G'day, think my matson dual battery isolator is not working properly. Has just had a new cranking battery installed and a new deep cycle. I'm not sure how these battery systems work (forgive my ignorance) on the isolator it say cut in 14.4v and cutout 13.3v. What does this mean? My second battery won't charge after it has had my fridge on it, voltage drops below 9 volts. I would think the isolator should kick in at that low voltage really? It's barely running my fridge at that voltage. The solenoid does not have a manual override switch either. Any way I can check what is or isn't working. Thanks for any input. Matt
Matson dual battery isolator.
- Thread starter atcmatt
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Ben_W
Member
Hi Matt,
The purpose of the isolator is to separate the cranking battery from the auxiliary (and any load connected to it) to prevent the main battery from discharging to the point that it is unable to start your vehicle. When the switch in the isolator is closed, the two batteries are connected in parallel so essentially you have one circuit and the voltages of both batteries equalise each other and remain roughly the same. As soon as the isolator (or voltage sensetive relay) senses that the voltage drops below 13.3V it cuts out (the switch opens) separating the two batteries. The voltage in the main battery should then not drop any further, allowing it to still start the vehicle. The auxiliary battery will continue to discharge as long as there is a load (fridge etc.) connected to it until it is dead flat. Once you start the vehicle, initiating charging from the alternator or apply some other charging source to the main battery, the voltage in that battery will increase until it reaches 14.4V. At that point the isolator cuts in (the switch closes) allowing charge to flow to the auxiliary battery. Hope that makes sense.
I'm not sure what yours is doing but when you say your auxiliary is getting down to 9V and not charging, is that with the engine running? And is the voltage in the main battery getting above 14.4 volts? If you don't have battery monitors can you check it using a multimeter?
Cheers,
Ben
The purpose of the isolator is to separate the cranking battery from the auxiliary (and any load connected to it) to prevent the main battery from discharging to the point that it is unable to start your vehicle. When the switch in the isolator is closed, the two batteries are connected in parallel so essentially you have one circuit and the voltages of both batteries equalise each other and remain roughly the same. As soon as the isolator (or voltage sensetive relay) senses that the voltage drops below 13.3V it cuts out (the switch opens) separating the two batteries. The voltage in the main battery should then not drop any further, allowing it to still start the vehicle. The auxiliary battery will continue to discharge as long as there is a load (fridge etc.) connected to it until it is dead flat. Once you start the vehicle, initiating charging from the alternator or apply some other charging source to the main battery, the voltage in that battery will increase until it reaches 14.4V. At that point the isolator cuts in (the switch closes) allowing charge to flow to the auxiliary battery. Hope that makes sense.
I'm not sure what yours is doing but when you say your auxiliary is getting down to 9V and not charging, is that with the engine running? And is the voltage in the main battery getting above 14.4 volts? If you don't have battery monitors can you check it using a multimeter?
Cheers,
Ben
those cut in and cut out voltages indicate its setup to only link them while the engine is running and separate them when the engine is off
The issue you're probably having is that your alternator may never get up as high as 14.4v so they are never linking and therefor your second battery is not getting charged
The issue you're probably having is that your alternator may never get up as high as 14.4v so they are never linking and therefor your second battery is not getting charged
Thanks Ben and Jerone. Yeah that explains it well Ben. Well my cranking battery has never gone flat on me. So I'm guessing something is working right. My aux battery now is on 6 volts. While the main battery still has plenty of juice (able to start the car easily, will check voltage when I get home with multi meter) so when the car is running the alternator should be charging the battery at 14.4 or more to be able to close the circuit to charge the auxiliary battery then? I will have to check that also when I get home. I guess I could put a 240v charger on the main battery and see what happens then to see if the solenoid closes. Maybe like you said Jerone the alternator is not getting upto or past that 14.4 so the solenoid is not working. What can I do to rectify that if that is the case? New alternator, regulator or a different solenoid that kicks in at a lower voltage? Thanks very much fellas for your help.
Sorry guys, made a mistake. It's actually cut in at 13.3 cut out 12.8. I have checked my battery voltages. Main battery with motor not running is 13.3 with motor running (charging) it's at 14.4. Checked the positive just before the isolator and it is also at 13.3 and 14.4 respectively. With the car off the auxiliary batter is at 9.1 with it running it is at 9.1. Checked the positive wire on the other side of the isolator (going out to the aux battery) and it reads the same as the aux battery at the terminals. Both with car on and off it is at 9.1v. I then put on my mains charger on the main battery and it was reading 15v. I'm just down to the conclusion that the isolator is shagged. What are your thoughts?
Matt
Matt
Ben_W
Member
Yep, sounds like it. Either the solenoid is buggered & not cutting in, or the switch is faulty (contacts dirty, burnt out). Do you hear it trying to cut in? With my Redarc isolator I hear a loud click when it cuts in, it's audible in the cab with engine running.
It used to work when i had the old aux battery on it, has not had a battery in it for a while. I reckon it's worn out. I used to hear it click all the time, because the old battery was stuffed, it used to not hold charge so it was always cutting in and out, maybe the reason the isolator is now stuffed? Thanks blokes.
bods
Member
Nah, they're designed to cut in whenever the main battery gets above those volts. Overnight the surface charge will dissapate and the isolator will disconnect the batteries even with no load on either of them.
I have a projecta on mine and can hear the click shortly after starting the motor in the morning. During the day, short stop / start driving the voltage doesn't drop enough to cut out, although it will when cranking as the main battery will go below 12.8...
Essentially they are a hard core relay, so will always wear out...
No worries cheers, well I have just ordered a new one. Have been doing a bit of research also and it seems like those dc to dc chargers would be the best system for the dual batteries, less work for your alternator anyway. At 250 plus I'll stick with the isolator for now. Cheers.
bods
Member
Yeah same hey... in saying that if I end up getting an agm for a replacement aux battery I will dish out for a dc - dc charger....
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Got a new matson one through the post, fried the thing already, stupid me left the positive in the bottom of toolbox not connected and earthed out and short circuited! Not happy!!! Anyway, just bought a dc to DC charger. Should have done it in the first place!!! Cheers.
