is there an AGM battery for an st90?

Drew_P

New Member
my childhood st90 is in the process of being revived. It is mostly running, but I need a battery for it. The original was super dead after 20 years in a barn, so my enterprising uncle cut out the push connectors and put in a 6v battery for his deer feeder. And lo and behold, it worked. But, a year later, I've noticed that the battery is severely bulged and scary looking.

so it looks like the stock battery is something like this https://www.amazon.com/UBC41517-6N5-5-1D-POWR-SPORTS-BATT/dp/B001XVEM22

but is there a good AGM battery that will work instead? I found this https://www.amazon.com/Motobatt-MBT...N97D7SDCG03&psc=1&refRID=1R691ZPZ1N97D7SDCG03
and this https://www.amazon.com/Jiming-JM-6M...6v+6ah,automotive,173&sr=8-18#customerReviews
 

OLD CT

Well-Known Member
I am ok with the standard deer feeder batt. What you need to do with whatever batt you go with, as soon as you install it hook up a voltmeter to the battery running and rev it up a little and watch how many volts you are pushing. It sounds to me like your ''voltage regulator'' or also known as a rectifier took a dump and is not limiting the voltage and the battery is getting overloaded. No expensive/fancy batt will stop that.
If you see 8+ volts there is a problemo! Around 7.5 is fine. Test with lights off and on to note any differences.

Good luck!
 
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b52bombardier1

Well-Known Member
The lead acid battery also does a good portion of the voltage regulation. And a lead acid battery is better able to tolerate the high RPM, high voltage situations better than an AGM - it won't bulge out.

Rick
 

Drew_P

New Member
is this the voltage regulator? https://www.amazon.com/dp/B07CSHMH5...c=1&ref_=sspa_mw_detail_1&smid=A1EYXCZKZ0TGKP

once I reassemble the carb I'll try and get this thing started again and see what the voltage is doing. Should I be measuring across the battery terminals or some other place? I don't mind doing the deer feeder battery as long as it safely works. I do want to avoid the lead acid batteries if at all possible.

I pulled the tank and tried my best to de-rust it with nuts and vinegar. Seemed to work out ok. I installed an inline fuel filter as well. and of course I reassembled the petcock wrong and leaked fuel all over the garage. :( live and learn. Also, getting the tank back in was a true pain in the butt.
 

Drew_P

New Member
well, voltage is 6v right now. I couldn't get it started, so I cannot check that. I took apart the carb and installed an inline fuel filter, and I'm leaking gas from somewhere on the carb. I may just need to buy a new carb. this whole 50 year old dirt bike think is more work than I anticipated. And it seems like the more I work on it, the worse is gets.
 

OLD CT

Well-Known Member
Sounds like jumping the gun, shopping on Amazon. Test the regulator then pull out the regulator that is in the bike and match it up to what you are shopping for. I don't shop on amazon for bike parts. Buy from a reputable vendor and buy genuine parts if it is still available. If OEM is not available, than I totally get it. Don't be in a rush to buy junk... Also just because it says Honda doesn't mean it's worry free, especially a 50 year old bike. The good thing is, it is easy to work on. If you want worry free a new Monkey is right up your alley.

6V not running says nothing...
 

b52bombardier1

Well-Known Member
That Amazon part is only a voltage regulator in the most vague sense. A healthy six volt lead acid battery that is tied into the electrical system / accepts recharge current and the bike's lighting is what really regulates voltage here.

I'd be curious to know the internal electronic characteristics of that Amazon part such as its peak inverse voltage rating. Mouser Electronics and Digi-Key have these with a rock crushing 1000 volt PIV rating that can come in handy with a high engine RPM flip of the headlight switch. The electrical system on these bikes can see very short but very high voltage transients at high RPM when a big lamp is switched on or off - makes it tough on rectifier diodes.

Digi-Key bridge rectifier part #GBPC2504DI-ND

Manufactured by Diodes, Inc. as part # GBPC2504

http://digikey.com/scripts/DkSearch/dksus.dll?Detail?name=GBPC2504DI-ND

Typical 25 Amp Silicon Full-Wave Bridge Rectifier
Body has no electrical connection, all terminals are isolated.
Small bikes put out less than 10 Amps so the 25 Amp rating is overkill.
Such low Amps will barely run it warm. No heatsink needed. Bolt to frame.
This unit passes more Voltage to the battery than the stock rectifier.
This unit will withstand 400 Volts reversed and briefly, a 300 Amp surge.
As of today, these cost around four dollars plus shipping.

GBPC2504-E4/51GI-ND This is the recommended replacement for the above part
number.



Rick
 
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