Friday, 12 September 2014

Yamaha T-Max battery discharge solution

Those of us who have the Carburetor version of the TMax (2001 - 2005 IIRC) are likely to have a problem with the battery going flat frequently which I have discussed over here. I encourage you to read that older post to familiarize yourself with the problem, if you are not already familiar with it.

This is due to a strange design of the Auto-Chokes and powering them via a separate circuit independent of the ignition switch, directly from the battery. This results in the battery being discharged until the thermo switch has reached its low temperature cut off point.

The graph at left shows a simple EXCEL linear trend, this is however not the big picture with thermal equalization, as the drop in temperature will be slower as the difference between the heat of the item and the environment gets closer.

Meaning that this can take quite a while to get to the 55°C, especially on a hot day when ambient temperature is above 30°C, and even worse if you park it in the sun over hot tarmac. Essentially all this can easily keep the interior of the engine (where the switch measuring) above 55°C for up to an hour after you stop.

During this time the battery is having about an amp sucked out of it. Its of course made worse for your battery if you do multiple shorter trips during the day : so the engine gets hot in the 15 min of the trip, then the bike sits about sucking power out of the battery for another hour (and only charged for 15 min). This provides an increasing imbalance between charging and discharging.

Of course if I lived in a cold climate then the bike would probably cool in 10 min and it wouldn't be an issue ... but I don't


I proposed a solution to the problem in that earlier post (linked above) where a relay in circuit to isolate the Auto-Chokes when the bike was not turned on, and thus saving the battery from being drained, but still leaving the existing circuit (thermo switch circuit) untouched during operation.

The wiring for the auto chokes comes through the loom at this point (red square in image to left) and so I prepared a Normally Open relay which will then Close (completing a circuit and providing power) when the bike ignition is turned on.

Taking a close up from the full wiring diagram I've inserted the relay after the thermoswitch and before the auto-chokes.

So to do this I cut into the loom where the plugs for the auto-choke come out and inserted my relay in series into that circuit.

Getting into that loom and inserting that switch in series was a tight job. I prepared the relay with orange wires for the shunt to the additional switch and red and black wires for powering the relay.

I powered the relay by plugging into an existing plug on the loom under the fairing near the indicators, which was designed for accessory heated grips ... I'm not going to be using that particular option here ;-)

So with the colwings around the foot well taken off, you can get access to the loom and you can move the wire loom section from under the seat and open the loom up carefully with scissors to access the wires.

I've marked in green where I've run the 12V power leads up to the front of the bike where the accessory connector plug is located. I've run it along the 'breather' pipe to make it obvious where it is, and keep it from possibly rubbing against anything metal on the way (don't want any shorts now, do we) .

So with the relay wired in and the protective casings of the loom cable tied prior to wrapping with electrical tape we see it like this

note the two plugs facing us, they are the plugs for powering the auto chokes. My switch essentially cuts the +ve lead of them (the yellow and red). The red and black wires from the relay will now be threaded along that green path above and into the accessory plug.

The relay is wired in by soldering and I have heat shrinked the connectors for safety. I wrapped a cable tie around it and anchored that to the Left Hand Side anchor point for the wire loom over here.

The green arrows point to anchor points (where the loom was held) except for the top red arrow which shows where the loom (also red arrow) will get held by a small metal "tang" which fastens it up there under the seat hinge.

I expect that its becuse of that possible rubbing against metal that this part of the loom had the extra protective sheath. I've supported that with cable ties pre-wrapping it with electrical tape, so as to keep it covering the wires.


I've been operating the bike for a week now, and done a number of small trips in and out of town (5 km) where the bike heats up to operating temp and after shopping or other business I've come back and tested if it was still discharging. To do this I
  1. pull the "auxilary" fuse, 
  2. test that there is no current across that fuse (there will be about 10mA from the clock, and a bit more from the seat light)
  3. turn the ignition ON to engage the relay
  4. measure if there is current across that fuse
  5. measure battery voltage
So now instead of winding down the voltage to the point where the bike barely turns over, the voltage is now a good 12.8V when I come back to it, and the relay is preventing the discharging.

Of course you will know if the relay is not working (and blocking current all the time) because the AutoChokes will be "ON" (as on this design they are powered OFF) and the bike will run like a bucket of shit when its warm.

Job done :-)


nbnuno88 said...

Hi there, great article
I have exactly the same problem, I owner a Tmax 500 Carb,
Can you help me with this solution, can't understanf the picture, need to buy another relay?
What king of relay,

This actualy works? right now my tmax battery won't last a day.

obakesan said...

Yes, this actually works.
I would caution you that if you don't have a good competency with auto electrics DO NOT DO THIS.

The relay needed is just any SPDT relay will do. I bought one from an electronics store (and I'm an electronics technician by profession), it cost about $4

What exactly is causing you trouble with this? (so I don't write answers to what you aren't having problems with)

nbnuno88 said...

Thank you for the response my comment :) I appreciate that, don't worry, I have some knowledge about auto electrics, I will try to do this, and take some pictures on the way, can I send you some pictures, so you can see work?
Thank you in advance

obakesan said...

Hi, pictures are un needed but thanks.

If you have a specific question then ask it by all means.

You'll see that the lead length is short so you'll see why I put the cuts in where I did when you're in there.

I've just recently sold the bike and so I don't have it, but it went flawlessly from the time I did it till I sold it (like 3 weeks ago now). Still ran on the same battery :-)

Be sure to insulate everything carefully, use some heat shrink as well as electrical tape and be careful where you route the power supply leads for the relay so that they don't foul on anything and don't wear through and short out on anything conductive.

I picked the most compace 200mA relay I could that was also going to take the 2A that the autochokes will suck.

Best Wishes

obakesan said...

btw, the 200mA is the draw of the relay, it must be able to handle a few amps that the autochoke solenoids consume, I picked a 10 Amp relay

nbnuno88 said...

Hi Obakesan,
It's not easy to do this, I have to disassemble all the cable the get the one o feed the yellow and black wire, can use two relays instead of one?
Thanks in advance

obakesan said...

There is ZERO purpose to use two relays ... look at the circuit diagram ... you insert one relay in the circuit straight after the thermo switch. Yes some careful opening of the loom casing is needed, yes you will need to take masurements and observe the colour codes.

As I say, if you feel uncomfortable to do this then do not. What you are writing suggests to me that this is outside of your ability, so don't do it.

Just buy another battery or keep putting it on the charger