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Discussion Starter · #1 ·
Hey everyone, kinda new to the forums and I've been doing some reading.
I picked up this bike for really cheap about a year ago and I've been working on it a bit since. One issue that I've encountered is a brand new AGM T battery that I got for it a while back went bad within a month or so.
So I've been running through some steps to check the charging system and at 1500RPM im already getting 15v +/-.5 to the battery.
It seems kinda of high to me and was curious as to what I should be getting when running. Idle seems alright and holds at around 13v pretty steadily.
Should I rev it up a bit higher and see if the R/R doesn't limit it at 15? I just don't want to fry the battery.
The yellow plug has been replaced by spade connectors by the PO and I did some wire splicing and soldering some new waterproof plugs and a new ATC blade style in-line fuse. (Definitely not because I hooked a battery up backwards or anything...)
What would you guys reccomend testing to check if it's bad?
I tried doing the Ohm/Diode test on it but I don't get any reading from the yellow connectors. At the store I get .2-.3 ohms between all wires which is fine, correct?
I have the PDF manual, but I'm kinda lost.
Thanks ahead of time, all help is appreciated.
 

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The manual should give you all the tests and specifications. It’s an old bike, so it’s never surprising when things are a bit tired on it. Also, it’s a really good thing you never hooked that battery up backwards. That may not have helped matters if you had... 😉
 

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Shadow VT700c 1986, ST1300 08
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15V is what the manual says.
Have you test the battery for gravity?
Your current (the bike obviously) should be up to 1.4A when at 15V
Also check the resistance on the stator coil as below.
You will also should check that the charge starts at around 1,000 rpm and not much above that.
294165
 

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Discussion Starter · #4 ·
Ha, I'm sure that jolt would great for the system, if I had done it. 😅 I'll take a peep a bit closer when I can pull it up on my laptop, reading PDFs on my phone is rough.

Thank you Husoi, I will check the stator one more time. It was a little cold this morning when I check the resistance so I will see if it climbs to .3 when it warms up.
I've never checked gravity on a battery before so I'll look into it. The current battery is a new(as of yesterday) duralast AGM from autozone.
 

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Shadow VT700c 1986, ST1300 08
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If the battery is new you don't have to check it.
Gravity check is a fancy name to check the acid density. Being an AGM you can't check that.
The best way to know if the regulator is playing up is with the headlights.
Low beam should stay more or less stable when varying the rpm
on high beam it will become a bit more sensitive and would oscillate with rpm.
To add to the load of the high beams you can action the brake so it loads more the alternator.
at idle high beam you will see a kinda oscillating light, as long isn't too noticeable you will be fine.
 

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Discussion Starter · #6 ·
I
If the battery is new you don't have to check it.
Gravity check is a fancy name to check the acid density. Being an AGM you can't check that.
The best way to know if the regulator is playing up is with the headlights.
Low beam should stay more or less stable when varying the rpm
on high beam it will become a bit more sensitive and would oscillate with rpm.
To add to the load of the high beams you can action the brake so it loads more the alternator.
at idle high beam you will see a kinda oscillating light, as long isn't too noticeable you will be fine.
Ahh gotcha. Will give it a shot when I'm home. 👍
 

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How good is your meter? The cheap meter I used to carry was telling me I had 16v at idle, (While 1100 miles from home... ) It then told me I had 2.25v in my AA battery, So I trash-canned it.

And check the stator each yellow lead to the others and each to ground. Should have 0.3 ohms between leads, open to ground, Also check the meter leads to each other and subtract any reading there from the stator readings. Though if it's capable of putting out 15v DC, then I'd have to think the stator is good. Rectifier may have issues, rev it up, if it goes over 15, I'd replace the rectifier.

Roadstercycle.com has some good videos on checking stators and rectifiers. left side of page, then scroll down.
 
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Discussion Starter · #8 ·
How good is your meter? The cheap meter I used to carry was telling me I had 16v at idle, (While 1100 miles from home... ) It then told me I had 2.25v in my AA battery, So I trash-canned it.

And check the stator each yellow lead to the others and each to ground. Should have 0.3 ohms between leads, open to ground, Also check the meter leads to each other and subtract any reading there from the stator readings. Though if it's capable of putting out 15v DC, then I'd have to think the stator is good. Rectifier may have issues, rev it up, if it goes over 15, I'd replace the rectifier.

Roadstercycle.com has some good videos on checking stators and rectifiers. left side of page, then scroll down.
I'll rev it a bit higher, if It goes above 16v I'll probably replace it.
Also thank you, thats what I forgot to do. I didn't check between the yellow leads and ground.

Do you happen to know any decent R/R's to get? There seems to be quite a few different options. Some requiring slight modding for mounting and what not.
 

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Discussion Starter · #9 ·
Also my meter is pretty alright. I just trashed my other one as well because it stopped reading correct. 🤷‍♂️
 

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If it goes above 15 I'd replace it. (the newer LiFePo4 (Lithium-Iron phosphate) batteries don't want more than 14.8v DC. Tough call on rectifiers, I've used the Mosfet type FH020 and the Series type SH847, but they are much larger than stock and you might have trouble mounting them, Rock-steady 14.5v though... There are a lot of fakes out there now too. Most anything that fits should work. The standard 1100 rectifiers are larger than the 750 Ace one. Most all bikes in the last 20 years or more are a 3-phase Permanent Magnet system and self-contained. 3 wires from stator to rectifier and a positive and negative connection to the battery. My opinion is the larger ones have more capacity for dealing with heat build-up and may provide a more stable voltage. other side of that is the standard Honda one worked for decades. No reason to think a new one wouldn't work fine. Your call.
 
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Discussion Starter · #11 ·
Greatly appreciate the insight, I'll see what I can get ahold of and keep the thread updates.
Thank again o/
 

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Just remembered yours is an 84. Check your wiring schematic, iirc some of the earlier stuff had a 6th wire from the rectifier, used for various functions.
 
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My 1983 750 was starting to get up to 15 volts and a little above. I have a digital meter on my dash to keep an eye on the charge system. It had the original regulator. So I bought a cheap aftermarket one just to see what that would do. It stays down around 14.5 now. If the cheap reg goes bad I will buy a quality one.
Yes those early ones had a black wire from the ignition also that later ones don't have.
 
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I'm assuming the black wire is simply not used with a newer rectifier?
 

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Discussion Starter · #15 ·
I think I might be investing in a new regulator. With high beam and brake lights on im still seeing 15.1 at idle and 15.5 when revved up, but oddly enough it doesn't go past. I may go with a cheaper one and install a voltage readout and cross my fingers.

Maybe not too cheap, but probably not above $100, can't afford it right now. 🤷‍♂️
 

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I bought a cheapy like this and it works but had to make a different bracket because of the shape.
Or get the triangle one and it would fit right on the bolts.


 
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Discussion Starter · #17 ·
I bought a cheapy like this and it works but had to make a different bracket because of the shape.
Or get the triangle one and it would fit right on the bolts.


I actually wound up ordering that one, it should be here on the 7th. So I'm looking forward to it.

I can't imagine 15v at idle under load is right. So I'll install it this weekend and give everyone an update.

I know there's a ton of threads on this but sometimes talking it out really helps.
So, thank you all.
 

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If it goes above 15 I'd replace it. (the newer LiFePo4 (Lithium-Iron phosphate) batteries don't want more than 14.8v DC. Tough call on rectifiers, I've used the Mosfet type FH020 and the Series type SH847, but they are much larger than stock and you might have trouble mounting them, Rock-steady 14.5v though... There are a lot of fakes out there now too. Most anything that fits should work. The standard 1100 rectifiers are larger than the 750 Ace one. Most all bikes in the last 20 years or more are a 3-phase Permanent Magnet system and self-contained. 3 wires from stator to rectifier and a positive and negative connection to the battery. My opinion is the larger ones have more capacity for dealing with heat build-up and may provide a more stable voltage. other side of that is the standard Honda one worked for decades. No reason to think a new one wouldn't work fine. Your call.
It would not be the battery that would cause it to go over 15v, it would be Rec/Reg.
 

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I think I might be investing in a new regulator. With high beam and brake lights on im still seeing 15.1 at idle and 15.5 when revved up, but oddly enough it doesn't go past. I may go with a cheaper one and install a voltage readout and cross my fingers.

Maybe not too cheap, but probably not above $100, can't afford it right now. 🤷‍♂️
I own a 1986 VT700. Great bike. Its as fast as a modern 1100 because of its hp and the fact that its a 6 speed. Mine is in such good shape that I try to keep it original. One bad thing about that bike is that its really hard to find oem parts for.
 
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