I go wrong? (Ducks for cover!)

Dave