redarc vs12 voltage sensor

Submitted: Sunday, Dec 06, 2015 at 11:05
ThreadID: 131055 Views:2629 Replies:3 FollowUps:7
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Gooday there : i'v got a redarc VS12 voltage cutout sensor and was wondering is there any easy way of checking what voltage it drop out when adjusting from its std setting .
wired for low voltage cut out
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Cheers Nick b
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Reply By: Zippo - Sunday, Dec 06, 2015 at 13:10

Sunday, Dec 06, 2015 at 13:10
The problem is that you need to be able to control the INPUT VOLTAGE to create the required trigger voltage. Obviously you could just sit there with all the appliances - headlights, vent fan, ... - turned on (engine off) and wait for the voltage to droop to your desired set-point, but that's going to take a lot of your day and get old really quickly.

Plan B is to source an adjustable DC power supply and connect that to the relay input. It would need to be a low ripple supply. Then simply set the power supply output to your required set-point (using an accurate digital multimeter) and adjust the VS12 pot as per the instruction sheet (clockwise increases) to get the required result.

I know that not everybody has such a PSU at hand, but that's the only real way to set it properly that I can see.
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Follow Up By: Member - nick b - Sunday, Dec 06, 2015 at 15:07

Sunday, Dec 06, 2015 at 15:07
Okay thanks for your reply , I have done plan A & as you say takes some time & not that easy !!
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Follow Up By: Kazza055 - Sunday, Dec 06, 2015 at 16:06

Sunday, Dec 06, 2015 at 16:06
I have one of these DC-DC units (http://www.ebay.com.au/itm/DC-DC-3-35V-12V-to-3-5-35V-100W-Boost-Step-up-Power-Supply-LED-Voltmeter-Module-/271812026248?hash=item3f49425f88:g:o9gAAOSwv0tVC8UY) that I purchased to do just what you want to do.

Connect it to you battery and then you can adjust the output voltage to what you require.

Handy little devices, I use a couple of them to run my network gear when away in the van, they eliminate any excess voltage that you might get while the van batteries are being charged. Also if using individual units they will isolate each of the output voltages.
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Follow Up By: Zippo - Sunday, Dec 06, 2015 at 18:46

Sunday, Dec 06, 2015 at 18:46
Kazza, if they are as specified (and with Chinese stuff you can never really be sure) then I'd have two concerns. The ripple is a bit high, and so the trip threshold will be affected somewhat. But more importantly, it states STEP-UP. For setting a low voltage cutout you really need to lose a bit of voltage, not gain some. Of course, if you have a suitable means to reduce the input below normal battery volts that would not be an issue.
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Follow Up By: Kazza055 - Sunday, Dec 06, 2015 at 19:04

Sunday, Dec 06, 2015 at 19:04
From part of the specs it claims

Input Voltage: 3-35V DC
Input Current: 9A (Max)
Output Voltage: 3.5-35V DC

This one will definitely go lower than 12 v and being buck boost the output can go higher than the input.

As I mentioned I am running network gear on some, this gear includes a NAS drive, Dovado Pro router with Sierra 320U modem and there is no problems with ripple that I have noticed.
My reason for using these was to ensure that the DC supply to these devices was a constant voltage.

Regards to this post, they provide a cheap and simple method of reducing the 12V supply to test the low voltage cutoff - the display will read the output voltage.
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Follow Up By: Zippo - Sunday, Dec 06, 2015 at 19:42

Sunday, Dec 06, 2015 at 19:42
Kazza, I read the specs on that feebay listing (and those on others listing the identical item). Nowhere does it say buck-boost - which isn't to say that it isn't, but the kindest I can be is believe what they say.

40mV ripple isn't going to worry most load equipment, but when you are trying to set a cutoff threshold the dips are what will trip the device, not the average which is what their voltmeter (or yours) will be displaying. Maybe not a big deal, but a matter of principle if you want it set right.

I have several home-made devices that function like the VS12 which I use to control battery charging. Despite setting the thresholds accurately on a decent DC PSU, the ripple in *most* basic battery chargers causes operation at significantly different on/off voltages. YMMV.
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Follow Up By: Member - nick b - Tuesday, Dec 08, 2015 at 09:17

Tuesday, Dec 08, 2015 at 09:17
thanks again :-) But you blokes are talking a different language ...hahaha
I'm more of a hammer & chisel man

So in summing up what my best option here inc Allan B switch ?
& how will i go about it .

thanks
Cheers Nick b
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Reply By: Allan B (Member, SunCoast) - Monday, Dec 07, 2015 at 11:04

Monday, Dec 07, 2015 at 11:04
Yes Nick, there is a very easy and economical way to do this.

Obtain a 1k potentiometer (Jaycar RP-7504 $2.50 or similar) and connect it as shown in the photo below. The output voltage to the sensor can be varied between 0 and 12 volts by simply rotating the knob-shaft of the potentiometer. Do not have any load connected to the sensor during the test.
Connect your multimeter to the leads to the sensor to monitor the applied voltage.
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Reply By: Member - nick b - Tuesday, Dec 08, 2015 at 09:43

Tuesday, Dec 08, 2015 at 09:43
Does anyone have suggestion on what voltage i might set this to ?
I want to save battery the from damage from over dis charge .
deep cycle wet cell 100ah battery running few light & 40 lit fridge
leaving lights/fridge on etc just in case not situation .
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Follow Up By: Allan B (Member, SunCoast) - Tuesday, Dec 08, 2015 at 10:00

Tuesday, Dec 08, 2015 at 10:00
12.2 volts is considered 50% SOC for this battery type. However this figure is for a battery sitting with no charge or discharge taking place. However, as the VS-12 will be protecting the battery whilst discharge is taking place and the terminal voltage will be slightly depressed, I would set it to trip at 12.0 volts which should protect the battery from being discharge below 50% and therefore optimise its life.

p.s. Member Message sent to you.
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