Regulator Modification

Hello, I'm new to this site and hoping for some advice re. voltage regulation on a motorcycle alternator. I'll keep this as concise as possible but there is quite a lot of info to share...
The bike is a 1987 Yamaha FZ750, heavily modified for race use, and the alternator is a Nippon Denso ND3 (photo attached); I think it was made as a special for Yamaha. It is 3 phase and has field coils rather than fixed magnets. The regulator/rectifier (photos attached) is bolted to the end of the alternator and designed to supply charging current at 14.8V - 15.3V, which it does.
My problem is that for weight and space reasons I want to use a LiPo battery (photo attached) which will tolerate an absolute maximum charging voltage of 14.8V. In use the battery is less than 2" from the rider's primary reproductive organs so I'm keen to get this right...
It looks to me as if the rectification is being done on the coil winding side and the regulation on the brush side (photo)? Unless there are components in the resin casting (unlikely) I'm assuming that the whole regulator circuit is contained in the round can mounted on the brush side.
So... Is there a package similar to the OE one which will drop the charging voltage by 0.5V, or a little more? the battery drain is tiny so the charging rate doesn't need to be optimal. If there's nothing available 'off the shelf' could someone suggest a circuit I could build to achieve the required charging voltage.
Thanks for reading.

Welcome to ETO!
You can't safely just swap a lithium battery for a lead-acid one. Lithium batteries are dangerous if not charged properly and the cells making up the battery need monitoring individually to ensure they don't get over-charged. Special ICs for controlling the charging profile are available. Check out Battery University.

Hello Alec and thanks for your response, I'll check out your link.
The lithium battery is a LiFePO4 type like this one:
and is designed to replace a lead acid type.
One thing puzzles me - the round can where I thought the regulation might be happening has no heat sink attached to it at all. The other side, which has three conductors coming from the alternator windings and the output to battery +ve is potted, and has a substantial alloy plate epoxied to it. The alloy plate bolts directly to the alternator casing so must be acting as a heat sink - would heat be generated in the rectifier, or have I got it wrong and the regulator circuitry is buried in this potting?
Gavin

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Your alternator looks to work on the same principle as a typical car / truck alternator.

If that's the case, the rotor is an electromagnet with its strength controlled by the regulator & power fed to it by the carbon brush/brushes.

The power coils are in the stator.
The output from those is rectified and the voltage compared to a set target by the regulator, which adjusts the rotor field to try and hold it constant.

This shows an example of a similar Yamaha setup, with the schematic for a simple adjustable regulator:
**broken link removed**

"R1" is that circuit is often actually the ignition warning light or charge light, when a filament lamp is used for that.

A couple of other more generic examples:

Thanks rjenkinsgb that looks like exactly what I was after.
Your alternator looks to work on the same principle as a typical car / truck alternator - Yes.
I also found this earlier - looks suitable?
Gavin

Does you alternator meet the requirements at the bottom of your link?

- Charge current recommended 1.5 A


- maximum charging current for quick charge 15 A

The alternator spec says 25A at 5000rpm; it rises from about 3A at tickover to nearly 30A before the rev limiter kicks in. Is that a problem? I had assumed the battery would only draw the current it required. If not, those numbers look a bit scary...

FZ750Horse said:

The alternator spec says 25A at 5000rpm; it rises from about 3A at tickover to nearly 30A before the rev limiter kicks in. Is that a problem? I had assumed the battery would only draw the current it required. If not, those numbers look a bit scary...

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That's why I went to your link. Putting in ~30Amps when the battery is rated at 1.5 Amp charge is a big problem, or it would be for me. Your going to be putting close to twice the rated quick temporary charge in a constant manner.

Is this really a race bike or is it a street bike that looks like one? The reason I ask is the old sprint cars from back in the day didn't have a generator or alternator, they put a fresh fully charged battery in for each heat and replaced it for the next heat.

Is this really a race bike or is it a street bike that looks like one? The reason I ask is the old sprint cars from back in the day didn't have a generator or alternator, they put a fresh fully charged battery in for each heat and replaced it for the next heat.

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That's what started the whole project off. I raced the thing with Bemsee and it was running total loss with alternating lithium batteries, which was ideal for four races and two practise sessions over a weekend (the reg/rec in my original post came from a knackered alternator that I cut the end off to make a blanking plate). I am now into my 7th decade and definitely retired from racing but kept the bike and do a few track days on it. In this scenario the weight saving is not worth the faff, especially if the charging has to be done from a genny which is also trying to run tyre warmers and a kettle, so I put an alternator back on. I monitored the charging voltage, decided it was too high and changed the lithium batteries for a lead acid battery which is now at the end of its useful life. I have two perfectly good LiFePo4 batteries doing nothing so was looking for a way to use them but it's starting to look like more trouble than it's worth. I'll probably buy another lead acid battery and use the lithiums as doorstops .

Come to that, they're not even heavy enough for door stops

I'm just guessing here but back in the day, here in the States a common thing to do with Triumph's and other Brit bikes was a "Battery Eliminator". Basically a big capacitor that took the place of the battery, so you could still run lights to be street legal. I don't know if they still make them or if it would work for your situation if they do. A capacitor would be even lighter.

shortbus= said:

I'm just guessing here but back in the day, here in the States a common thing to do with Triumph's and other Brit bikes was a "Battery Eliminator". Basically a big capacitor that took the place of the battery, so you could still run lights to be street legal. I don't know if they still make them or if it would work for your situation if they do. A capacitor would be even lighter.

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I'm presuming that was for the very old Triumphs, that had a big zener diode on a heatsink mounted between the fork legs?.

They were a crude non-regulated alternator, just the coils, a permanent magnet spinning inside them, and a rectifier to feed the battery. The 'regulation' was simply the zener diode, directly across the battery, conducting if the voltage got too high and dissipating the excess power as heat

FZ750Horse said:

That's what started the whole project off. I raced the thing with Bemsee and it was running total loss with alternating lithium batteries, which was ideal for four races and two practise sessions over a weekend (the reg/rec in my original post came from a knackered alternator that I cut the end off to make a blanking plate). I am now into my 7th decade and definitely retired from racing but kept the bike and do a few track days on it. In this scenario the weight saving is not worth the faff, especially if the charging has to be done from a genny which is also trying to run tyre warmers and a kettle, so I put an alternator back on. I monitored the charging voltage, decided it was too high and changed the lithium batteries for a lead acid battery which is now at the end of its useful life. I have two perfectly good LiFePo4 batteries doing nothing so was looking for a way to use them but it's starting to look like more trouble than it's worth. I'll probably buy another lead acid battery and use the lithiums as doorstops .

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Probably as well, the entire system is designed for lead acid, and despite modern science it's still the battery of choice for cars and motorbikes.

FZ750Horse said:

I'll probably buy another lead acid battery

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If you want to save weight and don't need the battery for starting (most guys here use powered starter rollers) Just get a much smaller lead acid battery, you don't need to use the one made for the bike.

Nigel Goodwin said:

I'm presuming that was for the very old Triumphs, that had a big zener diode on a heatsink mounted between the fork legs?.

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That's the kind. When we made choppers out of them the eliminator was smaller and "cooler" than a battery box.