Deep cycle battery setup

Submitted: Thursday, Nov 14, 2019 at 14:35

ThreadID: 139323 Views:7245 Replies:4 FollowUps:9

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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.

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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

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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.