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Topic: Looking for a 15A relay (Read 1 time) previous topic - next topic

DanCro0312

Oct 24, 2018, 11:58 pm Last Edit: Oct 24, 2018, 11:59 pm by DanCro0312
Hi all,

I've seen a lot of relays rated for 10A, but I'm looking for a 15A relay (1 Channel).  The system is a 24V system if thats a factor.  I'm located in the USA and I would prefer a US vendor to minimize shipping time.  Any help is greatly appreciated!

- Dan

WattsThat

This relay will be switching what kind of load? Voltage?
Vacuum tube guy in a solid state world

DanCro0312

#2
Oct 25, 2018, 06:52 pm Last Edit: Oct 26, 2018, 04:03 pm by DanCro0312
Basically there will be a 22.2V 15A battery bank *with a BMS 6S4P 3.7V 3.2A Li-ion* powering a 24V heater (yes, heater won't be 100% effective) controlled by a relay switch.  The relay switch will be connected to a 5V Arduino Mega.  Hope I answered your question and thanks for the reply!

* = edit

WattsThat

Is the heater really rated at 333 watts (22.2*15)?  Just because the battery is rated at 15A doesn't mean you need a relay for that much current. You size the relay to the load and the load type.

A properly selected mosfet would work but let's first get to the actual specifications. What is the actual heater rated wattage and voltage?
Vacuum tube guy in a solid state world

DanCro0312

Here is the link for the heater: http://catalog.minco.com/catalog3/d/minco/?c=products&cid=3_6-all-polyimide-thermofoil-heaters&id=HAP6947

Going off of what you were saying, would you recommend maybe lowering the amperage prior to the relay?

jremington

#5
Oct 25, 2018, 08:32 pm Last Edit: Oct 25, 2018, 08:37 pm by jremington
The linked thin film heater won't draw much current, about 0.6 A from a 22V power supply. Oddly, the manufacturer rates its capacity as "0.0 Watt".

What will you be heating with it?




DanCro0312

#6
Oct 25, 2018, 09:46 pm Last Edit: Jan 09, 2019, 05:52 pm by DanCro0312
I have attached some documents that may better explain the system.  The "0 Watt" bothered me too but the thermal engineer insisted on that heater. 

The main goal is to keep an insulated box between 0℃ and 40℃, the Arduino mega will be program to turn the heater on around 5℃ and off around 20℃.  The relay is used because the Arduino max output is 5V which is too low for the heater. 

Attached to the Arduino is Temp Sensor, Current sensor (iC), and Voltage sensor (VS).  The iC and VS will monitor battery and be a able to output that data [A whole other problem]. 


-Dan

Edit: Removed Schematics

jremington

#7
Oct 25, 2018, 09:57 pm Last Edit: Oct 25, 2018, 10:00 pm by jremington
It would be much better to use a logic level MOSFET (for example, this one) instead of a relay, as shown below. That way you can precisely control the power output of the heater using an Arduino PWM output. The diagram is for a motor, but for a heater, you don't need the parallel diode and capacitor.


MorganS

Or a dedicated 24V driver chip like a BTT6010. That takes care of all the complexity of driving a high-power mosfet and gives you feedback so you can measure how the heater is doing.
"The problem is in the code you didn't post."

jremington

#9
Oct 26, 2018, 04:00 am Last Edit: Oct 26, 2018, 04:01 am by jremington
This is not a "high power" application or MOSFET. The heater draws 600 mA at 22 V (13 W max) and the circuit shown will easily handle it.

MarkT

You neglected to provide a link to the battery, which I can tell you now is not a 15A battery - there's
no such animal.

15Ah is entirely plausible, that's the capacity rating, not a current rating.

The load is 38 ohms, so as indicated above you have about 0.6A to switch, even a 2N2222 BJT can
just about do that (with a 150 ohm base resistor).

A logic level MOSFET or a darlington are better options (less close to the package heat limit,
especially with a heatsink).

What you will need also is a 1A fuse to protect the wiring and battery in event of a short circuit -
this goes inline with the battery +ve terminal usually, close to the battery.  Your 6S LiPo pack
(guessing from the 22.2V rating) is capable of perhaps 100's of amps on a short, this is a fire
hazard and you must protect against this in unattended equipment.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

MarkT

Basically there will be a 22.2V 15A battery bank powering a 24V heater (yes, heater won't be 100% effective)
Freshly charged you'll have 25V, discharging down to perhaps 20V, so the heat output will vary
significantly with SoC of the battery, note.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

DanCro0312

You neglected to provide a link to the battery, which I can tell you now is not a 15A battery - there's
no such animal.
My apologies, the BMS is a 6S4P 3.7V 3.2A battery system (will add an edit to previous post).  I have attached the battery specs as requested. 

- Dan

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