Hi there. I had a CTEK installed for around 12 months now. I have my service battery in the rear of my ute in a toolbox, about 2m away from the alternator and starting battery. I Have run a + cable from my starter battery to my Ctek. Then I have earthed the negative on the CTEK to my chassis. I am running a 100ah and an 85ah lead acid deep cycle batteries. I am having decent results when I just have the 100ah battery on (85ah battery is able to be disconnected) however when I have both batteries together it seems to take a very long time to charge my two batteries and they never seem to get a full charge. Is it going to be beneficial for me to run a thick earth wire from my main battery to my CTEK earth terminal. Or is having it earthed to the chassis fine. Thanks for any help. Matt
CTEK Questions.
- Thread starter atcmatt
- Start date
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You generally should never parallel two batteries of different capacities. The charger will begin charging them just fine, but the smaller capacity battery will finish bulk stage sooner (the voltage will peak) and the charger will enter absorption stage. Both batteries will continue charging but at a much slower rate until the charger enters float mode which will be sooner than it should because of the smaller battery.
Mismatched batteries also "self discharge". Once off the charger, the smaller battery will try to top up the larger one, then they'll switch places until they are both discharged.
Two improvements to make: first, bring a heavy earth cable into the tub from the front. Experience has shown that chassis earth is not always reliable (and it'll fail when you need it most). Second, either use a DC-DC charger between the two batteries or invest in a pair of more closely matched batteries.
I should also point out that a 100Ah AGM battery manufactured in Jan 2015 does NOT have the same capacity as a 100Ah AGM battery manufactured in Jan 2016. It's better than mismatching the capacity but even that small a different will lead to self-discharge and poorer charging than could be achieved.
Mismatched batteries also "self discharge". Once off the charger, the smaller battery will try to top up the larger one, then they'll switch places until they are both discharged.
Two improvements to make: first, bring a heavy earth cable into the tub from the front. Experience has shown that chassis earth is not always reliable (and it'll fail when you need it most). Second, either use a DC-DC charger between the two batteries or invest in a pair of more closely matched batteries.
I should also point out that a 100Ah AGM battery manufactured in Jan 2015 does NOT have the same capacity as a 100Ah AGM battery manufactured in Jan 2016. It's better than mismatching the capacity but even that small a different will lead to self-discharge and poorer charging than could be achieved.
Thanks for the reply Tony. Seems to make sense. I will try running a big cable from front to my battery in the tray. See if it makes a difference. Basically my wiring job is as follows.... have used all the recommended cabling as per the CTEK manual.
Main battery/Alternator to alternator in on CTEK.
Battery +IVE out on CTEK to positive auxiliary battery
-IVE on CTEK to negative auxillary battery.
Cable from auxillary battery negative to chassis earth.
To me that all seems right. Maybe all it will take is running a full cable from the starter battery to the negative on the auxiliary battery as opposed to chassis earthing it.
As of right now I'm getting
13.5 volt at my Aux batteries from CTEK with motor running putting out 14.4volts at main battery.
Seems low to me as the two auxiliary batteries were pulled out today and have been charging on 240v all day and were at 14.4 when I turned the charger off.
Thanks again.
Matt
Main battery/Alternator to alternator in on CTEK.
Battery +IVE out on CTEK to positive auxiliary battery
-IVE on CTEK to negative auxillary battery.
Cable from auxillary battery negative to chassis earth.
To me that all seems right. Maybe all it will take is running a full cable from the starter battery to the negative on the auxiliary battery as opposed to chassis earthing it.
As of right now I'm getting
13.5 volt at my Aux batteries from CTEK with motor running putting out 14.4volts at main battery.
Seems low to me as the two auxiliary batteries were pulled out today and have been charging on 240v all day and were at 14.4 when I turned the charger off.
Thanks again.
Matt
happy john
Member
The Ctek will back the charge off if in hot weather Matt. Thats what the sensor on the long cable is for. Mine will sit on 13.1 for a while on a 35deg day then belt 14.5 volts in first thing in the morning when it's cooler. The earth needs attention too, that will never be as reliable or effective as a nice thick cable.
Hi John, thanks for the reply also. That does make sense also. The battery is inside a box inside of my black canvas canopy on a steel tray so I would assume it gets pretty hot in the sun.
Have also been doing a bit of research on the different AH batteries run in parallel. Some people say is ok, some not. I believe what old Tony has told me as it's probably all first hand experience, I might add that the batteries were bought at the same time, from the same place and are the same brand and everything. Still not ideal I guess. Think I'll just stick with the 100ah as my main Auxiliary battery, will keep the 85ah battery on a trickle charger on the 240v at home and when it's needed on a big trip it can just be a backup standalone in the back of the ute to pickup a couple extra days running the fridge.
Too broke right now to be buying two new batteries to run in parallel. Big trips these days are all pipe dreams anyway with our busy lives. Only really get weekenders and the 100ah will be plenty to run the cfx50 and a couple strip LEDs for a weekend.
Anyway I'm definitely going to get some 10mm cable and run a solid earth wire back to the Auxiliary battery. Thanks again for your help fellas.
Matt
Have also been doing a bit of research on the different AH batteries run in parallel. Some people say is ok, some not. I believe what old Tony has told me as it's probably all first hand experience, I might add that the batteries were bought at the same time, from the same place and are the same brand and everything. Still not ideal I guess. Think I'll just stick with the 100ah as my main Auxiliary battery, will keep the 85ah battery on a trickle charger on the 240v at home and when it's needed on a big trip it can just be a backup standalone in the back of the ute to pickup a couple extra days running the fridge.
Too broke right now to be buying two new batteries to run in parallel. Big trips these days are all pipe dreams anyway with our busy lives. Only really get weekenders and the 100ah will be plenty to run the cfx50 and a couple strip LEDs for a weekend.
Anyway I'm definitely going to get some 10mm cable and run a solid earth wire back to the Auxiliary battery. Thanks again for your help fellas.
Matt
happy john
Member
Correct Matt the CTEK will maintain the aux in the same manner. Obviously unless you have a 20 amp 240 volt charger the CTEK will charge at the rated capacity of the charger and bring the aux up to the correct voltage over a longer duration.
The obvious problem with charging the batteries this way is that the C-Tek is going to be confused by the disparity in voltages. A long cable will necessarily have some voltage drop so the aux battery will appear to have a lower voltage. That's aside from the fact that you generally should avoid charging (at the same time) batteries of different types and capacities.
While you could charge in the way you seek to, you may not (probably won't) get a full charge at least in the aux battery. The best thing to do is charge the aux independently. Connecting the charger to the aux battery while the ignition is off is safe if you hav an isolator - the isolator won't connect until the starter battery voltage rises above its preset level (usually around 13.2V-13.5V).
While you could charge in the way you seek to, you may not (probably won't) get a full charge at least in the aux battery. The best thing to do is charge the aux independently. Connecting the charger to the aux battery while the ignition is off is safe if you hav an isolator - the isolator won't connect until the starter battery voltage rises above its preset level (usually around 13.2V-13.5V).
happy john
Member
Matt, I have a Anderson plug wired direct to my aux and the ability to plug in my 240 volt charger to maintain it only. A bit simpler than your idea and more effective. So far I've never had to use it apart from an overnight test.
^ and that's a great way to do it. Charger sees ONE battery and takes care of it. Battery will last longer!
Yep that is a fair point. I know it is not good to charge the aux battery with the 240v charger while the CTEK is still connected, have learnt that the hard way. I don't understand why the AUX battery will not get a full charge while the 240 charger is hooked up to the main battery, does it not just mimic an alternator?? Or am I missing something here?
I never see my CTEK push 14.4 volts into my AUX battery. Does this seem normal?
I never see my CTEK push 14.4 volts into my AUX battery. Does this seem normal?
happy john
Member
So hard to diagnose a problem like this it could be a multitude of things causing such an issue. I would look firstly at the battery and see if it has seen better days. Even if it is not that old a problem would mean that it will never accept a full charge, nor get to the 14.4 that it should. Have you another battery you could perhaps swap over and repeat the test?, or you could get the existing one tested. That would be a simple start.
Thanks John, yeah I guess I could get it load tested, however when I hookup my 240v charger to it, it will take a full charge everyday of the week and it will hold a full charge no problem. Will power my fridge and other accessories for 4 days until it needs a charge again. I guess the CTEK is only a 20a charger at the end of the day. I don't drive my ute all that much/far these days, I would just think if the battery needed it, it would wack 14.4 volts into it right away but I never see it get above 13.2 volts.
The alternator is designed (and regulated) to charge the starter battery with about 14.1-14.4V. To fully charge a lead acid battery in a short period of time you need to give it something like 15V.
The cable between the starter and aux batteries introduces the actual problem for both the alternator and the 240V charger connected to the starter battery. The starter battery gets up to voltage and the charger thinks it's full. Because of voltage drop across the cable, the aux battery isn't getting anywhere near full unless the CTek charger is down near that battery and is only charging that battery. When it's just a cable (with or without isolator), you might see 14.4V at the starter battery and only 13.1V at the auxiliary (typical for a 5m length of 6mm cable). Heavier cabling reduces the problem but it will always be there to a degree - so the aux battery won't fully charge in a hurry. It will - but could take many, many hours.
The most common (because it's reliable, effective and efficient) method is to let the alternator handle the starter just like it's always done, and make the CTek just another load on the end of a cable. That lets the CTek handle the aux battery. The starter will work like it's supposed to and so will the aux.
Quick note: a 20A charger doesn't always pump 20A into the battery. Power is delivered in accordance with how full the battery is - let's assume a 100Ah battery that's been discharged to 50%. It will start charging at 20A (bulk charging stage) until the battery approaches full, then it will switch to "absorption stage" where the amps are pulled back a little and the battery is allowed to "settle" with the charge it's been given and the remainder is brought up at a slower rate. Once full, the charger switches to "float stage" where it delivers around 13.2V and low current in a "maintenance" mode. This basically means that 50A won't be replenished in 2.5 hours like you'd think - it could take 3-4 hours.
The cable between the starter and aux batteries introduces the actual problem for both the alternator and the 240V charger connected to the starter battery. The starter battery gets up to voltage and the charger thinks it's full. Because of voltage drop across the cable, the aux battery isn't getting anywhere near full unless the CTek charger is down near that battery and is only charging that battery. When it's just a cable (with or without isolator), you might see 14.4V at the starter battery and only 13.1V at the auxiliary (typical for a 5m length of 6mm cable). Heavier cabling reduces the problem but it will always be there to a degree - so the aux battery won't fully charge in a hurry. It will - but could take many, many hours.
The most common (because it's reliable, effective and efficient) method is to let the alternator handle the starter just like it's always done, and make the CTek just another load on the end of a cable. That lets the CTek handle the aux battery. The starter will work like it's supposed to and so will the aux.
Quick note: a 20A charger doesn't always pump 20A into the battery. Power is delivered in accordance with how full the battery is - let's assume a 100Ah battery that's been discharged to 50%. It will start charging at 20A (bulk charging stage) until the battery approaches full, then it will switch to "absorption stage" where the amps are pulled back a little and the battery is allowed to "settle" with the charge it's been given and the remainder is brought up at a slower rate. Once full, the charger switches to "float stage" where it delivers around 13.2V and low current in a "maintenance" mode. This basically means that 50A won't be replenished in 2.5 hours like you'd think - it could take 3-4 hours.
Thanks Old Tony. It's all a big learning curve for me, but I am enjoying it none the less. I have my battery setup like you mentioned. So the starter battery is done with alternator and aux done with the CTEK. I am running a large 10mm cable just under 4m run. I understand it will still be getting voltage drop, it's bugger all though all things considered. I'm getting 13.3 at the starter battery and 12.9 at the aux.
happy john
Member
Matt never run your fridge and all the other bits for 4 days without putting charge back in as soon as you can.
happy john
Member
This is very well explained by Tony Matt, have another read. If your battery is exhausted the CTEK will refuse to quickly charge it. Best to keep it topped up. Before I had solar I would idle for 15mins twice a day.
Yep when I say that it runs for 4 days it does get started every so often for 15 - 20 mins. I get what Tony is saying to a degree. I have had it on the charge all day and it is charging at 14.2 volts as I type this. Next thing on my list is definitely going to be a 120w folding portable solar panel. What do you guys think of the projecta multi fold out panel, at $800 it seems dear, but you get what you pay for I assume? Thanks again.
happy john
Member
I now have to do a 200km trip quickly for some idiot that needs help tony will assist matt
