Wizard
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:
- a smaller 50 amp coil relay (25amp front/back) that holds the circuit whilst batteries good. ( will cost around 160mA when parked
)
- 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?
Swaggie
Trying to reinvent the wheel is always fun. Who knows, you might design a better solution.
Look for latching relays. They don't require power to hold in. Pulse to open, pulse to close.
This device came standard on my Perentie:
Products - DC Power Management - Battery run down protection - Battery Guard 2000
Have a look at the isolator Toxic Fitted to his 90.
Blue Seas make what you want.
OldBushie
Hi Manic, before you worry about a low voltage device, how are you going to power it?
Pulling even half the currents you are talking about would destroy batteries after just a few uses.
OldBushie
SupporterOriginally Posted by drivesafe
Ahh Bugger.
There goes the thermo fan idea
You only get one shot at life, Aim well
2004 D2 "S" V8 auto, with a few Mods gone
2007 79 Series Landcruiser V8 Ute, With a few Mods.
4.6m Quintrex boat
20' Jayco Expanda caravan gone
AT REST
TopicToaster
SubscriberCan you please explain you second statement?
I read it as a system which is designed for up to 100A draw, but realistically going to see much less.
And I know a system can draw way more than 100A for more than 'a few uses' without destroying batteries. Ie winch, starter motor, inverters, and stereos while the engine is off.
-Mitch
'El Burro' 2012 Defender 90.
OldBushie
Hi Toxic, and it is highly unlikely that manic will draw anywhere near 50 amps with what he is planning to use his setup for.
And something like an Optima Yellowtop could safely handle constant currents like that, but most batteries could not handle such currents for long periods of time.
Winching is usually done for just short periods of time, and starter motor currents are drawn for much shorter times.
My point is that manic most likely does not need to cater for more than about 25 amps total, not the 100 amps he is looking at setting up for, but if he was going to be drawing currents as high as just 50 amps, or more, for long periods, he could easily damage most batteries after just a few uses.
OldBushie
SupporterTry running your winch for too long without running the engine, Then see how your battery looks.
If it doesn't cook it it will most certainly be as flat as a pancake.
You only get one shot at life, Aim well
2004 D2 "S" V8 auto, with a few Mods gone
2007 79 Series Landcruiser V8 Ute, With a few Mods.
4.6m Quintrex boat
20' Jayco Expanda caravan gone
Wizard
Ha, I knew I was missing something!
The one you linked looks like it takes a 3amp pulse to switch the contact. All other times 10mA. That would work!
Seeing as I already have low voltage detection at 4mA , looks like I only need a simple latching relay. Cheers!
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