GS500F Restomod Street Tracker

[SK Racing]

As some of you may have noticed, I've been endorsing the use of newer battery chemistries in motorcycles. To be more specific: LiFePO4 batteries. I don't advocate using any other type, like LiPo, Li-ion, or whatever. But LiFePO4, or LiFe batteries in short, tick all the boxes for small size, long life, zero maintenance, etc. There are some caveats, however. They don't like very cold temperatures, and balancing the cells is usually a necessity, whether that be with a BMS, active balancer or a charging balancer. I also wholeheartedly agree that one shouldn't fix something if it aint broke. So, if your bike's battery is working fine, don't change it out just for the sake of change.

In my case, with my project GS500 where I chopped off the sub-frame and built a new tubular "café racer" type sub-frame, space was scarce and the bulky lead-acid battery had to go. Fitting a much smaller LiFePO4 battery was the answer as it fits right inside the custom seat, under the seat pan. Obviously, I first made sure that the new battery was working OK by testing it for three months before putting saw to metal. It worked flawlessly, but I did realize that with such a small capacity battery (3.8Ah vs 10Ah stock), I would have to be more careful to not abuse it. That is typical of custom projects, I guess. There are often compromises.

I've shown this before, but here it is again... The size comparison of the stock and the new LiFe battery I'm using.


FEEDBACK
OK, here is my feedback on the use of a LiFePO4 battery in a GS500. (Please keep in mind that it is a DIY battery that I built from individual, soldered together cells)

When the cells were new, the one cell charged to a higher voltage. Not by much, about 0.7V, but I was concerned. A BMS with active balancing cured that phenomenon. The LiFe battery + BMS worked well for a number of months. But an engine oil change that coincided with winter temperatures introduced a problem. It turns out the 100A BMS is too sensitive and cuts out when trying to start on cold mornings due to the engine being heavier to turn from the cold new oil (10W40). The solution was to remove the BMS and now all is well. It starts easily without a hint of strain on the battery.

Is it safe to use this battery without a BMS? I would normally advise against it, but after carefully observing the cell voltages, I'm confident that the cells are now staying balanced, even without the BMS. So why is the same battery behaving different now? My guess is after working with a BMS connected for a few months, it seems that the cells got conditioned or maybe just properly balanced. I have a neat little device that draws a bar graph of the 4 individual cell voltages in real time. So I can check the condition of the cells while starting and also when the engine is running and therefore charging the battery. All 4 cells now hold the same voltage under heavy discharging (starting) and charging conditions – and without a BMS of any kind! The BMS that I've been using is rated for 100A and 150A burst, which seems too low for a 500cc engine when it's very cold. The 3800mAh (3.8Ah) LiFePO4 battery o.t.o.h. seems completely happy to deliver the amps - or cranking amps as they call it in the battery industry. I may add an active balancer later, just for peace of mind, but the battery seems to be happy on its own now.

I know most people are usually reluctant to try new stuff, but if you have been thinking about getting a LiFePO4 battery, hopefully this information will be helpful. I can't guarantee that you won't have problems, but if you size the battery right, I think your chances of success are very good. I know that commercial LiFe batteries made for starting vehicles have a BMS built-in. Therefore all you have to get right is the correct size for your vehicle. For normal usage in a GS500, I would suggest about 5Ah or slightly bigger as a sensible size. Unfortunately, some manufacturers only specify the cold cranking amps (CCA) and not the capacity. I can't help you there. Try to verify the cell capacity before you buy. CCA can be very misleading. Cell capacity is a more accurate indication of the ability to start an engine, if you have a benchmark to go by. Now you do. 

Last thoughts
I mentioned earlier that there are some caveats, although this one is not specific to LiFe batteries:
If you elect to use a battery of lower capacity than stock (10Ah), then the engine and carbs had better be in good nick. It should start easily. Smaller capacity batteries don't have the grunt to keep on cranking the motor while you try to start it. Do all starting troubleshooting with a stock battery first.

I'm thinking of getting one of these: Active Equalizing Balancer for 4S LiFePO4. Available on eBay and Aliexpress.

[cbrfxr67]

Really interesting and thanks for sharing!  I wish I knew more about electronics.  The size of the battery seems good reason for me to learn!

[SK Racing]

You're very welcome CB. I'd be happy to answer any questions.

[The Buddha]

That last sentence - if you're trying to start the thing with a weak battery the engine and carbs should be in good nick, That's true. I used to tune the carbs to start on a near dead battery.
Cool.
Buddha.

[SK Racing]

The latest gadget added to my bike is an automatic headlight switch. It will help with starting on cold winter mornings, because the headlight now stays off until the engine is running.

For those who didn't follow the development of the headlight switch, it was discussed in this thread: gstwins.com/gsboard/index.php?topic=73729

[SK Racing]

Update after riding the bike for seven months:

The LiFePO4 battery has been working flawlessly. I chucked the BMS after experiencing starting problems in very cold weather and pinpointed the problem to be the BMS, rather than the battery. So I'm now using the LiFePO4 battery straight - no BMS, but I did verify that all four cells stay balanced. I couldn't be happier with this tiny battery. It's always ready to start the engine, even after weeks of non-riding.

I did notice a small problem with what I think is weak fuel flow. Running WOT up a long hill results in slight loss of power after a while. So I have to look at the fuel filter, petcocks and fuel lines I suppose. During normal town riding it is not noticeable. Any ideas?

[SK Racing]

I couldn't help snapping this pic...

[cbrfxr67]

sweeeet

[cbrfxr67]

Jumped over here from the gs400 notcafe racer thread.  Speaking of batteries, I stuck a lithium pak in my bike a few months ago and seems like it's working a ok.  It was from a jump box, specifically a schumacher dsr128. It's about the size of a giant snickers bar.  Not really making a point here, only wondering what you think about that as you are well informed in batteries!

[SK Racing]

Sounds good. I checked and the Schumacher DSR128 uses two Lithium Iron Phosphate batteries, same chemistry as I'm using. It should last many years. So, well done! 

Does the pack give any indication of the capacity? Mine is 3.8Ah, but I won't recommend going smaller.

I also want to mention that even after the bike has been standing a month with no charging in between, it starts with the first crank. These batteries don't self discharge like lead acid do.

[cbrfxr67]

I believe it is 3.8.  It had a spec on it.  Thanks for the reply; figured you would know more than I do about it!  For me, I wonder why this hasn't caught on more?  I made another pak and stuck it in my buddies Vulcan and it's doing great.
On my wee bike I hacked a Milwaukee 12v charger and started using M12 batteries.  I barely finished a zs190 swap and it cranks it over easily.  I can't see going back to a traditional big battery unless I had to,....

[The Buddha]

You guys are running a 3.8 amp battery in place of the stock 10 ? Typically what counts though is the CCA discharge capacity, which can be 10-15X the rated amps. So a 10 amp battery would produce 100-150 CCA.
Do these batteries have a higher CCA than their 3.8 Ah would indicate (38 to ~55).
Also the rate is related to how much it will accept at near full charge. So a 10 ah battery will discharge 100-150 CCA and accept ~10 amps as it gets close to full charge. If the 3.8 only accepts 3.8 ah - you're likely sending a lot of wastage to the R/R likely shortening its life.
Ofcourse that is assuming the alternator is running at anywhere close to 100%, which likely is a stretch.
Cool.
Buddha.

[SK Racing]

You guys are running a 3.8 amp battery in place of the stock 10 ? Typically what counts though is the CCA discharge capacity, which can be 10-15X the rated amps. So a 10 amp battery would produce 100-150 CCA.
Do these batteries have a higher CCA than their 3.8 Ah would indicate (38 to ~55).

That's for LA (lead acid) batteries. Lithium is very different. These 3.8 Lithium packs deliver enough amps to easily crank the 500cc engine - and fast!

Also the rate is related to how much it will accept at near full charge. So a 10 ah battery will discharge 100-150 CCA and accept ~10 amps as it gets close to full charge. If the 3.8 only accepts 3.8 ah - you're likely sending a lot of wastage to the R/R likely shortening its life.
Ofcourse that is assuming the alternator is running at anywhere close to 100%, which likely is a stretch.

It's a common misconception that amps get "pushed". In reality, as the battery nears full charge, the charging amps diminish until it's basically zero. The losses in the R/R is related to the square of the amps, which of course is just about nil. So, the R/R is no worse off than with the stock battery and I'd imagine it's actually happier with a Lithium battery.

[SK Racing]

For me, I wonder why this hasn't caught on more?

Probably because people don't understand Lithium batteries and are scared of it. 

People are generally hesitant to try new things, even if they are aware of the benefits. Lithium has a 10+ year life expectancy. That means I'll  probably never need a new battery for my bike again.

[The Buddha]

Oh I am reading about CCA's and the AH rating. CCA's are bursts which I knew.
The AH is how many amps it can produce over an hour.
I thought the AH rating was the battery's charge rate close to full charge. Because I also knew when fully discharged it will take all the amps you can dump into it - its like an empty bucket. Or has near 0 internal resistance. Ofcourse near full charge it has high internal resistance and probably will rise rapidly to infinity at full charge.
Cool.
Buddha.

[larsensp]

Have any designs to share of the subframe? Wondering if you followed the shape of the tank coming off the frame, or brought it back in a straight line.

[Roofaloof]

Wow! Really cool build and amazing execution! Your bike looks amazing

[SK Racing]

Hey Guys and Gals

I haven't been on this forum for a long time, so I thought I'll post something again.

I'm still riding my project bike and lately I have been riding with my daughter. Sharon is 35 and she bought a Royal Enfield Classic 500 in January 2023.