GB2455126A

GB2455126A - Vehicle water heater

Info

Publication number: GB2455126A
Application number: GB0723389A
Authority: GB
Inventors: Ian James
Original assignee: TRANSVEND Ltd
Current assignee: TRANSVEND Ltd
Priority date: 2007-11-29
Filing date: 2007-11-29
Publication date: 2009-06-03
Also published as: GB0723389D0

Abstract

The water heater 14 is configured for operation from a vehicle battery and includes a water tank 22, an electrical heating element and a switch means 26 operable to switch power to the heating element on and off. A low battery circuit is operable to detect when the voltage of the battery is below a first predetermined threshold value. It also prevents the supply of power to the heating element when the voltage is below the threshold. The low battery circuit may provide a visual 38 and/or audible signal when the voltage is below the predetermined threshold. A second predetermined threshold value for the voltage may also be provided in which the circuit permits the supply of power to the heating element following prevention thereof only once the second threshold is reached.

Description

A Water Heater The present invention relates to a water heater. More particularly, the present invention relates to a water heater configured for operation from a vehicle battery, which comprises a system for detecting a lowering of voltage in the batteiy and for suspending operation of the water heater in such a situation. The present invention also relates to a method of heating water in a water heater.

Various organisations, such as fire services, ambulance services, construction and maintenance companies and rescue organisations interpret current UK legislation to mean that the vehicle their mobile employees work from is their "place of work". Under this legislation it is a requirement that these mobile employees have the ability to make hot drinks when working remotely.

The present applicant provides a range of self-contained water heaters and dispensers that can be installed in a wide range of vehicles, from buses and fire tenders down to relatively small car-derived vans. Water heaters of this type rely on batteries for the power to heat water. Larger vehicles have space to mount additional 1 2V batteries that are dedicated to this purpose. However, on smaller vehicles (e.g. ambulances, crew vans for the construction industry), there often is not space for this, and the same battery is used for the heater and for the remainder of the vehicle's electrical needs (including starting the engine).

Water heaters of this type can also be distinguished from domestic heaters by the need to be built to operate at high currents (around 30A), a level which conventional control circuitry is unable to handle, and to withstand tough operating conditions.

The applicant has recognised that, in certain circumstances, there is a danger that the power drawn by such water heater may deplete the battery to the extent that insufficient power remains to start the vehicle or operate other ancillary equipment. Clearly this is undesirable, particularly in connection with vehicles used by emergency services.

The present invention seeks to overcome or at least mitigate the problems of the prior art.

One aspect of the invention provides a water heater configured for operation from a vehicle battery, the water heater comprising: a water tank; an electrical heating element: a switch means operable to switch power to the heating element on and off; and a low battery circuit operable to detect when the voltage of the battery is below a first predetermined threshold value and to prevent the supply of power to the heating element the heating element when the voltage is below the threshold Advantageously, the low battery circuit is operable to provide a visual and/or an audible signal when the voltage is below the predetermined threshold value.

Preferably. the low battery circuit has a second threshold value for the voltage which is higher than the first, and the circuit is configured to permit the supply of power to the heating element following prevention thereof only once the second threshold is reached.

Preferably, the water heater further comprises one or more components to smooth the supply of power to the low battery circuit and/or one or more components to protect the low battery circuit from an excess voltage and/or means to prevent the supply of power to the heating element in the event that the water tank is not filled to a predetermined level and/or a thermostat operable to prevent the supply of power to the heating element one a predetermined water temperature is reached and/or a switch operable to cause one cycle of heating until the predetermined water temperature is reached.

The low battery circuit preferably comprises means by which the first and/or second threshold voltages may be adjusted.

The low battery circuit is advantageously mounted within a housing of the water heater.

The water heater preferably further comprises mounting means for mounting the heater in a vehicle.

A second aspect of the present invention provides a method of heating water in a water heater according to the preceding paragraph, the method comprising the steps of: 1) adding water to the tank: 2) switching on a supply of power to the heating element; and 3) monitoring the supply of voltage to the water heater and switching off the supply of power to the heating element if the voltage drops below a first predetermined threshold value.

The method advantageously comprises the further step of monitoring the temperature the water and switching off power to the heater if a predetermined temperature is reached.

Following the switching off of power at step 3) the method preferably prevents the power being switched back on again until the voltage reaches a second predetermined threshold value, the second predetermined threshold value being higher than the first.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig. I is a perspective view of a vehicle incorporating a water heater of the present invention: Fig. 2 is a perspective view of the water heater of Fig. I: Fig. 3 is a wiring diagram for the heater of Fig. 2; Fig. 4 is a wiring diagram showing the voltage sensing unit of Fig. 3 in more detail: and Fig. 5 is a flowchart illustrating the operation of the water heater.

Fig. I illustrates a rear portion of a vehicle 10 having a loadspace 12 that incorporates a water heater 14 according an embodiment of the present invention. The primary function of the loadspace varies according to the purpose of the vehicle 10. For example, for a vehicle used in the construction industry the loadspace 12 may be used for storing tools and materials, for an ambulance, the space may include medical supplies and a stretcher.

In order to maximise the amount of space available to perform this primary function, it is important for the water heater to be compact. In addition, since the primary function often includes the loading and unloading of materials, it is important that the water heater is robust, in order to withstand knocks and possible contact with corrosive materials.

In alternative embodiments, the vehicle loadspace 12 may be converted specifically for the purpose of acting as an eating and drinking area for personnel (a "messing vehicle"), e.g. on building sites or for rail maintenance personnel.

Fig. 2 shows the water heater 14 in more detail. The heater comprises a substantially cuboid housing 16 of sheet metal (e.g. zinc galvanised steel with a powder coating) incorporating a mounting bracket 18 at the rear and an opening 20 at the top for filling a water tank 22. The water tank is preferably made from 316 grade stainless steel. The opening is closed using a cap (not shown) having a bayonet fitting and a handle. A push-type tap 24 is provided on the front of the heater 14 with a connection to the bottom of the tank so that water may be drained by gravity from the tank 22 when desired. The tank has a capacity of 2 litres in this embodiment. This can be varied according to user requirements, but will typically be within a range of I to 5 litres. A pivotally mounted cover (not shown) is, in some embodiments, provided over the tap to prevent the tap being accidentally actuated, and to protect it from contaminants.

On the lower front portion of the housing are an switch means in the form of an on/off switch 26, a push-to-heat switch 28 and lights (LEDs) indicating power on 30, heating 32, ready 34, low water 36 and low voltage 38. The power on light 30 is integral with the on/off switch 26. The heating light 32 is integral with the push-to-heat switch 28. In other embodiments lights 30 and 32 may be separate.

The water heater 14 is wired to the 1 2V DC (or in the case of larger vehicles, sometimes 24V DC) supply from the vehicle battery (not shown) via a heavy duty plug and socket under the heater (not shown). The supply is preferably fused.

A wiring circuit 15 for the heater 14 is shown diagrammatically in Fig. 3. Broken lines indicate which relay coils correspond to which relay contacts.

The wiring circuit 15 is preferably contained entirely within the water heater housing 16, so that installation of the heater can be quickly and easily achieved, with only a limited need to adapt the existing vehicle wiring.

The control portion of the wiring circuit 15 is energised by the bi-stable on/off switch 26 being closed. The power on light 30 is then illuminated, in series with the on/off switch is a float switch 40 (e.g. a magnetic reed switch) configured to close when a sufficient level of water within the tank 22 is reached. The float switch 40 has an associated relay coil 42, which when energised causes low water relay contact 44 to move to the position of Fig. 3 at which the low water light 36 is off. When in the alternate position (when the float switch 40 is open) the low water light 36 illuminates and the heater in inoperable.

A thermostat is 44 positioned to be able to measure the temperature of the water is also wired in series with the on/off switch 26 and is set such that up to a predetermined temperature, preferably below boiling point (e.g. 90°C) it is in the position illustrated (in contact with a "low temperature" contact), but at this temperature. switches to the other contact, causing the ready light 34 to illuminate. It is undesirable to allow the water to reach boiling point for safety reasons. The thermostat 44 is further configured to only switch back to the low temperature contact at a lower temperature, preferably 85°C.

The push-to-heat switch 28 is normally open and is connected to the low temperature contact of the thermostat 44. such that when closed an associated push-to-heat relay coil 46 is energised, which in turn moves a push-to-heat relay contact 48 from an open position to the illustrated closed position. The relay is configured to remain in this closed position until the thermostat trips out at 90°C, at which temperature it opens. In the closed position, the heating light 32 is illuminated and a heater relay coil 50 is energised.

This energising of the heater relay coil 50 closes heater relay contacts 52, causing current to flow through a heating element 54 and associated thermal fuses 56 in the tank 22. The thermal fuses 56 ensure that it is not possible for damage to be caused to the unit as a whole by the heating elements 54 overheating in the event of a malfunction in the control circuit.

A voltage sensor circuit 58 is also shown schematically in the wiring diagram of Fig. 3.

but is shown in more detail in Fig. 4. The circuit 58 comprises a first diode 62 to protect the circuit from a reversed battery connection and a first resistor 60 to protect the circuit from overvoltage (typically in excess of ISV on a 12V circuit) in conjunction with a second (transorb) diode 64. A capacitor 66 smoothes the DC power supply to the circuit.

and, together with the first resistor 60 softens the speed at which the voltage rises when the circuit is connected to the battery.

A third (zener) diode 68 acts as a shunt regulator such that a voltage sensor relay coil 70 is only energised when the supply voltage exceeds a predetermined value (e.g. I I.4V). In order to add hysteresis to the circuit a transistor 72 is arranged to act as a schmitt trigger.

This ensures that the circuit does not "tiutter" (i.e. if the voltage drops below the predetermined value, the relay coil 70 will not become re-energised until the supply voltage has risen significantly up to a second predetermined value, such as I 2V or higher).

The trigger and hysteresis thresholds are set by further resistors 74. 76, 78, 80, and variable resistor 82. A third diode 75 protects the circuit from voltage spike due to inductance in the relay coil 70.

When the supply voltage is above the predetermined value and the relay coil 70 is energised the relay contact 84 is in the alternate position from that of Fig. 4 and the remainder of the heater wiring circuit is operable. When the voltage drops below the predetermined value, the relay contact 84 switches to the Fig. 4 position and the low voltage light 38 flashes. In a preferred embodiment, an audible buzzer or the like (not shown) is also operable in conjunction with the low voltage light 38.

The water heater 14 may be positioned a variable distance away from the battery, and resistance in the supply wires will reduce the actual voltage at the input to the heater the further away from the battery the heater is located. Thus, for each installation it is desirable to adjust the threshold value to account for this, in order that the circuit is not cut-out at too high or at too low a voltage.

Fig. 5 illustrates the method of operation of the water heater in more detail. At step 110 a user switches the on/off switch 26 to "on". If the voltage sensor circuit 58 detects sufficient battery voltage, the power on light illuminates at step 111. If the voltage sensor circuit 58 detects a low battery voltage, light 38 flashes and the buzzer sounds at step 112 to alert the user to start the vehicle 10 engine to recharge the battery at step 114. As set out above, operation of the water heater is prevented until a predetermined suitable voltage is attained.

At step 116 if the tank 22 has not been filled to the minimum fill level, the low water light 36 will come on and the user must add water at step 118 for the light to be extinguished at step 120 and for heating to be possible. If the water is already at the predetermined temperature, the therniostat 44 will switch at step 122 to the contact at which the ready light 34 is illuminated and the user can then dispense water from the heater 14 at the correct temperature to make a drink at step 136. If the temperature is not reached, the ready light is not illuminated at step 124 and then the user presses the push-to-heat button at step 126, which at step 128 energises the heater relay coil 50, causing the heating elements 54 to heat the water and the heating light 32 to illuminate.

Whilst the water is being heated the low battery monitoring circuit 58 continues to operate, and if a drop in voltage to below the threshold is detected, then at step 130 power to the heating elements 54 is cut and the low battery light 38 flashes.

Assuming the voltage is sufficient, heating continues until, at step 132 the predetermined temperature is reached, the ready light 34 illuminates, the heating light 32 extinguishes and the user can make a hot drink at step 136.

It will be appreciated that numerous changes can be made within the scope of the present invention. A variant of the heater may omit the push-to-heat switch and simply cycle through heating and ready cycles for as long as the heater is switched on, there is sufficient water and sufficient voltage. However, such an arrangement would typically be undesirable for the type of vehicle in which the low battery monitoring circuit would be particularly applicable, in view of the likely increase in energy use.

Alternative arrangements for the low battery monitoring circuit may be used. For example, for high volume production it may be desirable to use an integrated circuit.

Alternative display and switching arrangements may be provided. For example the lights may be replaced by an LCD.

The construction and dimensions of the heater may be altered. For example, portions of the heater may be manufactured from plastics, and the mountings may be changed in order that the heater can be portable. Alternative taps may be provided or a solenoid valve with a switch can be used to dispense water. The water heater may be adapted to heat water for hand washing. In this variant, the heater would be set cut out at a lower temperature and the may be integrated with a basin.

Claims

Claims 1. A water heater configured for operation from a vehicle battery, the water heater comprising: awater tank; an electrical heating element; a switch means operable to switch power to the heating element on and off; and a low battery circuit operable to detect when the voltage of the battery is below a first predeterniined threshold value and to prevent the supply of power to the heating element when the voltage is below the threshold.
2. A water heater according to claim 1 wherein the low battery circuit is operable to provide a visual and/or an audible signal when the voltage is below the predetermined threshold value.
3. A water heater according to claim 1 or claim 2, wherein the low battery circuit has a second predetermined threshold value for the voltage which is higher than the first, and the circuit is configured to permit the supply of power to the heating element following prevention thereof only once the second threshold is reached.
4. A water heater according to any preceding claim further comprising one or more components to smooth the supply of power to the low battery circuit.
5. A water heater according to any preceding claim further comprising one or more components to protect the low battery circuit from an excess voltage.
6. A water heater according to any preceding claim wherein the low battery circuit comprises means by which the first and/or second threshold voltages may be adjusted.
7. A water heater according to any preceding claim, further comprising means to prevent the supply of power to the heating element in the event that the water tank is not filled to a predetermined level.
8. A water heater according to any preceding claim, further comprising a thermostat operable to prevent the supply of power to the heating element once a predetermined water temperature is reached.
9. A water heater according to claim 8, further comprising a switch operable to cause one cycle of heating until the predetermined water temperature is reached.
10. A waler heater according to any preceding claim wherein the low battery circuit is mounted within a housing of the water heater.
11. A water heater according to any preceding claim further comprising mounting means for mounting the heater in a vehicle.
12. A method of heating water in a water heater according to any preceding claim, the method comprising the steps of: 1) adding water to the tank: 2) switching on a supply of power to the heating element; and 3) monitoring the supply of voltage to the water heater and switching off the supply of power to the heating element if the voltage drops below a first predetermined threshold value.
13. A method according to claim 12 comprising the further step of monitoring the temperature of the water and switching off power to the heater if a predetermined temperature is reached.
14. A method according to claim 12 or 13 wherein following the switching off of power at step 3) the power can only be switched back on again once the voltage reaches a second predetermined threshold value, the second predetermined threshold value being higher than the first.
15. A water heater substantially as hereinbefore described and/or with reference to Figs. 1, 2, 3, 4, and/or 5 of the accompanying drawings.
16. A method substantially as hereinbefore described and/or with reference to Figs. 1, 2. 3. 4, and/or 5 of the accompanying drawings.