Automating a Grid powered pre-heater.

[Roger Crier]

I have bought a small pre heater from Germany, for use in the UK. It is called the Hot Frog and is made by Schwalm KG Motor Vorheizer Hot Frog engine preheater Hot Frog. (If your German is a bit lacking, click the "universal heizer" option, then, in the 4th paragraph, click the "mehr" link.) It is rated at 1200W and has an integral pump, thermostats and heating element in a very small neat package, and at £90 is half the price of a Kenlowe unit.
While the voltages on this particular unit are incorrect for the USA, the fitting procedure will be the same for any similar unit sourced in the USA, so this thread should be useful for all, especialy if the modifications to automate the pre heater can be implemented.

The unit is designed to simply be fitted in the coolant pipe that supplies the heater matrix in the climate control/ heater unit, and be plugged into mains power via perhaps a timer and an earth leakage circuit breaker, so no passers by get electrocuted. This means that on the Insight, the heater control valve that is also in this pipe, needs to be opened whenever the pre heater is used, by putting the temperature knob to max on the climate control, so there is a flow of coolant. This is where the fun/complications may start, as you have to either remember to set the Climate control's temperature control knob to "max" whenever you are going to use the "Frog", or rig up a switch on the heater valve that stops the frog powering up if the valve is shut, so that it is "interlocked" with the valve, and is always safe to use, even when you have been a dork and forgotten to open the valve etc.

Alternatively, we need to get cleverer, hack into the climate control, and have all the required parameters automatically synchronised to our requirements whenever the Frog is powered, by arranging things so Hot Frog sends appropriate voltages and earth connections
into the Climate control system using a dedicated control system.

Looking at the shop manual, the motors we need to "shift" within the climate control/heater system, seem to move if they are provided with power and then have various pins earthed, so it should be quite feasible to have the recirculation control motor set to recirculate, the Air mix control motor set to "max" (so the coolant valve is open) and the Mode control motor set to "screen" so matrix heat goes and de ices the screen. The plan would then be to run the Frog for about 40 minutes to warm all the coolant to 80 degrees or so, and then run the climate control blower for the last few minutes before your journey is due to start, so the car interior is nice and warm and the windshield is de iced. all the above can be set manualy before you turn the ignition off, but I am forgetfull, and thats where this automation comes into it's own.

I am not fully familiar with these insight motors, as all the control motors I have seen so far (on other makes of climate controls) are of the stepper motor type. Is there anyone out there who is fully familiar with the system we have and can verify my theory, or shoot it down in flames, as I am only going by the test procedures in the Shop manual. The motors vary slightly, so you cannot just pile in and stick voltages wherever you fancy or the motors will be wrecked. While the Air mix motor seems to be ok with a polarity reversal as part of it's functioning, the Recurculate motor and Mode control motor most certainly will be damaged by polarity reversal!!! The Mode control motor has more steps to it's function, and may need to be stepped through its positions before it gets where we want it to be, and the Blower motor is a normal everyday motor and just need powering up the correct way when it is wanted.
There are no procedures in the manual for setting the motors in any particular position when they have been replaced, so I am assuming, that once normal ignition power is given to the circuitry (once we have disconnected the Hot Frog derived power) all the motors will return to wherever the climate control decides to send them! IE back to wherever they were before we fiddled with them.

Anyone care to comment?

[retepsnikrep]

Roger and I have been discussing this via e-mail, but I have badgered him to post it on here so we can all contribute!

Roger has the possibility of charging at work in the future so he can use this system on both parts of his journey to maximum effect, combined with a small grid charger the hot frog insight toping up at work should give some impressive mpg figures!!

I looked at the schematic and believe that blk/yel wire from ignition switch via fuse no 16 (7.5A) Page 21/52 is the key.

A changeover relay at this point to allow the supply of 12v to the heater climate control unit independantly of the ignition may be doable. Driver sets climate control before leaving car for night, and when hot frog timer kicks in overnight prior to journey, climate control is also powered and does all reqd puffing hot air round car etc.

A simple fail safe sensor on the heater water valve so that hot frog is disabled should driver forget to leave climate controls set or if it shuts due to some other problem may do the trick.

Now before you all throw your hands up in horror I feel a Picaxe project comming on, controlling the frog and the climate control power relay.

A couple of sensors, one simple reed switch on water valve, and a temp sensor on frog body should sort it. Over to you Roger.

I don't think accesing/driving the individual motors/sensors in climate control is very viable. Just set heater/climate system before you leave and then power it up with hot frog. If you forget you will be punished by a cold car and ice scrapping duties, you won't do that very often i bet!

[richardh]

Hi Pete, Roger,

Getting up at 5:30am to drive 75 miles in the freezing cold, not in the fancy Audi with its deisel powered webasto cabin heater, means I am going to need one of these modifications.

Let me know if I can help in any way...

Richard

[retepsnikrep]

OK Roger

I knocked this up last Night at work, seems to simulate OK.

www.solarvan.co.uk/insight/HotFrog170209.txt

It provides the basic functions and probably costs less than a fiver.

A simple elapsed timer could be added to measure time since module was powered up to delay powering up of climate control which could be controlled by another relay.

[Roger Crier]

I fitted the Hot Frog to my Insight last night. I powered it up and watched over it as it as it warmed up the coolant and found that after 22 minutes, the temperature in the hot frog reached it's 80 degree C limit and it switched off both it's pump and it's heating element. Here is how it went in five minute segments.

Coolant temperature. Elapsed time.

66 0 ON
83 5
95 10
116 15
134 20 OFF at 22 mins
137 25
139 30
146 35
139 40 ON at 36 mins then OFF at 38 mins etc etc
139 45 Stopped test

While this is roughly what it is supposed to do, it does mean that with no flow of coolant, because it's pump is switched off, it will be "pants" from then on as a heating circuit! Assuming the designers knew what they were doing, the implication is that the Insight heater matrix and control valve provide a tad more resistance than they expect a car to have, so the frog gets too hot too quickly.

It would make far more sense if the thermostat (or even better, the picaxe controlled DS18B20 temperature sensor) only switched off the heating element rather than both the pump and element when the frog hit it's max temperature,.Keeping the pump running would get the frog cooled down much faster and it could then get on with further heating. Luckily this is easy to arrange as all parts of the Frog are independent, so I will re-wire it soon, so the pump stays running, and see what sort of figures it produces. They should be much better than the ones above.

At the moment, if the fledgling, tentative, Picaxe prog was implemented, the above figures would switch the Frog off permanently after 22 minutes. It looks like there needs to be two temperature sensors, one sensing the coolant and one on the Frog. With the frog element set to switch off at say 90 and the coolant set to turn off the pump at 85. Then, the frog sensor switches off the element only momentarily, and the coolant sensor shuts the system down fully when 85 has been reached.

It will be interesting to see how hot the Frog gets if the car is left to heat itself up to the temperature the cars fan switches in at. You could reason that this is the temperature the frog should be allowed to get up to, then the coolant temp can be set higher and the overall temperature will get high enough to open the cars thermostat so the coolant in the radiator gets warmed up as well. We will see how this all pans out. I suspect that the majority of the fuel savings can be had by warming up the coolant to a temperature similar to the test temperatures above, while the gains in reduced engine wear will require the higher temperatures before they materialise. Where are all the scientists when you need them?

People at work are already bored with engine coolant circuits and associated discussion, so if there are no more posts by me on this subject, would someone come over to Gaydon and get me out of the big red steel container outside our shop, because that is probably where I have been incarcerated.

[retepsnikrep]

Roger

IMO you def do not want to heat up water enough to open thermostat.

Anything circulating to the radiator is just wasted energy.

Here is quick schematic with two relays for the Frog element & Climate unit, you can have a third instead of the led if you wish to control something else.

www.solarvan.co.uk/insight/HotFrogSchematic.jpg

I think you can have more than one temp sensor, but I'll have to check that.

The whole thing is controlled by your external mains timer which comes on 1hr before you leave for work or whatever, and powers the whole thing up. The pic then controls thing from there activating the heater blower etc 10 mins before you leave, and watching temps etc. It won't power the frog element unless valve open and it could switch it on/off if it starts to get hot.

You still have to leave the heater controls in position when you leave the car the night before. The pic just powers it up.

The software can just be tweaked to do what you want.

Peter

[Roger Crier]

I have just modified the Hot Frog so the thermostat only switches off the element and not the pump. I also put a neon indicator light in the thermostat circuit so I could see the element switching on and off, and time it.

Testing went better this time with the temperature going from 49 to 125 in 30 minutes. The 80 degree thermostat then kicked in with a cycle consisting of 15 seconds off and 45 seconds on, I.E. Power on 75% of the time. This slowed things down a bit and the temperature got to 141 in the next 20 minutes and stayed there (141 to 143) over the next 35 minutes, so a definite plateau had been reached. The thermostat cycle was now 17 seconds on and 26 seconds off. (thats on 40% of the time I think ) The radiator was still not seeing any heat in it's hoses, so I assume the engine had got to a point where it was dissipating the 480 watts of heat with it's block surface. The body of the frog was not getting anywhere near as hot as it had when it did not have the pump providing a constant flow of coolant.

So 49F/9.4c to 141C/60.5F in 50 minutes.

I now need to test things with the Frog plumbed into the pipe work so it by-passes the heater matrix and heater control valves. This will serve no other purpose other than seeing if they are forming a restriction to the Frogs pump that causes the Frog's thermostat to cut in too soon and too often. If this works better and allows the heat to rise faster and further then the frog will have to be placed in parallel with the matrix and control valve. There will have to be an additional valve in the frog branch to shut it when not in use and the control valve will now need to be shut when the Frog is in use. Or, one of those diverter valves thingymajigs must be procured..

Onwards and upwards.....

[Roger Crier]

I tested the Frog out again today, and it worked very well!

In the 18 minutes I had before I was due to leave, it warmed the coolant from a stone cold 58 to 143. The car then took 1 mile to get up to full working temperature of 195, so I am well chuffed. That's a successful real time test as far as I'm concerned. I will check out the timings again when we get the next cold snap.

At a conservative estimate, 4 pence worth of electricity was consumed, so good savings will be made on fuel! I think chasing higher temperatures than that, is as Pete said, largely un-necessary, and a wastefull exercise.

I am now NOT going to try to by pass the heater matrix, and am going to concentrate instead on detailing the fitting procedure and getting on with turning Pete's control circuitry into a reality of some sort.

[retepsnikrep]

Roger

Here's a new version of the Frog software to go with the schematic a few posts below.

www.solarvan.co.uk/insight/HotFrog210209.txt

Seems to simulate OK.

[Roger Crier]

There isn't much to report that has not already been covered, but it has been working fine for ages.....So to re-cap progress so far, I have fitted no fail safes into the system, so I have to make sure that I have set the temperature control knob to Max heat, and ensure that the Hot Frog is turned on only when it is required. Also, I always put something into the speedo binacle to remind me that the car is plugged in so I do not drive off and take half of the house wiring with me!


You turn Hot Frog on, ( which in my case involves a wall switch near the telly ) and 1/2 an hour to 45 mins later I have a car that registers 143 degrees f on the scangauge as soon as it locks on after ignition. In rough terms it looks like the electric costs about 10p and gives about a 20p saving in petrol. This is most dramatic if you do say 6 miles as a trip as the saving represents a bigger % saving on the short trip fuel bill, wheras in my case the 10p profit is much less in percentage terms, but is still there, at about 2.5%. In my opinion, to also use this as a car interior warming device and windscreen defrost as well, the element would have to be more powerfull than 1.4kW as well as incuring a more stringent set up on leaving the car. at present i have only to set the temp control to max hot and give the motor time to re position the water valve.



In this recent cold snap, the engine gets up to it's 195f max temp in about 2 miles instead of about 5. All figs are approximate, the most accurate being the ones I listed a while back during initial tests.



I use Hot Frog every time I can, even in high summer as the saving and wear reduction is still there to be had.