Simple Hot Water Urn Schematic or Operation Explanation - Page 1
Forum section: electronics / beginners

author: edy
author_rank: Super Contributor
timestamp: March 02, 2017, 02:52:09 am
content: I am trying to understand a simple hot water urn and need to know how it works electrically and what certain buttons do. I found an instruction manual here and just trying to figure out different models and whether they are doing the same thing:http://www.confettipartyrentals.com/galleryupload/webdoc/guides/Instruction%20Manual%20-%20Water%20Boiler.pdfThis one has a BOILING/OFF button and KEEP WARM/OFF button:This one has a ON/OFF button and YOM TOV/OFF button, and 2 lights (HEATING and WARM):I am guessing that these water heater urns are identical except for the labelling. The BOILING/OFF button is equivalent to the ON/OFF button. The KEEP WARM/OFF button is equivalent to the YOM TOV/OFF button (which is a Jewish Sabbath version as per the above manual).My understanding is that the BOILING/OFF and ON/OFF buttons turn on the water heater element to the full current and it will keep going until the water in the tank is boiled, and it will keep boiling until all of the water is completely gone? It never shuts off? Do you have to monitor the tank and see or hear that it is boiling and then shut it off manually by turning the switch off again? Or is there a thermostat that will automatically pop the boiling button off again?The KEEP WARM/OFF or YOM TOV/OFF button sounds like it puts a small amount of current through the (same?) element but not enough to boil the water... Just enough to keep it heating to compensate for the heat loss of the tank.What happens when you switch on BOTH switches? Wouldn't the BOIL button over-ride the KEEP WARM if it never shuts off? Why wouldn't they use a 3-way switch... BOIL/OFF/KEEP WARM..... The Boil setting puts the full current through the element in the tank. Then after it is boiled, you flip it over to KEEP WARM and it will put a smaller current through to keep heating the water.Or I would design it with a BOIL switch that "pops" out after it has boiled the tank, like electric tea kettles which stop boiling the water. Then have a "KEEP WARM" toggle switch that lets you decide whether or not you want to keep running a smaller current through the element for keeping things warm after you've boiled the tank.I'm sure it is simple but never having owned one and looking at different models I am trying to grasp what is going on with these things, and internally how they are wired up. Thanks!

author: edy
author_rank: Super Contributor
timestamp: March 02, 2017, 03:09:51 am
content: One more thing....I noticed some Electric Catering Urns have 1 button... ON/OFF. They boil the water and when it reaches a set level (like 97 deg. Celsius) they will turn off the main element and keep a secondary element on that keeps warming the water but not enough to boil.If the water runs out, there is a safety that will turn the element off even if the button is ON. Also, you can add cold water to the urn at any time and it will turn on the primary element and boil up the water again.So I assume if the thermostat setting is say 97 degrees Celsius.... The primary boiling element is ON at any point below 97. Once it overshoots the thermostat and gets to boiling (say there is some hysteresis) it will shut off the primary element and turn on the secondary element (which is enough to keep the water warm).... Again, there is enough hystersis on the thermostat that it may need to drop down to 90 degrees to turn on the primary element again to bring it to a boil. So if you add cold water that brings it back up again to boiling, then primary boiling elements turns off and the warming element kicks in again.In that case, no matter what, as long as the thing is on... and there is still water in the tank, either the primary boiling or secondary warming element is on.So what is the deal with the 2-button versions of the urns? Is it just giving the user more control over these functions manually, and over-riding the need for the thermostat?

author: CatalinaWOW
author_rank: Super Contributor
timestamp: March 02, 2017, 03:41:12 am
content: Hopefully someone conversant with Jewish rules for Sabbath can chime in. I suspect that it relates to that. They have some very complicated rules for what can and cannot be done on Sabbath. Being able to keep something warm (but not heat from cold) is consistent with my understanding the kind of things these rules authorize.

author: edy
author_rank: Super Contributor
timestamp: March 02, 2017, 04:04:37 am
content: Thanks. I'm wondering, that first hot water urn I showed with 2 buttons marked BOIL and other KEEP WARM did not appear to be marketed towards any religiously observant customers. However, the second urn had the BOIL and YOMTOV buttons. I would guess that the 2 urns were just rebranded versions of the same thing, but without knowing the wiring/schematics or purpose I could be totally wrong in assuming how they work... and if indeed they are identical.My other guess is that in order to satisfy certain religious customs, the "automated" functions have been removed (like need for thermostat to cycle element on/off) in order for the user not to accidentally activate things. Therefore, once the water is boiled and you turn off the boiler element, you flip on the keep-warm element and it stays on at the same rate (unchanged) and never cycles, regardless of how much cold water you add.This may be enough to satisfy the religious requirements whereas a more automated one-button hot water urn will be turned on and off inadvertantly by the user as cold water is added if it is using a thermostat-based system. ?

author: RobertHolcombe
author_rank: Frequent Contributor
timestamp: March 02, 2017, 04:18:47 am
content: Its hard to tell but it appears the switches may be part of one assembly, so perhaps the boil switch will trip to the off position once the water reaches boiling temperature, and the keep warm switch is a toggle which will maintain a pre-determined temperature. Users then have "warm" water on demand and can choose to boil the water when needed. In an office or function setting this could be desirable if making a large quantity of tea/coffee, the water can be "warm" and then boiled quickly if so desired.