observations about redarc isolator
Submitted: Wednesday, Mar 25, 2009 at 00:06
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greybeard
Decided to change out my battery isolator with a redarc smartstart.
Have been observing it's operation over the last few days and have been pondering aspects of that operation.
I'd point out that it is operating as per the specification, apart from the current drain of the actuated solenoid being around the 0.8A mark instead of 13.5V for at least ~ 4 seconds. all good :)
When the engine is switched off it stays actuated until the voltage drops to < 12.5V. Now herein lies the conundum. My main battery is an N70ZZ and my secondary is a 55Ah AGM ( and the camper is a 95Ah deep cycle ). With no load, apart from the actuated solenoid on the smart start, the combined battery voltage takes over 12 hours to drop to < 12.5V
In that time the smart start has used up ~ 10Ah of battery capacity.
Granted it means my fridge ( when connected ) can draw down some power from the starting battery but it also means i'm wasting battery capacity.
And ( i know you need to let the batteries rest for 12 hours but it is a pretty low discharge rate compared to the combined battery capacity ) 12.5V is about 75% charged.
The discharge times and battery capacities don't quite add up but roughly speaking i'm using up nearly half a day of fridge running power just because the smart start won't drop out until the battery volts drops below 12.5V.
I can force it to drop out by leaving the headlights on high beam for a minute or so after i turn off the engine but it all seems counter productive.
I'll have a chat to redarc about it but can anyone, apart from mainey, see anything i'm missing in all of this?
Reply By: greybeard - Wednesday, Mar 25, 2009 at 09:25
Wednesday, Mar 25, 2009 at 09:25
thanks guys.
it's a catch 22. if the solenoid ( and it can be any solenoid ) didn't draw so much power it wouldn't be an issue.
if the switch off voltage was, say, 12.8V then it wouldn't be an issue.
as it is, all that is gained by leaving the drop out voltage at 12.5V is for all of the batteries to power the solenoid for a 'half a fridge day' ;)
The only other reason I can see for the 12.5V drop out is to provide some hysteresis to cope with noisey vehicle electrics. There is a time delay in the controller that should do this anyway.
But, I'm not an expert on electrical noise in vehicles :)
One other possible point ( for the electrical/electronic people out there ) is I know with a relay it requires more current to activate the relay than it does to hold it in the activated state. ie reducing the power consumed by the relay once activated. Is it the same principle for a solenoid? If it is then this may be an option to reduce the power consumption of the solenoid.
I'll wait to hear what Redarc have to say.
AnswerID:
356043
Reply By: Member - Matt M (ACT) - Thursday, Mar 26, 2009 at 13:10
Thursday, Mar 26, 2009 at 13:10
Greybeard,
I'm NOT proposing this as a solution to your problem, just an interesting observation.
I also have a
Redarc isolator fitted, although I think mine has 12.7V cut out (must be an older model). I also have a voltage booster fitted. What I notice is that the booster continues to draw power from the cranking battery after the car has shut down and charge the auxiliary battery. Once the cranking battery gets to 12.7V, the
Redarc disconnects and charging stops. This usually happens pretty quickly (dependant on the aux battery SoC), but I guess that instead of the cranking battery 'surplus' powering the
Redarc for a period of time, it 'scavenges' power from the cranking battery and stores it in the aux battery.
Again, not a viable answer for you, just an observation.
Matt.
AnswerID:
356320
Follow Up By: greybeard - Thursday, Mar 26, 2009 at 13:28
Thursday, Mar 26, 2009 at 13:28
there was a change in the operating points on the
Redarc a few years ago to cope with some of the newer vehicles. sounds like you've got an older model.
for my application i'd like to see a similar drop out voltage. I know they can be programmed so i'll give
redarc a call.
cheers
FollowupID:
624314
Reply By: Maîneÿ [wa] - Friday, Mar 27, 2009 at 15:41
Friday, Mar 27, 2009 at 15:41
As I was named in the original post: "I'll have a chat to
redarc about it but can anyone, apart from mainey, see anything i'm missing in all of this"
I think it's time now to put my 'opinion' forward.
I've previously used a 'mechanical solenoid' and noticed it did have a similar Voltage drop as stated by GB, I replaced the 'mechanical solenoid' with an 'electronic charge
isolator' using a Rotronics MH10 because it has a Voltage Drop of just 0.05 Volts.
Obviously the lower the voltage drop the more efficient the charge
isolator is.
Solenoids can drop up to 0.6 Volts.
This voltage drop reduces the amount of charge the auxiliary battery will be able to receive, causing the auxiliary battery to charge to only ~70% in many cases.
Mainey . . .
AnswerID:
356595