What's my battery voltage - 36v or 48v?

[badnewswade]

I've decided to replace my lead-acid battery with dry cells rather than mess about with over-volting, but I'm not sure as to the voltage of the Sakura battery.

I was wondering, has anyone ever taken a voltmeter to their Sakura or other sub-moped battery? Because mine reads as 48v despite Sakura's claims of 36v - I suppose 12volts for the lights and indicators and 36v for the motor and controller?

But then my friend pointed out that this could be due to an on-load effect, i.e, 12 volt batts apparently show up as 14.4 volts if there's no load on them, so 14.4 x 43.2, which is close to 48... What's going on here? I need to know how many 10 amp-hour D-cells to order for a NiMH battery pack...

http://batteryjunction.com/dnireba.html

(apparently AAs overheat and are rubbish)

I don't know how much longer this sale is on for, but I can get the cells for about £160 - £170 inc p&p- pretty good huh?

[MalcolmB]

Not trying to be clever, but I'd really recommend you read around and get a better understanding of the basics before you make any more decisions:

Here are a couple of sites where you can find no end of useful and relevant information. I'd suggest you browse for a few weeks before jumping in at the deep end.
http://www.visforvoltage.org
http://www.endless-sphere.com

[badnewswade]

Is there any reason I couldn't run my bike off NiMHs? As long as I made sure to match the voltage and amperage?

I'm sorry if I seem pushy or anything, it's just that I need the info fast as the batts are a sale item- and depending on what the answer is and if I buy them, I could either end up with a white elephant, a missed opportunity or a fantastic DIY deal (new lead-acids for this bike are £140).

At the Sakura dealership today they were less than helpful, had to talk to someone on the phone and they were saying that the lithium version of the bike was a completely different machine and converting to a different chemistry would require a complete rewiring so I'd have to just buy a brand new bike (£800!) - but I don't exactly trust this company, when the bike first came out in '04. apparently replacement lead-acids were about £70!

BTW, took another voltmeter reading. Definitely seems to be 48v there.

[aminorjourney]

Can you give us your bike and model number? I would agree with Malcolm though - do make sure you read things through on paper before jumping in!

I have an S200. It looks like this:



The only thing I can suggest is that
1) You're connecting the voltmeter to the batteries while they're still connected to the charger, or that your voltmeter is up the creek!
2) Someone has beaten you to it and modified it.
3) They've changed the spec and things are a different voltage to earlier models.

It is quite possible that your charger is over-charging the batteries to 16V per battery at the end of the charging cycle, which is really too high for the batteries you have in a standard Sakura machine.

Over-charging to 16V per battery would give you that reading of 48V but that would probably be shortly after you pulled the charger out. You should ideally wait for half an hour or more before taking a voltage reading to let the battery voltage settle.

I'm afraid I've never heard of this on load effect. I'm no battery expert but in my experiences I've never come across such a thing.

I know that it is tempting to try and upgrade the battery technology but I would think twice before doing it. Replacing your existing batteries like for like, (or for larger AH ones) is not a problem. It's straight forward and very easy to accomplish. Adding an additional 6 V to the lead acid pack then takes you into the realms of either independently charging the 6V pack or buying a new charger (and 42V chargers are uncommon).

Adding a new battery chemistry requires you to build or buy a new charger and in the case of NiMH and LiIon, LiPo etc, a battery management system.

If this is your first foray into electric vehicles keep it simple. You will make mistakes (everyone does), and it's much nicer to learn that you've broken a set of cheap lead acid batteries than it is to have blown either NiMH or lithiums up. I got through two sets of lead batteries before I converted my car to Lithium and the rewiring was a mammoth task.

You can see just how much of a mammoth task it was here: http://flickr.com/photos/aminorjourney/ ... 628045492/

The final thing I would suggest is that if you're not already a member you [url="http://www.batteryvehiclesociety.org.uk/wordpress/?page_id=124"]join the BVS.[/url] and come on John Lilly's fantastic course about electric vehicle building on the weekend of 19th-21st October. It's held at John's farm in Wales and participants can camp out in his garden. For more information call John on 01874 730320. It would give you a lot of knowledge and helpful advice for just £20 for the weekend. The weekend will focus on electric bicycles as well as basic electric cars and you will end up with a working Sakura Plus (if I can coin that term) quicker than you may think.

Nikki.

[badnewswade]

Woah! That's some mission!

Testing... yup! Still 48v! And you've definitely tested yours and found it's 36?

hmmm....

Well, I have a different model of the s200, mine has bicycle spokes - as seen here:

http://www.austinev.org/evalbum/1370

Serial number is: S200406006

I'd guess from that that the bike was manufactured in 2004 - what dates / numbers do you have?

The thing about information on these things is that it's incredibly hard to get - Sakura are rather secretive and seem to publish no technical manuals, in fact they won't even let their dealers service the bikes!

Wish I could go on that course, but am broke. I can see what you mean about needing a battery management system - the only alternative I can imagine is to install a temperature sensor(s) and CPU fans for cooling.

Would still be a hassle, esp in traffic, and as someone else said, performance might well decrease due to internal resistance and so forth.

Maybe I should try overamping?

As for the possibility that it has already been "overclocked" - It's performance just isn't that good. You sometimes have to pedal to get away from the lights safely, and you usually have to pedal up hills. I haven't done a full on range test though - waiting for speedo to be delivered!

How much does your battery weigh? Here are some photos of battery and charger... are they the same as yours?





Interestingly there is no Sakura branding on either. (or any other branding info for that matter) The charger has no voltage info - just a serial number:
G4M20211-2347-E-16

I did around 12-14 miles yesterday (thanks Google Maps!) and took five hours to charge up. That doesn't quite seem to fit with Sakura's quoted 15-20 mile range and 8-hour charge time from flat, but it's still within a margin of error... isn't it?

Have I been landed with a non-OEM charger and / or modded battery?

[badnewswade]

PS - Is it safe to test the charger with a voltmeter? And should I oil the hub motor - it's a bit noisy, also I've tested voltage there and it runs that at 48V as well!

[aminorjourney]

Are you testing with more than one Voltmeter?

I still don't think that looks like a 48 V pack. It looks like the standard Sakura 36V pack to me - although I may be wrong. The charger certainly looks like the standard 36V variety.

Oh, and yes, the lights. They ARE 36V. A 12V lightbulb would glow rather nicely for a few milliseconds and then go bang.

[badnewswade]

That's a relief - will check with another voltmeter. Should the hub be oiled? Thinking of going back to the idea of overamping now...

[aminorjourney]

The hub is a sealed unit. Of course, you need to oil the chain and freewheel.

I understand you want a faster steed, but you may be better off getting a cheap second-hand bike and building a system from scratch. It would certainly attract less attention from the local constabulary as the Sakura looks very much like a moped.

[badnewswade]

Heh, yeah, there is that.

The lights were running off a 12v battery when I got the machine... seemed to work ok too until I started messing with the system.