Thread: An efficient 100Amp low voltage cut out?

Originally Posted by Mick_Marsh

50 amp cable is cable capable of carrying 50 Amperes of electrical current without destroying itself or catching fire. I'd have thought you'd know that.

Sorry Mick but cable is not sold based on current capacity because the intended end use governs the size of the cable.

For example, 6B&S ( 13.5mm2 ) cable is rated at over 400 amps when used as starter motor cable but only 105 amps when used as Dual Battery cable.

Years ago 6mm AUTO cable used to be marked as “50 amp” cable, but this only applied when the cable was used in a 50% cycle application. When used in a 100% cycle application, it has a maximum safe current rate of around 35 amps. So this practice no longer exists.

I was not sure of what manic was intending to use as “50 amp” cable, hence my statement.

Again there is no such thing as 50 amps cable.

Originally Posted by drivesafe

Again there is no such thing as 50 amps cable.

You repeated your statement, I'll repeat mine.

Originally Posted by Mick_Marsh

Again, 50 amp cable is cable capable of carrying 50 Amperes of electrical current without destroying itself or catching fire.

Have a read of the OP? Do you have an understanding of what he is trying to achieve, and here's a hint, it's not about pulling a constant 100A out of a battery, no matter what colour top it has?

I understand what you are saying but I can't see how it ties in with the original enquiry. All it serves is to muddy the waters.

Originally Posted by Mick_Marsh

You repeated your statement, I'll repeat mine.



Have a read of the OP? Do you have an understanding of what he is trying to achieve, and here's a hint, it's not about pulling a constant 100A out of a battery, no matter what colour top it has?

I understand what you are saying but I can't see how it ties in with the original enquiry. All it serves is to muddy the waters.

Correct, it's not about pulling 100 amps, it's about pulling as much as 50 amps total. Read manic's first post.

Originally Posted by drivesafe

Correct, it's not about pulling 100 amps, it's about pulling as much as 50 amps total. Read manic's first post.

I don't see where he says he will be pulling 50A either. I do see where he is pulling 4mA.

Originally Posted by manic

I need to solve some issues with my DIY low voltage cut out.

The set up is simply:

• A voltage detector circuit that provides a 12v trigger when batteries are good, cuts power when batteries running too low. (Consumes only 4mA max)
• 1 x 100Amp relay (energised by the above board)

This gives me a 50amp line to front of vehicle (stereo, uhf, power ports etc) and 50 amp to the back (exterior lights, fridge, anderson plugs etc). That's an overkill but it gives me power in reserve.

Problem is the 100Amp relay uses enough power holding the relay closed to significantly drain the battery if car is left standing for over a week.

I could use a normally closed relay and trigger the relay to disconnect the circuit when voltage is low, but then I would be using power out of my low batteries to hold that disconnected state. So I have to rule that out.

I looked at solid state relays. At 100amps they need a big heatsync (not really a problem), but all that heat translates to losses. I'm not sure how much would actually be lost through an SS relay but I'm worried the losses will significantly reduce the amount of aux battery time I get when camping.

Ideally I would like to keep under 25mA parasitic drain when the car is parked with everything switched off. I have been isoltaing the batteries recently, but constantly having the stereo boot up in demo mode is starting to drive me nuts.

I've kind of resigned myself to downgrading the capacity on the circuit, and perhaps do one of the following:

1. a smaller 50 amp coil relay (25amp front/back) that holds the circuit whilst batteries good. ( will cost around 160mA when parked )
2. or a 50 amp solid state relay that provides a lossy power supply?

Any one on here have a brighter idea, or informed opinion on which of these options is better?

As I said in a previous post, I have one of these devices. It comes in either 100A or 200A. It does not come in 35A, 6B&S or 13.5mm2. There has got to be a reason for that.

Originally Posted by drivesafe

This statement is about as low as a person can get. I have made no reference to my gear and have done nothing more than postnup info to help the OP with what he was trying to do.

That claim is nothing more than you trying to draw attention away from the endless B/S you have been posting up and getting caught out on.

Ha. Cute.
Most people around here already know that I'm a ****. Welcome to the club, buster.

Ah, tapatalk crash, well crafted reply lost....

I've been on this forum long enough to know drivesafe will rarely ever miss out on a battery/charging related thread. So I was hoping he would contribute here too.

My init post might have been better if I simply asked ' how best to hold a 100amp circuit open/closed with the least amount of parasitic drain'.

I appreciate all contributions where attempts are made to help. I beleive drivesafe was just trying to understand the broader application in order to tailor some advice.

So anway, a latching relay is what I need. But not as straight forward as I initially hoped. I will need a second circuit, probably centered around a PIC controller or 555 timer in order to pulse the relay open/closed.

Im getting lazy and looking at a latching relay from sterling-power. Programable cut in/out and an idle consumption of just 0.5mA!

Latching Relay Pro Latch R | Sterling Power Products

interVOLT PSR12150 - 12V 150A Solid State Programmable Voltage Sensing Relay | Battery Business

10mA unswitched with display off.

Originally Posted by Milton477

interVOLT PSR12150 - 12V 150A Solid State Programmable Voltage Sensing Relay | Battery Business

10mA unswitched with display off.

I did see this one. 10mA idle is good enough but being a solid state relay whats the current/voltage loss under load?