Discharging batterys reply

Thanks guysa for all the info. The dual batts are in parallel so big amps and 12v. The smart relay is only ment to opperate when main batt is at 13.7v. Odd thing is while running the volts at the batt + only get just under 13v so it should not work at all. With the two systems disconected both batterys still dropped from about 12.8 to about 12.6, maybe one bad batt has dragged them all down. Might ditch one of the deep cycle and replace main. I have booked in a auto electrician and will get an alt test. Also my main connection between the two is very heavy duty wire and I have seen one set up last week with very light wire. Oh well the auto will sort it out. $$$$ I just dont want to go flat in the Flinders. Thank you.

Philip

Wise move dude.
as you say, getting stuck out there is not my idea of having fun.
keep us posted as to what actually is amiss.
best of luck
l8tr
E

Best of luck with Your trip...
Let Us know what the auto electrician says caused the problem....


Lee

Best of luck with the autoelectrician.

All the wire gauge really affects is the charge rate. I have fairly narrow gauge wire so I don't overload my already borderline charging system.

General_Failure wrote:Best of luck with the autoelectrician.

All the wire gauge really affects is the charge rate. I have fairly narrow gauge wire so I don't overload my already borderline charging system.

err, that theory isn't quite right...

oh, it's not? guess I got some bad info then.

The problem with a thin wire is that with a fast charge rate a thin wire can overheat! So go with a thick wire: this is a high-current situation and so you need a wire with low resistance: thicker is better.

I had a smart relay between my kombi's main and aux batteries, it worked for a couple of days and then died. I replaced it with a big high-current simple relay from a caravan & boat accessories shop and it's worked perfectly ever since. The makers of smart relays claim that their advantage over a simple relay is that the smart ones prevent very high current when the aux is totally flat. Personally I'd rather have a simple relay that works (and a very thick wire) than a smart one that doesn't.

What year is your kombi? The late bays have good alternators that produce 70 amps which gives plenty for recharging an aux if you're not pulling power for lots of other things e.g. spotlights, stereo etc all at the same time.

There is a very good article on dual-battery setups here: read it, and go with suggested Option 3, it's reliable and it works!
http://www.aussiekombicampers.com/projects_cebm.shtml

Purple Martin wrote:. The makers of smart relays claim that their advantage over a simple relay is that the smart ones prevent very high current when the aux is totally flat.

Smart relays simply disconnect the aux battery from the working (cranking) battery VIA a heavy duty relay, (built in) if the entire system voltage drops below a preset figure.
(for the life of me i cannot remember what it is exactly).
The pull-in coil of the relay is electronically controlled. But, the relay is a simple relay.
The smart relay will not re-connect the aux and working batteries until the working battery system voltage rises ABOVE a preset figure which is significantly HIGHER than the original disconnect voltage.

Much the same can be achieved with a simple relay but you dont get the extra aux capacity of the addition of the two batteries together.
Another thing to consider when charging batteries in parrallel is that the alternator will not necessarily "look" at the flat aux battery nor the charged working battery. The alternator "sees" something quite different.
I cannot remember exactly what the alternator actually "looks" at now, but the end result is the entire system having greatly reduced capacity unless the alternator is actually switched from one battery to the other or a third party charging system is used on the aux battery.
This was the problem facing my M8 when we fitted a 1300watt pie oven into a mobile food van and powered it using a 1800w 12Vdc/240Vac inverter. It drew about 110 amps continuous.
We used a really big arsed marine deep cycle aux battery and a smart relay but the deep cycle battery kept going flat after about 40 minutes.
In the end we made 2 x 85amp alternators work together for a combined output of 160 amp (was not able to fit any bigger alternator due to space) in conjunction with a smart relay. One alternator "looked at the aux battery and the other "looked" at the running battery.
Conversation came up with the auto-elect about parralleling and charging of batteries and its not as straightforward as it appears to get them to work together efficiently, when one of them is designed to disconnect from the other and end up with voltage differences, and to then charge them up equally.
My head hurts now.
L8tr
E

Wow, two alternators, that's cool! I'd love to see how you did that, have you got any pics?

The smart relay I had used mofsets for switching, and it definately claimed to prevent very high current when charging a totally flat aux, so I stand by what I said before.

i made one of those smart relay set ups for my old mans ute but he hasnt got around to wiring it up yet

Purple Martin wrote:Wow, two alternators, that's cool! I'd love to see how you did that, have you got any pics?

The smart relay I had used mofsets for switching, and it definately claimed to prevent very high current when charging a totally flat aux, so I stand by what I said before.

yer, I can accept that iffen its made that way. Thats a particularly smart relay dun you think. It makes sense to limit the charging current on a flat battery to improve battery life thats for sure.

Sadly, I have no pix of the dual alternator job. That van was sold recently.
I had to fabricate a new bracket which I placed in the A/C compressor mount position and we got an old power steering pump pulley from the wreckers, machined the guts out of it and welded it to the original front pulley as we were unable to get a genuine twin row pulley.
Both bloody alternators went close to stopping the engine when the oven kicked in tho!!!!!
l8tr
E

Purple Martin wrote:The problem with a thin wire is that with a fast charge rate a thin wire can overheat! So go with a thick wire: this is a high-current situation and so you need a wire with low resistance: thicker is better.

I had a smart relay between my kombi's main and aux batteries, it worked for a couple of days and then died. I replaced it with a big high-current simple relay from a caravan & boat accessories shop and it's worked perfectly ever since. The makers of smart relays claim that their advantage over a simple relay is that the smart ones prevent very high current when the aux is totally flat. Personally I'd rather have a simple relay that works (and a very thick wire) than a smart one that doesn't.

What year is your kombi? The late bays have good alternators that produce 70 amps which gives plenty for recharging an aux if you're not pulling power for lots of other things e.g. spotlights, stereo etc all at the same time.

There is a very good article on dual-battery setups here: read it, and go with suggested Option 3, it's reliable and it works!
http://www.aussiekombicampers.com/projects_cebm.shtml

Thats where I got the info for my setup from, and its a 74 model. Can't vouch for the engine year model but I believe its the same.
At night the alternator wept. High beam 2x100w + 100w? driving light. It'd be just enough to start bogging down the electrics.

Dual alternators? cool. Reminds me of that ex swiss(?) army splitty I saw in a mag ages ago. It had a generator stalk with two mounts on it.

General_Failure wrote:At night the alternator wept. High beam 2x100w + 100w? driving light. It'd be just enough to start bogging down the electrics.

Volts x Amps = Watts

so

200W / 12V = 16.7 amps

Your high-beam lights are only drawing 16.7 amps, your alternator has a 70 amp output... what else did you have running that was using a lot of current?