Snackspace Heaters

Snackspace Heaters
Primary Contact	Asj
Created	01/12/2024
Completed	{{{completeddate}}}
Dormant	{{{dormantdate}}}
Version	{{{version}}}
Members	{{{members}}}
Manufacturer	{{{manufacturer}}}
Model	{{{model}}}
Location	[[]]
GitHub / Repo	{{{repo}}}
Status
Type	Hackspace Infrastructure
Live Status	{{{livestatus}}}
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The "tap for heating" nh-tools box

Using nh-tools, we are beginning to install heaters around the hackspace, where the usage costs can be covered by snackspace. We currently pay 50.4p/kWh of electricity, which means a 2kWh heater for an hour costs over £1.

Why do we want / need this?

That's a good question.

• We've seen space heaters being sat on fabric chairs multiple times. This would be an embarrassing way to start a fire. Keeping the heaters wall mounted is far safer.
• Some very lovely members try and cover their heating use with a donation, many do not and we simply can't afford it.
• IR heating is more efficient in large open spaces like the hackspace. Instead of heating the air, we are heating you!

The space is happy to cover the cost of heating for paid workshops and large get meetings / get-togethers.

Construction

Differences to normal nh-tools

There are a few tweaks which should be made to the standard nh-tools to make it more appropriate for heating.

• Removal of the induct LED and button. This can reduce the chance of confusion as people might think you need an induction for using the heaters.
• Changes to the nh-tools code to allow a "tap once for 30 minutes" style of use, rather than leaving your card in. Inserting the card increases the chance of the user walking off, forgetting their card, and having the heating left on unattended.

The following git diff can be applied to nh-tools code to allow the heating to stay on for half an hour after tapping a card.

diff --git a/nh-tool/Config.h b/nh-tool/Config.h
index ea8b318..421b49c 100644
--- a/nh-tool/Config.h
+++ b/nh-tool/Config.h
@@ -74,7 +74,7 @@
 // buffer size
 #define DMSG  50
 
-#define TIMEOUT_SES  (1000*15) // 15s - Session timout - how long to wait without seeing the card before disabling tool
+#define TIMEOUT_SES (unsigned long)1800000
 
 #define INDUCT_TIMEOUT 30     // How long in seconds to wait for card when in the induct state
 #define INDUCT_FLASH_FREQ 250 // how fast the induct led flashed after induct button pushed (lower is faster)

Assembly

If using the front PCBs (which reduce the amount of hand wiring required), omit the induct LED and switch. The modified nh-tools heater box front does not have holes for these.

Heater Modifications

The heater used is a Devola Core 2kW heater. This has digital controls on the front which switch in and out two relays to have three temperature levels. The modification is quite simple and requires the removal of the two transistors which switch these relays. The emitter and collectors of these two transistors can be connected together, which can then pass through the nh-tools relay. This ensures only low voltage and low current switching is performed by nh-tools.

• 
  Component side, showing the two transistors which should be removed.
• 
  Trace side, showing how the emitter and collector pads from the where the transistors were have been tied together with wires running off to nh-tools.