application notes

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Here at Racing Batteries we build high performance lightweight lithium batteries. We don’t have the skills or experience to build winning race bikes or supercars, and we wouldn’t presume to tell anyone else how to. But we have picked up a few things about how lithium batteries behave in certain applications and we thought we’d share some of them here – poor starting performance is bad enough, but missed practice is worse!


Quiescent Current Drain

Check how much current the vehicle is drawing when everything is switched off. Ideally this should be zero; if it’s not, should it be? If it’s not zero, ideally disconnect the battery when it’s not in use, or consider fitting an isolator switch. If there is quiescent current drain, the battery is losing starting performance all the time the battery is not on charge. Left to its own devices, this quiescent drain will eventually take the battery below 8V, permanently damaging it. 

Ground Running

When the vehicle is switched on before engine start, the battery is powering all the electrics, and the battery voltage is falling. Find out what the ground running current drain is – it may be more than you think. With a big lead battery you have lots of excess capacity, so this drain won’t affect starting performance – with a low capacity lithium battery, even a few minutes of ground running could take the edge off starting capability. If you’re downloading data, checking electrical systems etc, consider keeping the battery connected to a charger right up to starting. 

Cold starting

If you’re running the lightest unit possible, then a jump start from a big lead battery when the motor is stone cold is good practice, and reduces stress on the lithium unit. But make sure you use heavy duty cable for the jump leads and connection to the loom - at least as thick as starter cable.

Tickover

You’ve started the motor, so the battery is charging, right? Maybe not. If the battery voltage is higher than the alternator output voltage, then the battery is discharging. If your battery was fully charged (and it should be), then it will be around 13.6V, and your alternator may not be putting this out until much higher in the rev range than tickover (especially with a kit/lightweight alternator). So, once again the battery is discharging – and starting capacity is falling too – could be embarrassing if you have to restart on the grid! So, it might be a good idea to have a look at generator output and loom voltage at tickover/low revs – is loom voltage rising or falling? The only way to make up for the battery not charging is to run a bigger one, so that it can still provide enough starting current when not fully charged.

Alternator/Charging Voltage

The lead batteries you’re probably familiar are fully charged at 12.8V. A lithium battery is nearly flat at 12.8, and its starting capability is seriously reduced. So for the vehicle to charge the battery when it’s running, it needs 2 things: 13.6V or more loom voltage most of the time and time for the battery to charge. If you’re only hitting 13.6 for some of the lap, the battery won’t be charged when you come back in – do you have to start in parc ferme? We have developed some kit generators for modern sportsbikes that will give you the voltage you need - contact us for more details. The only way to make up for the battery not charging is to run a bigger one, so that it can still provide enough starting current when not fully charged.

Start Map Ignition Advance

You might need plenty of ignition advance at very high RPM, but you don't need so much when you're starting - you may find that reducing the advance in the start map makes starting considerably easier, and may allow you to run a lighter battery.

Installation

  • Keep an eye on heat and vibration – ideally keep the battery away from both.
  • Don't mount the battery directly to the frame or engine - a bit of vibration isolation is a good thing.
  • Put the battery wherever you like, but the further you put it from the starter motor, the thicker the cable you’ll need – and the thicker the better! Ideally, get the battery as close to the starter motor as possible, using the shortest, fattest cable you can.
  • Choose your battery terminal bolts carefully. Steel is an insulator (well, nearly). Brass conducts current 68% better than steel, and aluminium is 4 times better. Lead is only half as good as steel.

 

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