Charging the aux batteries off the alternator

Ziggy99 · Member

Charging the aux batteries off the alternator

Jaahn · Guru

Hi Ziggy smile

The answer is the computer is programed to replace the starter current which is normally not as much as you might think. It tops up the battery for a time monitoring the voltage. After if deems the battery full then it drops the voltage, as everthing else in the car can use lower voltage down to around 12v OK. The alternator then just supplies the current that the car uses forever at the low voltage. This reduces the power required. confuse

I do believe some cars can have this facility turned off by a dealer service tool but I have not actually seen this done. You already know that this is the reason for the DC to DC chargers that are now available for charging the van batteries. hmm

Jaahn

patrol03 · Senior Member

What vehicle are you referring to Ziggy,and do you mean your alternator is capable of 130 Amps ?

PeterD · Guru

Agreed, we need to know more of what you have. As well as the vehicle make model and year model, what size cable are you using in both the tug and van in conjunction with your Anderson plug? What is the voltage at the tug battery when you are reading 13.7 V at the alternator? What cable lengths are do you have to the Anderson plugs in the van and the tug?

macka17 · Guru

How are you connecting second battery?.

Normally people use a dual battery controller connected to battery of car.
wired through from there to second battery (wherever) with decent cable dia to suit.

Usually use Normally charging, NOT starting cable from main batt to controller.
then again from there to second battery.
OR Starting cable from there, IF you intend to use second battery as a starter supply if main dies

The Controllers normally take main battery up to 13.4v (some adjustable)
then transfer charge current to second battery at whatever rate it set for(they vary).
Solenoid units usually a fixed trip over voltage. Electronic ones (mine) variable.

They also Normally. have a kick in contact sw to charge second as well as primary batt if wanted, earlier.
from time you touch that switch.
Or on\off if solenoids under the bonnet.

Elecrtronics\electrics can be dangerous if you have to ask what's what.

If you don't know the principals of doing it properly.
I'd suggest contacting somebody who does know.
and maybe install a proper controller. Preferably an electronic one,
the Solenoid units never give full charge b4 switching.

Apart from anything else.
You won't be buying battery's so often.

Peter_n_Margaret · Guru

It is all about cable size, voltages and internal battery resistance.
Our 85A alternator with an output of 14.3V can direct charge the AGM house batteries at up to 70A when they are low, less as they fill up.

Cheers,
Peter

macka17 · Guru

That's the reason for the Electronic Controllers Pete.
They can take second bank. primary battery's too, to max.
ALL the time.

Providing the cables etc are to suit.

You not a sparky and want it to work properly. FROM THE START.?

Don't ask blokes driving caravans and read a coupla books

See a sparky and get it done right the first time hey.

Advice is welcome for 90% of things in this game. We've all done some.

But the serious stuff. Electrical. wiring. brakes etc.

Ask the real experts. They been trained for it.

Apart from saying always get thicker cable. My advice is always the above.
On those items.

Peter_n_Margaret · Guru

In my experience sparkies know very little about this stuff.
If the alternator is supplementing solar, then it is not necessary for it to achieve 100% SOC, although mime will, easily. The solar will finish the top up.

Cheers,
Peter

Ziggy99 · Member

Thanks folks.

As I said, when the batteries were drained to 11.5 v for the test the alternator could deliver 19 amps to the Anderson and 13.7 volts to the batteries. To the input side of the smart controller it supplied 14.1 v. So it was never going to provide a bulk charge.

Reading around the topic I found one RV sparky reckon that most aux batteries only ever get to 70% SoC.

Jaahn, are you referring to a so-called smart alternator? Mine isn't one of those.

And yes, the solution was to replace the isolator with a DC-DC charger and to add solar on camp days.

I still don't know how much the vehicle running was consuming. Certainly if the alternator settles to 12 v that's going to undermine the whole game.

Along the way I also found the fridge was drawing 2 X or more than the advertised figures. Grr.

PS 0.4 v loss from isolator in the original setup to batteries is exactly what a voltage drop calculator predicts.

-- Edited by Ziggy99 on Sunday 26th of February 2017 03:56:23 PM

-- Edited by Ziggy99 on Sunday 26th of February 2017 04:20:20 PM

Jaahn · Guru

Ziggy99 wrote:
Thanks folks.

As I said, when the batteries were drained to 11.5 v for the test the alternator could deliver 19 amps to the Anderson and 13.7 volts to the batteries. To the input side of the smart controller it supplied 14.1 v. So it was never going to provide a bulk charge.

Reading around the topic I found one RV sparky reckon that most aux batteries only ever get to 70% SoC.

Jaahn, are you referring to a so-called smart alternator? Mine isn't one of those.

And yes, the solution was to replace the isolator with a DC-DC charger and to add solar on camp days.

I still don't know how much the vehicle running was consuming. Certainly if the alternator settles to 12 v that's going to undermine the whole game.
Along the way I also found the fridge was drawing 2 X or more than the advertised figures. Grr.
PS 0.4 v loss from isolator in the original setup to batteries is exactly what a voltage drop calculator predicts.

Hi Ziggy smile

Yes I was referring to a smart alternator !! If you do not have one of them, then your system is certainly stuffed furious I believe there are some other alternator systems which reduce the voltage too, not only the "smart ones". I have an early Sprinter motor home, with an 120A alternator. I have the aux battery in the far back so about 5+ meters from the front battery and alternator. There is a very LARGE cable connecting the two batteries with body earth return. A VSR does the switching at the battery end.

I can recharge my 150Ahr battery in a short time when I start the engine. I have never measured the current as I have not needed too, half an hour tops it up. I have a volt meter on both batteries inside so I can see what is happening. If I drive every day the house battery is ALWAYS FULL. wink The two small solar panels on the roof hardly do anything if the motor is run.

You have not told us what vehicle and model you have !

Jaahn

-- Edited by Jaahn on Monday 27th of February 2017 09:18:01 AM

macka17 · Guru

I was refering to a Car or better still. A MARINE 12v sparky. Sorry.

The best way I've found to keep all my battery's on van. car. and boat topped up full.
Is to have a panel and regulator on the roof of.

My car, and the 2 Aux batt's in tray are always sitting on 13.2 ish on Scanguage\multi.
Has 80w Panel on roof bars with roll out.

Boat batt's the same. 40 and 80w panels on carport.

Caravan has smart 10a Charger plugged in at present. Normally the 200w panel on roof.
with 13.2ish v.

That, and\or an adjustable Smart dual controller in car are the proven best way to do it.
With, or without engine running.

SUN shining. you'll always sit on float (13+v)with any battery's.

The only practical way nowadays. Specially with the fallen costs of panels.

Jaan.

The panels are there for float really, and usage when sun falls out of sky.
If you take reading of battery with panels in line. then again following day with panels disconnected.
you'll read round about 12.7ish without. and 13.2ish with panels on float.

It also makes a change to battery life too.
from 2 1\2 to 3 yrs. To 6 plus yrs.

My boats averaged 7 yrs with panels and Exide Extremes in line.
NEVER on mains charge.

There's no reason nowadays NOT to have at least one float panel up there
to guarantee battery level and life.
They cost virtually nothing.

John Kay · Veteran Member

Hi Ziggy, My comment is only for charging the batteries only. If you were to connect them via a Cteck 250s control unit it would make sure your starter battery is fully charged before charging the aux battery. Hope it gives you something to look into. Cheers.

PeterD · Guru

Ziggy99 wrote:
1.. As I said, when the batteries were drained to 11.5 v for the test the alternator could deliver 19 amps to the Anderson and 13.7 volts to the batteries. To the input side of the smart controller it supplied 14.1 v. So it was never going to provide a bulk charge.
2.. Along the way I also found the fridge was drawing 2 X or more than the advertised figures. Grr.

1.. You are not making sense here. First you over discharged your batteries for the test, 12.2 V would have been sufficient. Batteries do not accept a vary high charging current when nearly flat. What is the smart controller you are talking about? Is it, is it just a dual battery isolator? If it is a dual battery isolator, you are getting 14.1 V into your controller, the battery is only drawing 19 A and only 13.7 V at the battery being charged, this means your wiring is woefully undersized.

I asked you several questions including the size of wiring but you did not answer them. If you don't supply the info we require. Do you really want your problem solved?

2.. Fridges are often specified with the the average current drawn by them. Fridges work on an off/on cycle. When the sealed unit is operating they draw their maximum current. When in the off part of the cycle they draw nothing. If the unit runs for 50% of the time the average current is half the maximum. You are probably confusing average current with the current drawn when th unit is running.

swamp · Senior Member

HI
Ziggy
One of the first to test the ando under load ,you are to be commended.!!!!!
Basically 12.volts =50% standing volts 19 amps current draw would more likely be around 20-30% approx. 12.4volts standing
[I have regular 30amp draw when battery agm 120ah is around 50% discharged]

Recharging at 19 amps and having a voltage of say 13.7v
13.7 is the absolute min for recharging batteries in a **** reasonable time *******
Its exponential dropping down to 13.5v doubles /quadruples charge time
Any further current draw by the batteries will drop the volts which is bad news
But at least you no that at 19 amps its charging ok
THATS WHY USE BIGGER OR HUGE CABLE IS ALWAYS RECOMMENDED to keep the volts up