Replacing the power on relais with a battery shut off

[Roy Beukeveld]

Hi everyone,

The power module is switched on and off via a relais, the harness is shown below.
I'm planning on using a battery cutoff switch in the plus lead/wire from the battery to isolate the power completely when switched off.
Would it be a problem if I did not use the relais harness but switch the power module on directly from the cut off switch?

[Adrian Harris]

I've wired lots of tanks using that exact same switch and have had no problems, either with Armortek electrics or DIY.

Adrian.

[Roy Beukeveld]

Hi Adrian,

Good to hear you have good experiances with the same switch, i’ll leave the relais harness for what it is and wire the switch directly to the power module.

Thank you for the reply

[John Heath]

I’m fitting a battery isolation switch to my Tiger. Am upgrading most of the wiring to heavier duty silicone cable and am using 8mm bullet connectors on the battery cables.

John

[Vince Cutajar]

Hi Adrian,

Good to hear you have good experiances with the same switch, i’ll leave the relais harness for what it is and wire the switch directly to the power module.

Thank you for the reply

Good idea. This is my version:

Vince

[Mark Heaps]

I would personally wire in a battery shut off in parallel with the relay as a get you home method. Use the relay as long as it works but if it starts dropping out due to low battery voltage or fails completely, then activate the battery shut off to get the model into the car.
Mark

[Gerhard Michel]

In my 5 tanks I use an automatic circuit breaker as a main switch; from 30 to 60 amps nominal current, depending on tank model. These circuit breakers trip out at 150 % of the nominal current within about 10 seconds. This allows to consume up to 90 amps peak for this 10 seconds.

IMHO most wiring of load current circuits in the models I have seen is too poor for avoiding voltage leaks. I use 10 mm² to 16 mm² (AWG 7 to AWG 5) for the main load circuit and 100 amps bistable relays deep in the hull to control the circuits with tiny 'doll's house' switches at my control board beneath the RM hatch .

[Roy Beukeveld]

Hi everyone, thank you all for the replies, and of course a happy new year to everyone

I’m fitting a battery isolation switch to my Tiger. Am upgrading most of the wiring to heavier duty silicone cable and am using 8mm bullet connectors on the battery cables...

Hi John, do you use this switch to power up the 'power module' directly or do you still have the relais wired in?

...Good idea. This is my version: ...

Hi Vince, that's a nicely organised unit you have there, so your cut off switch is your power on switch directly as well? No relais in between?

I would personally wire in a battery shut off in parallel with the relay as a get you home method. Use the relay as long as it works but if it starts dropping out due to low battery voltage or fails completely, then activate the battery shut off to get the model into the car.
Mark

Hi Mark, Interesting application for the switch, I have been working with 24V car relais in a hobby application, and the thing that I noticed was that the relais drops out quit fast when the voltage drops. So when the relais is powered by the main battery (let's say its a lead acid), and the voltage is already lowered by normal discharge during use then a small amperage peak can cause a voltage drop high enough to drop out the relais quite easy, and leaving the tank powered off in the field. That's one reason I'm a bit holding back of using this relais harness. The other reason is that it doesn't isolate the power completely.
Your application of the switch would cover such a moment indeed, haven't thought of that.

In my 5 tanks I use an automatic circuit breaker as a main switch...

Hi Gerhard, thats an interesting component you use there. Do you have a make and part number for me so I can look into it?

[Vince Cutajar]

Hi Vince, that's a nicely organised unit you have there, so your cut off switch is your power on switch directly as well? No relais in between?

Hi Roy
I kept all the original Armortek wiring. That big red switch is acting as an isolator cutting the positive line when it is in the OFF position. Without the isolator the batteries will continue to very slowly discharge.

Vince

[Adrian Harris]

> Without the isolator the batteries will continue to very slowly discharge.

That is only true of the older black and silver modules.

The new red modules are completely isolated by the relay, so no current drain when off.

Adrian.

[Gerhard Michel]

Hi Roy,

I bought these components years ago from a military surplus dealer; mine come from cannibalized tanks (full scale).

But also other dealers (e.g. EBAY) offer such components in new state. Here 2 pics of a switching fuse and a bistable relay. The dual fuse has only 2 x 7 amps nominal current and is only suitable for control circuits, but the shape is similar.



The bistable relays ar very useful components, because they can swith very high load currents with low control current, and they consume this low current only in the switching moment, not when active! A normal relay consumes power all the time it is active, a bistable relay works only with pulses, one for ON and another for OFF. Therefore two simple pushbuttons are sufficient to manage a bistable relay. I recommend a LED to show the switching state of the relay.

[Roy Beukeveld]

...The new red modules are completely isolated by the relay, so no current drain when off...

Hi Adrian, that's useful to know, thank you

...mine come from cannibalized tanks (full scale)...

That gives a nice touch to it

...because they can swith very high load currents with low control current, and they consume this low current only in the switching moment, not when active!

Very interesting indeed, the relays I worked with were all mono stable so there was always a small current flowing. The bistable relay as you explain it would then also be non sensitive to drops in the voltage used to keep the relay switched in the desired position (eliminating the risk of the relay unwanted dropping off).
Thanks for mentioning

[Mark Heaps]

The bi-stable relay will stop unwanted "drop-outs". It will also stop you getting a warning that you need to get that model into your vehicle ASAP.
Getting a SdKfz 7 across 30 meters and into the car was not fun.
Mark

[Gerhard Michel]

Well, also a warning given by a normal relay may be too late even when using simple lead acid batteries. When using LiFe cells this would be absolutely no practicable possibility. A BMS however would cause a final stop of the tank. IMHO a reliable monitoring of the battery state is the best solution giving a 'just in time" warning AND yet the option to move the tank to its target. The time the tank can be used after receiving the warning can be adjusted individual by setting the warning voltage level.

[Roy Beukeveld]

Interesting to hear the different experiences with this.

Parallel wiring of the switch across the relais to get it home after the drop out of the relais (is interpreted as a warning) is basically using something in your advantage while I saw it as a threat.

That in case of LiFe it wouldn't work makes sense too. I will be monitoring the voltage and use lead acid batteries.
Is there a reference value for low voltage to look out for? Experience value from which you know is a good one to use as a threshold voltage to get a StuG back to the car?