Split charge -feed from alternator warning light or ignition

Post by **deeja** » 05 Jun 2007, 22:16

Hi
I'm just about to wire up a split charge unit in my T25 TD and connect my relay to the blue wire from my alternator (behind the fuse box), when I noticed this on the wiki:

"pick up the relay feed from the ignition instead of the warning light"

So where exactly does this refer to?

Any help would be appreciated before I burn out my wiring loom...

Regards
D

Post by **R0B** » 05 Jun 2007, 22:21

does this help...
[IMG:500:612]http://img.photobucket.com/albums/v211/ ... Charge.jpg[/img]

Post by **jason k** » 06 Jun 2007, 07:38

if you use a "smartcom" from towsure or the like you dont need the alternator feed as it automatically senses when to switch charge. and they are only twelve quid!!!! much easier!!!

Post by **Hacksawbob** » 06 Jun 2007, 07:47

thanks jason wiki'd that.

Post by **Mocki** » 06 Jun 2007, 14:59

jason k wrote:if you use a "smartcom" from towsure or the like you dont need the alternator feed as it automatically senses when to switch charge. and they are only twelve quid!!!! much easier!!!

dont go there..... they are designed to be in a caravan set up, and will proove unreliable....... and three times the price of a simple relay.......

switch from the alternator if you can, its the best way.

Post by **holy-mojo** » 06 Jun 2007, 15:26

I've wired up my split charger to this drawing and have noticed that the "no charge" warning light glows very slightly (only visible at night). This was true both with and without the leisure battery installed. Would switching the relay draw too much current from this circuit on the alternator (it is a large 200 amp relay - for a big stereo)? I've heard that if the no charge warning bulb is blown it prevents battery charging (on early 924s) so glowing may have an influence on charging. Could this glowing explain my flat battery the other day after leaving the van standing for a week?

Post by **jason k** » 06 Jun 2007, 16:00

Mocki wrote:
jason k wrote:if you use a "smartcom" from towsure or the like you dont need the alternator feed as it automatically senses when to switch charge. and they are only twelve quid!!!! much easier!!!

dont go there..... they are designed to be in a caravan set up, and will proove unreliable....... and three times the price of a simple relay.......

switch from the alternator if you can, its the best way.

been absolutly fine in my bus. easier to wire too. you pays your money and takes your choice i suppose!!!

Post by **Mocki** » 06 Jun 2007, 16:01

jason k wrote:
Mocki wrote:
jason k wrote:if you use a "smartcom" from towsure or the like you dont need the alternator feed as it automatically senses when to switch charge. and they are only twelve quid!!!! much easier!!!

dont go there..... they are designed to be in a caravan set up, and will proove unreliable....... and three times the price of a simple relay.......

switch from the alternator if you can, its the best way.
been absolutly fine in my bus. easier to wire too. you pays your money and takes your choice i suppose!!!

one wire different.. how much easier is that!

Post by **deeja** » 06 Jun 2007, 16:16

Thanks
Yes the diagram does help and confirms what I thought...
The wire from Term 86 going to the cable which runs from my alternator to the charge light (Which I believe is the solid blue wire behind my glove box).

sukhoi27 wrote:does this help...
[IMG:500:612]http://img.photobucket.com/albums/v211/ ... Charge.jpg[/img]

Post by **vanjam** » 06 Jun 2007, 21:39

holy-mojo wrote:I've wired up my split charger to this drawing and have noticed that the "no charge" warning light glows very slightly (only visible at night). This was true both with and without the leisure battery installed. Would switching the relay draw too much current from this circuit on the alternator (it is a large 200 amp relay - for a big stereo)? I've heard that if the no charge warning bulb is blown it prevents battery charging (on early 924s) so glowing may have an influence on charging. Could this glowing explain my flat battery the other day after leaving the van standing for a week?

I think the the relay draws some current thereby disturbing the (ideally) balanced voltage between the battery and alternator terminal hence your light on low or flickering. If occasional or very low level flickering the charge should be ok but the hugeness of your relay maybe significant.

Have you measured the charging voltage when the light is on?

There is an electronic fix to this with some diodes on www.kampenwagen.???? I think. not clear if your bulb is broken or not but I'm trying to think why this would stop charging. All the light does is monitor the voltage balance between the battery live and the alternator B+ terminal. If that circuit is broken, no current is flowing in the warning circuit so your split charge relay would remain closed and I can't think why the alternator would stop charging simply due to the loss of this circuit-but I stand to be corrected.
Cheers

Jim

Post by **Willoughby** » 07 Jun 2007, 16:32

The benefit of the Smartcom is that it has a bit of intelligence. It monitors the voltage of each battery and supplies the optimal charging current to each battery. It come it to its own when there is a large difference between the two battery voltages. (ie flat LB).

Im not knocking the split relay charging method it works fine and I like the keep it simple approach. but the Intelegent charging relays like the smartcom are a step up from the basic method.

Kev

Post by **tonytech** » 07 Jun 2007, 16:44

IIRC.
The charging light supplys a current to the alternator.
The small current excites the coils in the alternator.
The excited coils provide the magnetic field for the moving bits to generate electricity.

There should be a resistor paralleled withe the bulb so a duff bulb wont stop the charging process though.

T

Post by **holy-mojo** » 08 Jun 2007, 11:34

Thanks for the info. I'll try and wire up a voltmeter to monitor the charging voltage during running. I believe the light is on constantly, just not visible in daylight. At idle I measured 13.5 volts so the alternator is doing something. Am I correct in assuming that if the voltage supply is up to 14.5 volts, then the alternator is charging? Could the current output of the alternator be restricted even though the voltage is at the correct level?

I've just received my new Varta leisure battery so this should tide me over for a long weekend even with poor charging.

The issue of non-charging with a blown bulb - just heard it from a friend with a 924. Apparently it is a known problem with them.