Do I (Does anyone?) Need A Second Battery Isolator?

Submitted: Monday, Feb 04, 2008 at 18:42
ThreadID: 54234 Views:2476 Replies:4 FollowUps:6
This Thread has been Archived
I have just finished setting up my Prado with an auxiliary battery and heavy cabling via an Anderson plug to the van battery, as per this link.

I have used an electronic battery isolator between the car battery and the auxiliary battery (in the car), which, I understand, ensures that charge from the alternator goes first to the cranking battery until it is charged, then to the auxiliary battery.

Following that logic, shouldn't there then be another battery isolator between the auxiliary battery in the vehicle and the caravan battery? This would ensure that the charge would go to the cranking battery until it was full, then to the auxiliary battery until it was full and finally to the van battery.

It seems to me you might need this if the auxiliary battery was flat and the van battery nearly full, or vice versa because without an isolator the two batteries are just connected in parallel and the flat battery will just drag the fuller one down, requiring BOTH batteries to be re-charged and having to share the charge from the alternator. That seems to me to be pretty inefficient.

Wouldn't it be better to have a second electronic isolator to direct the charge between the vehicle auxiliary battery and the van battery, just as the first isolator directs it between the cranking battery and the auxiliary?

But I haven't seen or heard of this, so is there a reason it's not done?

Cheers

FrankP

Lifetime Member
My Profile  My Blog  My Position  Send Message
Moderator

Back Expand Un-Read 0 Moderator

Reply By: Mainey (wa) - Monday, Feb 04, 2008 at 20:23

Monday, Feb 04, 2008 at 20:23
frank,
there are many possible answers to this question, some are ‘better’ than others and I say that in the nicest possible way.

The most likely battery to go flat first is the last in the chain which is in the caravan, because it's probably got the highest draining products to run, and IF it has a vehicle activated battery ‘isolator' between it (3rd battery) and the 2nd battery, it will ONLY recharge or connect to the second battery when the vehicle is running.

OR:

If the 'battery isolator' is a MANUAL SWITCH it will only equalize the 2nd & 3rd battery when the switch is set to connect the 2nd and 3rd battery in parallel together, even when the vehicle is not running it will equalize the two batteries (or it will keep them separated if required)

The two batteries, now in parallel, or only the 2nd battery will recharge ONLY when the vehicle is started after the Cranking battery is fully charged.
The benefits of a "larger" house battery system is they both will only partially discharge when connected together, whereby a single battery will discharge much further, greatly diminishing it's life span.


The use of 'quality' AGM Deep Cycle batteries will be very beneficial to your system because they charge deeper and much faster than wetcell batteries.

Mainey . . .
AnswerID: 285625

Reply By: Member - Peter R (QLD) - Monday, Feb 04, 2008 at 20:33

Monday, Feb 04, 2008 at 20:33
Could not get your link to work.

Not qualified in any way but my set up is along these lines
.
Cranking battery is connected through a Redarc to charge second battery in back of vehicle., when ignition is switched on.
Wiring for this second battery is then piggy backed through to Anderson plug at back of car and connects to van via Anderson plug.
The anderson plug on van connects to battery in van. Van battery will only be charged when iginition is on.

My understanding is that the 2 batteries charge after cranking battery has sufficient and not before.
I previously ran fridge in van via normal 7 pin plug but was not happy with result and if i forgot to disconnect 7 pin plug at a lengthy stop I stood the chance of flatening the cranking battery.

Now with the van battery charged through anderson plug I have the fridge connected to van battery to charge it while travelling.
Have used a "frige stop??" which turns off the current to fridge when van is stationery for around 3 minutes.
This way van battery will not go flat while stopped and 7 pin plug /anderson plug now is not connected.

Works well for me.

Pedro

AnswerID: 285627

Follow Up By: Mainey (wa) - Monday, Feb 04, 2008 at 20:48

Monday, Feb 04, 2008 at 20:48
Pedro posted:-> ""Have used a "frige stop??" which TURNS OFF the current to fridge when van is stationery for around 3 minutes.
This way van battery will not go flat while stopped and 7 pin plug /anderson plug now is not connected""

So how do you power the fridge if you go into the shopping center for a quick coffee, which may take (me) an hour or so lol

Mainey . . .
0
FollowupID: 550623

Follow Up By: Frankp - Monday, Feb 04, 2008 at 21:35

Monday, Feb 04, 2008 at 21:35
Peter,

Thanks for your response.

This link should work. Dunno what happened to the last one.

Frank
FrankP

Lifetime Member
My Profile  My Blog  My Position  Send Message
Moderator

0
FollowupID: 550652

Reply By: Member - Peter R (QLD) - Monday, Feb 04, 2008 at 21:22

Monday, Feb 04, 2008 at 21:22
Mainey,
I was told by experts that if the fridge is not opened it will not lose much in temperature.
This seems to be the case, and we had no problems during recent trip to SA.

If you had fridge running off the battery without battery being charged you stand a good chance of the battery being flattened.

The battery I have in van is a 40a AGM.

Pedro
AnswerID: 285646

Reply By: Frankp - Monday, Feb 04, 2008 at 21:54

Monday, Feb 04, 2008 at 21:54
Mainey and Peter,

Thanks for your responses.

The way my set-up is at the moment, the aux and the van batteries are in parallel via the Anderson plug and the fridge, when on 12v, runs off the van battery.

Because the two batteries are in parallel there's a good few hours capacity to run the fridge when parked, though if I figure that our "few minutes stop" is going to be over an hour I'll change to gas, then back to 12v when we get going again.

My main concern is when we're camped, when it's likely that the van battery will run down. I have a solar panel (fixed to the van) but they're always subject to weather, shade, orientation, etc, so cannot always keep up with demand.

Therefore it's quite possible for the van battery to be significantly discharged, while the vehicle aux battery is fully charged. It seems to me to be better in those circumstances to have a second isolator direct charge to the battery that needs it, the van battery.

The alternative would be to leave the car and van connected via the Anderson plug to parallel the batteries and share the load, but then requiring extended charging time to charge the two paralleled batteries.

But I prefer to have the van battery do its work running the camp, leaving the vehicle's aux battery always as a fully charged reserve just in case Murphy visits, which he often does! Then charge the van battery as needed.

As I said, I haven't seen or heard this discussed. Is there a technical reason why it's not done?

Frank
FrankP

Lifetime Member
My Profile  My Blog  My Position  Send Message
Moderator

AnswerID: 285659

Follow Up By: Member - Peter R (QLD) - Monday, Feb 04, 2008 at 23:12

Monday, Feb 04, 2008 at 23:12
I have pretty well the same set up and , as you say , if I am not running car for a while run the van fridge on gas.

I also can charge the van battery , through my Ctek 7000 which has been modified to connect to wiring by Anderson Plug on van,
The Ctek also charges my car auxillary battery via the Anderson plug on back of car.
Not at the same time of course , and only when 240 v available.

To conserve your van battery while camping why not use gas, and the battery just for lights?


Pedro
0
FollowupID: 550678

Follow Up By: Frankp - Monday, Feb 04, 2008 at 23:27

Monday, Feb 04, 2008 at 23:27
>>To conserve your van battery while camping why not use gas, and the battery just for lights?<<

I do that, Pedro.

I'm just trying to figure out the best battery management/recharging system for the van battery.

I like the idea of the Ctek charging the aux battery via the Anderson plug. Obvious when you think about it, but I hadn't thought about it!!

Frank
FrankP

Lifetime Member
My Profile  My Blog  My Position  Send Message
Moderator

0
FollowupID: 550679

Follow Up By: Mainey (wa) - Tuesday, Feb 05, 2008 at 09:44

Tuesday, Feb 05, 2008 at 09:44
I personally think a 40ah battery is far too small in capacity to be able to be relied upon for a reasonable storage battery system !

I'm sure you will find most guys will use a minimum of 80ah and many use well in excess of 200ah.

The lower you discharge a 12v battery, the longer it takes to recharge and with more chance of battery damage occurring, by comparison a similarly discharged 100ah AGM 12v battery will recharge faster than a 40ah wetcell battery.

Stated very simplistically:
Remembering a 12v battery should not be constantly discharged below 50% of it's rated capacity, in the case of a 40ah 12v battery you have only the equivalent of running 1 x Engel/Waeco etc for just one day
(2.5ah x 8 hours = 20ah)

Mainey . . .
0
FollowupID: 550727

Follow Up By: Member - Peter R (QLD) - Tuesday, Feb 05, 2008 at 10:56

Tuesday, Feb 05, 2008 at 10:56
Thanks Mainey,
The 40a battery is there just as a back up, as we normally stay in powered parks.
Would definitely get a larger battery if using for camping.

My Waecos' CF50 & CF18 remain in back of Prado and I have a 120aAGM battery feeding them and battery is charged via Ctek (through Anderson plug) , with a double adaptor running the larger Waeco and Ctek when 240 available.

Using van battery to run the fridge , while travelling, with the "stop fridge" is much better than having to get out and remember to disconnect the 7 pin plug.


Pedro
0
FollowupID: 550736

Sponsored Links

Popular Products (14)