How to control the speed of a 24vdc pump from circulating water temperature?

[cygnusv]

One of the benefits of PWM motor control vs older variable (analog) voltage control is that it nearly eliminates loss of torque at low RPM.

Chris

This does attract me very much. Add to this the fact that the whole thing, with the exception of the vented enclosure is ready to go. My belt and braces position is that because I can still operate the PWM manually if required, I can test it 'live' on the system once the pump is fitted. Also the enclosure will be accessible.

I'm going to try it and report back. If it needs tweaking a bit I'll be bugging you all again for further advice.

Stu

PS
Just for clarification to Sunnysky's point (#79). The boiler I'm using has NO controls other than my own control of the air-screw. The heat output of the stove is not so much that I can't set the air screw at night (or during the day if we're going out) and leave it to pootle along without fear of overheating.

Thanks again all.

 

[Sunnysky]

I am curious about the pump's hysteresis for %pwm for
1) start
2) stop
3) min needed for acceptable quiet and adequate flow when max heat flow is desired
4) any resonant acoustic speeds in between.

 

[CDRIVE]

Stu is a seaman not an EE or ET. It's doubtful that he's even an electronics enthusiast. IMHO your questions should reflect this.

Stu, if you find that change in water temp vs the change in motor speed (< >) is too fast for your liking a large Cap in parallel with the .1uF Cap will slow any rapid change in Thermistor (R) or Pot (R) setting.

Chris

 

[hevans1944]

@cygnusv and @CDRIVE: I've been lurking here, watching you two make progress on this project, with @Alec_t and @shrtrnd chiming in occasionally. Now that Stu is almost ready for "sea trials" I am curious about a few things... my wife and I will be moving to Florida, and one possibility is to purchase a "houseboat" and pay marina fees. Neither of us are sailors, and we don't have any experience living on the water, so this may be an unwise consideration compared to a nice (hopefully) dry house on (mostly) dry land.

Here are my questions: How big is the boat the two of you live on? Is it a flat-bottomed "houseboat" or a conventional watercraft with keel, transom, rudder, cabin, engine, etc.? Do you leave it moored or venture away from the dock on excursions? What kind of "multi-fuel" heater does it have? Is this a "fireplace" kind of heater that burns wood, coal, charcoal briquets, etc.? Or does it burn propane, liquefied natural gas (LNG), or a liquid fuel such as diesel fuel? What is the BTU per hour rated output of the stove? Do you use the stove for cooking?

Years ago, my maternal grandmother had a huge cast iron stove in her kitchen that mostly burned coal but was lighted with wood. It had removable flat, round, plates on the top for cooking and lighting the stove, a water tank on the side for heating cooking water, and an oven for baking. When the stove was fully stoked with hard coal and doing its thing it produced enough heat to keep the kitchen and an adjacent sewing/dining room toasty warm in the middle of a West Virginia winter. There was also a "pot belly" stove in the middle of the living room that was fired up with coal on really cold days, and a tea kettle or coffee pot usually sat warming on top of this stove. And that's about the extent of my experience with wood and coal fueled stoves. I doubt either one would be suitable for use on a boat or at sea, so I am curious about sea-worthy stoves and how an air-to-water heat-exchanger for circulating hot water through a radiator might more efficiently heat the interior of the boat.

Landlubber Hop

 

[CDRIVE]

Hop, I could be wrong but I think USCG regulations will accept only Propane for cooking and heating. Though, possibly electric cooking & heating will pass muster.

On that note it's my personal opinion that land lubbers should first own quite a few holes in the water before considering living aboard one!

Since you're moving to Florida (I think we're all filled up) you should be made aware that many, if not most marinas do not permit live aboard. The ones that do are constantly under scrutiny and all out assault by the surrounding home owning community, though less so in fresh water communities.

A lifetime old salt...
Chris

 

[hevans1944]

<sigh> Well, it was just a thought... my wife and I sometimes travel to Cookeville TN from Dayton OH to visit her relatives there. On the way, we pass by a large fresh-water marina located below one of the TVA dams. We often see houseboats tied up there to a floating dock (which also contains a gift store and restaurant). Some of these boats have shore power cables and there have been incidents of swimmers being electrocuted after diving into the water near one of these boats. As Paul Stookey (of Peter, Paul and Mary fame) said on one of their albums: "Swimming is staying alive in the water." Best to avoid water with boats connected to shore power.

Florida can't possibly get "all filled up" because that's where old folks go to die. Since you can't take it with you, I am expecting some good deals on property if Donald Trump is elected President.

 

[cygnusv]

I am curious about the pump's hysteresis for %pwm for
1) start
2) stop
3) min needed for acceptable quiet and adequate flow when max heat flow is desired
4) any resonant acoustic speeds in between.

Hi Sunnysky
Chris answered this, accurately, in the next post. I must admit I had to look up the word 'hysteresis' prior to answering you!
Interesting though.
Stu

 

[cygnusv]

@cygnusv and @CDRIVE: I've been lurking here, watching you two make progress on this project, with @Alec_t and @shrtrnd chiming in occasionally. Now that Stu is almost ready for "sea trials" I am curious about a few things... my wife and I will be moving to Florida, and one possibility is to purchase a "houseboat" and pay marina fees. Neither of us are sailors, and we don't have any experience living on the water, so this may be an unwise consideration compared to a nice (hopefully) dry house on (mostly) dry land.

Here are my questions: How big is the boat the two of you live on? Is it a flat-bottomed "houseboat" or a conventional watercraft with keel, transom, rudder, cabin, engine, etc.? Do you leave it moored or venture away from the dock on excursions? What kind of "multi-fuel" heater does it have? Is this a "fireplace" kind of heater that burns wood, coal, charcoal briquets, etc.? Or does it burn propane, liquefied natural gas (LNG), or a liquid fuel such as diesel fuel? What is the BTU per hour rated output of the stove? Do you use the stove for cooking?

Years ago, my maternal grandmother had a huge cast iron stove in her kitchen that mostly burned coal but was lighted with wood. It had removable flat, round, plates on the top for cooking and lighting the stove, a water tank on the side for heating cooking water, and an oven for baking. When the stove was fully stoked with hard coal and doing its thing it produced enough heat to keep the kitchen and an adjacent sewing/dining room toasty warm in the middle of a West Virginia winter. There was also a "pot belly" stove in the middle of the living room that was fired up with coal on really cold days, and a tea kettle or coffee pot usually sat warming on top of this stove. And that's about the extent of my experience with wood and coal fueled stoves. I doubt either one would be suitable for use on a boat or at sea, so I am curious about sea-worthy stoves and how an air-to-water heat-exchanger for circulating hot water through a radiator might more efficiently heat the interior of the boat.

Landlubber Hop

Hello Hop, nice to talk

Our boat is our avatar, top left of this reply. She was built on the river Thames and launched in 1951. She is mahogany on oak and is stabilised with a cast iron keel, a 'proper' boat. The avatar picture was taken in 1972 while she was making a north sea crossing from Boston in Lincolnshire to Great Yarmouth. It is the only picture we have of her under sail. We still have the mast and sails etc but nowadays only use her under engine power.

The engine is the original Coventry CDB 30HP 4 cylinder engine she was built with - still in excellent condition.

She is small for a live aboard at 30 foot long with a 9' 6" beam. She draws about 3' 2" with the added weight of all our kit. The whole of the bow cabin is a huge double bed. Next to the front cabin opposite one another is our galley and toilet shower etc. Then we have the main cabin where we have a 'Boatman' stove that gives ( with a mode we made) up to 6KWs of heat. The covered wheelhouse (shown on the avatar) is a large space wih all the sailing and engine controls, a domestic freezer, 2 fridges, a microwave / oven and a full size washer/ dryer. Sounds a lot but it all fits snugly.

The waters we sail in, and where we moor are inland and generally quite sheltered. This allows us to use pretty standard equipment. Sea use would require a gimballed cooker and a complete rethink of heating on board.

Webasto and Eberspacher make stable diesel heaters and these are used on many boats for centrally heating the space with radiators or piping up as hot air variants.

We love our life afloat and would heartily recommend anyone to try it. Why not rent a boat for a week or two first though, before committing?

Stu

 

[hevans1944]

Why not rent a boat for a week or two first though, before committing?

Excellent idea! We plan to stay with my daughter and her husband in Sarasota when we visit Florida to inspect properties later this summer. Shouldn't be very many snowbirds cluttering up the state and jacking up prices in August or early September, so maybe we can find a boat rental at a reasonable cost. I will certainly investigate that option, especially if we need an extended stay. It is so easy to "wear out your welcome" when staying with relatives, and I sure don't want to do that!

 

[cygnusv]

Excellent idea! We plan to stay with my daughter and her husband in Sarasota when we visit Florida to inspect properties later this summer. Shouldn't be very many snowbirds cluttering up the state and jacking up prices in August or early September, so maybe we can find a boat rental at a reasonable cost. I will certainly investigate that option, especially if we need an extended stay. It is so easy to "wear out your welcome" when staying with relatives, and I sure don't want to do that!

We're not currently able to trade up but...., Kath and myself (and our 2 cats) would be very comfortable indeed with something between 40 and 50 feet. We would require a beam (width) of around 12'6" minimum. It's amazing how easy it is to adapt. Here in the UK the cost difference (and taxes) between having a boat or a house are VERY significant. Of course, at some point, some overpaid official will find a way to screw us over...... Hey Ho

Has 'Hevans'1944 got a Welsh connection?

Stu

 

[cygnusv]

Hello again everyone

Although we're not ready yet to fully report, I am very happy to say that yesterday we fired the system up and it worked!
Before I report fully there are still issues that will affect the heating system use..

There is no insulation fitted yet, so a huge amount of uncontrolled heat loss at the moment.
I intend to fit a pipe stat so that the pump does not run until the temperature of the water leaving the boiler is above 50 degrees celsius. I have a question about this below.
The radiator in the front of the boat has a TRV fitted, but the towel rail in the bathroom does not. I'm going to change this and fit a TRV because it will balance the heat available for the rest of the system.

When we fired up the boiler it was to test for leaks and to 'cure' the fire cement in the stove. Also it is very warm at present so we could only use tickover water temperature, Proper testing will begin when autumn gets a grip in a few weeks time. I'll report back fully then.

In the meantime. I mentioned above that I want to fit a second pipe stat to prevent the pump running at low temperature. (The other pipe stat is connected to a zone valve and operating on AC current) The pump is 24 volt DC less than 1amp current. Will a standard central heating pipe stat deal with low amperage DC current? I guess they are designed for AC circuits. Any thoughts?

Thanks again, Stu

 

[Alec_t]

Have you asked the makers of your particular pipe stat? They should know what the DC contact ratings are.

 

[CDRIVE]

Stu, Winter is just a few months away for me too. It's a bummer but I may have to wear a shirt on some of those days!
Chris

 

[cygnusv]

Stu, Winter is just a few months away for me too. It's a bummer but I may have to wear a shirt on some of those days!
Chris

Har bloody har! I'm jealous! Lucky you. Though of course, you get more hurricanes than we do!

Okay update.

Very happy so far. Having sorted the odd leak out everything appears to be working well. The only questionable thing was 'is the thermistor working?'. The question was answered, by chance, last night in the early hours.

It was quite chilly outside, so the fire was lit. By intent, the first radiator in the system is meant to act as a gravity rad so that if we lose power the system will still operate (hopefully) without boiling. Somehow I turned off the power to the pump and fell asleep. I woke up in the night and realised that the pipe feeding the gravity rad (which I sleep against), was very hot. No problem, i turned the power back on and the pump started at double the speed I'd set the pwm at. Fortunately I realised that maybe this was the thermistor doing its job. Within seconds the pump speed smoothly dropped as cool water was introduced. Thermistor working! This forum saved the day again. Thanks guys

A final question. Everything is working faultlessly as far as I can tell, but is it likely that the PWM will damage the motor because the motor is never going to run at its full design speed?

 

[CDRIVE]

I wouldn't loose sleep over it. PWM is the most effective control method for brushed motors. If your having sleepless nights over it you can always check it to see if it's abnormally hot. Doubt it though.

Chris

 

[hevans1944]

Has 'Hevans'1944 got a Welsh connection?

Probably. I was born in Welch, West (by God) Virginia. That's coal mining country. Don't think my grandfathers or grandmothers were immigrants, but some of my ancestors might have crossed the pond from Wales.

 

[CDRIVE]

Stu, It's always good to hear that advice given here at EP actually works!
Don't forget, if it gets too cold do like the song says and roast your Chestnuts on an open fire.

Chris

 

[Gandes]

PWM is good for this kind of motors, try to think about safety there like semiconductor diode applications i circuits

 

[CDRIVE]

PWM is good for this kind of motors, try to think about safety there like semiconductor diode applications i circuits

What's your point?

Chris