Deep cycle battery setup
Submitted: Thursday, Nov 14, 2019 at 14:35
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Joao M1
Hello everyone.
I am on a WHV in this beautiful country and I just bought a car which I want to equip. I understand electronics and all that, but still I would like to hear your opinion on a deep cycle battery setup.
I am aware that AGM batteries behave differently from lead acid ones and that the best way is to have a DC-DC charger on the car to charge it. I do not not want to go that way due to budget reasons.
I would like to know if it is too problematic to charge it from the alternator considering the following:
- There will be an insulator for this 2nd battery to isolate it from the main battery and alternator when the car is off
- I will have a solar panel with controller, so when the car is stopped it will be properly charger
- Load will be really low. Only a laptop, 2 phones and a camera, and maybe a small fridge.
I am aware that most of the times the alternator won't be able to 100% recharge an AMG battery, but I am fine with that as long it keep's it at a reasonable charge and I will charge it most of the times with solar.
Thank you for your help.
Reply By: MickeyJ - Thursday, Nov 14, 2019 at 15:40
Thursday, Nov 14, 2019 at 15:40
Hi,
Battery Isolator should work OK depends on the vehicle. Main reason for DC DC chargers these days is that the modern vehicle designs do not want to charge a second battery. They sense the load on the car and stop charging not aware that their is a second battery.
Cheers
Mickey
AnswerID:
628662
Follow Up By: Joao M1 - Thursday, Nov 14, 2019 at 15:46
Thursday, Nov 14, 2019 at 15:46
I am aware, but nor worried about that. I am not use the car alternator is smart, but if it is I will just unplug the sensor and force it to charge.
FollowupID:
903109
Follow Up By: RMD - Thursday, Nov 14, 2019 at 17:35
Thursday, Nov 14, 2019 at 17:35
Joao M1
Unless you understand the intricacies of Can Bus control of the alternator you may not be able to simply “unplug” the sensor. It detects current flow to initiate charge, not to turn it off.
FollowupID:
903113
Follow Up By: Joao M1 - Thursday, Nov 14, 2019 at 21:11
Thursday, Nov 14, 2019 at 21:11
Yes, I know, but by unplug it it won't be able to measure the current, so it will act as a normal alternator, shutting off when it gets too hot.
FollowupID:
903116
Follow Up By: RMD - Saturday, Nov 16, 2019 at 11:45
Saturday, Nov 16, 2019 at 11:45
Joao M1
Do you know for absolute certainty that unplugging the sensor will make it charge?????
I suspect it doesn't work that way and if it did, by now, everyone who has a smart alternator would simply unplug the sensor and the large DCDC Charger market would not exist, because there would practically be no need for them.
If it cannot detect battery load then it would not charge to make up what it cannot "see", ie, little or no output form alternator.
FollowupID:
903148
Follow Up By: Allan B (Sunshine Coast) - Saturday, Nov 16, 2019 at 12:56
Saturday, Nov 16, 2019 at 12:56
.
Joao,
From the published wiring diagrams for your car, it does not have a voltage-controlled (smart) alternator so as Gbc has said, you should be able to charge your auxiliary battery via a simple isolator relay which can be either voltage sensing or simply a relay controlled by the ignition system.
If however it was a voltage-controlled alternator, and as has been said here by other contributors, you cannot simply "just unplug the sensor" to over-ride the alternator voltage control system. Doing so will ensure that the alternator will operate at minimal output and furthermore, such action may cause a "fault signal" to the Engine Management System and even place the vehicle in "limp" mode.
FollowupID:
903150
Reply By: Frank P (NSW) - Thursday, Nov 14, 2019 at 16:25
Thursday, Nov 14, 2019 at 16:25
You sound like you know what the issues are .
I presume "insulator" means "isolator". Autocorrect strikes again? :-)
If you can make sure that the alternator/system voltage is in the conventional range (ie, not "smart" voltages) then I think you will be ok with a conventional isolator-based system.
A couple of questions that may be helpful in the discussion:-
What is your vehicle (so those who know can determine the alternator/system voltage)?
What size (watts) solar panel?
Cheers
AnswerID:
628663
Follow Up By: Joao M1 - Thursday, Nov 14, 2019 at 16:33
Thursday, Nov 14, 2019 at 16:33
Yes, writing on the phone causes this :p
X-Trail T30 2.5l.
Solar panel is 120w.
FollowupID:
903111
Follow Up By: RMD - Thursday, Nov 14, 2019 at 21:05
Thursday, Nov 14, 2019 at 21:05
It is called Auto Mistake. For anything which is technically related it defaults to what it thinks. Turning OFF PreDicktive text fixes many issues.
FollowupID:
903115
Follow Up By: Gbc.. - Friday, Nov 15, 2019 at 09:23
Friday, Nov 15, 2019 at 09:23
That model xtrail looks to have an older style alternator. You will be just fine with a voltage sensitive isolator and a solar panel, especially for the time you are here. Enjoy the trip.
FollowupID:
903120
Reply By: phantom - Thursday, Nov 14, 2019 at 16:27
Thursday, Nov 14, 2019 at 16:27
Hi Joao,
Should be OK as I traveled for a few years using a 75Ah Thumper charging off the (not smart) alternator using a 140 W solar panel when camped up for a few days. This ran our 40L engel fridge, charged the laptop, phones, lights, camera etc.
Worst case was a couple of times we had to run the car for 30 mins or so when no sun for a few days.
AnswerID:
628664
Reply By: Joao M1 - Thursday, Nov 14, 2019 at 21:12
Thursday, Nov 14, 2019 at 21:12
Should I be worried about charging current? Like if it is too much for the battery?
AnswerID:
628666
Follow Up By: RMD - Friday, Nov 15, 2019 at 08:43
Friday, Nov 15, 2019 at 08:43
Joao M1
I ran a simple alt to constant duty solenoid (for isolation) and a very decent sized cable to a rear 105AH aux battery in a 60 series landcruiser for around 18 years. Because I made the solenoid feed originate directly from the alternator terminal, the aux saw that voltage which is slightly more than battery terminal voltage. Even when the aux is discharged a reasonable amount, it quickly builds up internal resistance, ie, opposition to current flow, and then settles and lowers as charge is achieved. It doesn't matter if you have a a 60 amp alt or a 150 amp alternator the current into the battery will be the same. Only near fully discharged will there be a fairly high flow of charge into the aux battery. I now do use a DC DC 25 amp unit but have all connections as Anderson plugs so if it gave trouble I can return it to the simple setup very easily.
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