Topic: Having trouble with my '75 CB400F - Battery constantly discharging

[mkngt]

Hello all! I recently started riding and picked up a 1975 CB400F with 12k miles.

I bought it rode it for 2 days, which was completely fine. It had a lead sealed battery, which unfortunately died after a few rides. I decided to get a new battery (anti-gravity lithium battery), and also bought a new rectifier/regulator combo (https://4into1.com/regulator-rectifier-honda-cb350f-cb400f-cb500-cb550-cb750/) because I read that I should upgrade both parts if switching over to lithium. Things were working fine, until the bike would die WHILE riding, especially when driving downtown. Almost all occasions where the bike would die, I was unable to start it up again (kicking was impossible, and I got nothing out of the push start). After it happened multiple times, I began to notice that the neutral/oil light would be extremely dim minutes before it would die and not have enough juice to start again. Because I was stranded, I was told I could possibly jump the battery with a car (car was completely off when I jumped it), but it would die off even when I was revving. I realize this could've messed up battery doing so, but AFAIK lithium batteries are able to be discharged/recharged.

I figured that it might be the new regulator/rectifier piece I put in, and switched it back to the original stock pieces. I would then recharge the battery to full, only to have it still randomly die out after a few rides still. I'm trying to narrow down what could be the issue, and here are some observations I've made.

• Using a voltmeter, the bike does 'charge' the battery when revving. I would start at 12.5, rev the engine, and the meter would read 12.8+
• The battery charges fully and can hold a charge after sitting over a week
• When idling at 1200 rpm, the bike quickly discharges, approx. 5/100 V a second. Revving it past 2000 rpm, it charges and can go up to 13.5V (see video)
• Changing the idle to 3000 rpm seemed to have 'fixed' the issue, although this isn't the fix I am looking for
• 400F is a sick bike and I intend to ride it until we run out of gasoline

I was told that this could be a stator issue, but I wanted to see if anyone had any suggestions or tips to narrow down what could be wrong.

[robvangulik]

Why did you switch to a lithium battery?
As i read it, the bike had been working fine for over 40 years with the original setup.....

[mkngt]

Why did you switch to a lithium battery?
As i read it, the bike had been working fine for over 40 years with the original setup.....

The bike ran fine when I bought it, but died after a few days of riding (lead battery, died in same way as the lithium battery). I thought it was a bunk battery (since the seller said he hadn't rode it in awhile), which is why I switched over to a lithium battery. I do have access to a normal lead battery if you think that might be the issue.

[TwoTired]

What kind of electrical load mods have been made to the bike?

Be aware, the alternator make about a third of max output (150 watts) at normal idle.
Idle normally is a battery discharge mode as the stock bike draws nearly 120watts with lighting on.  Electrical "upgrades" can increase wattage draw regardless of alternator output.

Stock battery is a 12 ah capacity.  What is the AH of your new lithium? This will determine how long it will take to deplete under idle idle rpms.

Cheers,

[jakec]

He got the lithium battery because I have one and it was working fine for me (even though I said to just get a lead acid )

His bike is all stock, stock headlight, all stock electrics and wiring. The battery and reg/rec combo (now removed) were the only changes. The only difference between my set up and his is that I have an 8 cell battery and his is only 4. Does that contribute to a lower AH / quicker discharge under the same load?

Also, his battery hasn't been fully discharged, only to about 8.5 volts (that's when the all the lights on the bike go out).

[TwoTired]

Yes a 4 cell Li batt typically would have half the AH as an 8 cell..  But, capacities among brands can vary.  That is why you look at component specification.

The discharge curve of Li batteries have a very steep discharge curve when depleted.  They hold their voltage fairly flat until depleted, then fall to zero very quickly under load.  Remove the load and they will recover somewhat.  This is harmfull to this battery technology and no manufacturer that I know of will warrantee a lithium battery if abused in this way.

Lead acid is far more forgiving of this abuse.

Cheers,

[jakec]

They are both antigravity:

https://shop.antigravitybatteries.com/productline/starter-batteries/small-case/

My 8 Cell has been in use every day for about 6 months and never needed to be charged. I do know that it was discharged once or twice by the previous owner before I got my hands on it.

[TwoTired]

Has your "discharged" battery been tested to see if it ever got restored to full capacity?

How would you know if the battery is only working at 75% of new capacity?

There is a difference between damaged and destroyed.  Full dischrage to zero isn't guaranteed to destroy Li.  It can be harmful though, which is why such abuse is not covered by manufacturers.

Glad yours is still "working" for you.

FYI: a LiPFeO4 battery cell has no power when below 2v/ cell.  It is fully charged at 3.3 v/ cell.  There are charts available to determine percentage of charge remaining at voltages in between.

Cheers,

[jakec]

In the case of my battery, I have no idea how low it was ever discharged, probably as low as Mkngt's, to the point where it stops keeping the lights on (about 8.5V). There would be no reason it went lower than that because you stop trying to use it once the lights go out.

Mkngt's battery (4 cell) would have no power below 8.8V according to your benchmark, that makes sense.

My battery, when fully charged, usually shows within the 13.2-13.6 range. Mkngt's is only showing about 12.6.

[TwoTired]

Below is a discharge chart LiFePO4 lithium batteries.

The chart shows a pretty level discharge curve until depletion.
Note: they don't test them below 2V/cell.  This is because they quite often no longer perform properly when discharged farther than that.

Also note that if you discharge to 2v/cell, you can't humanly get to the switch fast enough to prevent the voltage from going lower in most cases.

Almost all manufacturer applications of Lithium battery technology in offered products has a smart circuit that prevents the battery from discharging too deeply, by interrupter or by current limiting automatically, without human intervention.

The SOHC4 has no such mechanism or device.  In fact, it doesn't even have a voltmeter to allow the operator to take preventive action in an attempt to save the battery from damage.

I use lithium tech batteries in my R/C gear, airplanes and cars, LiFePO4 and LIPO.   They have the battery protection devices/circuits to keep them viable.

Lithium tech is wonderful in the right application.  I just don't think the SOHC4 is the right application, as it doesn't have the proper charge controller to keep it in peak health, or any safety device to keep a lithium battery into long life.

I actually bought a Shorai battery for experimentation.  Starts the bike fine.  But, after learning about the technology, I took it out of the bike and use it for my RC gear instead.  I have a proper charger for it, and never let it deplete below safe levels.
 For the bikes, I use lead acid tech.  The SOHC4 vreg knows how to treat them properly.

Cheers,

[jakec]

So step #1 is buy a regular lead acid battery, charge it up, and run the same test? If the acid battery starts at 13.1 and we let the bike idle, what should the normal discharge rate be? Vs. the rate shown in the video.

[TwoTired]

Remember a battery is chemistry oriented device, that happens to have electrical side effects.  The chemical conversion inside either generates or accepts ions during the conversion.

A lead acid battery will actually surcharge when full, exhibiting higher than normal voltage.  After a rest of about two hours it should settle into a voltage reading of about 12.6 to 12.7 volts without any load placed upon it.  This is a full battery voltage all by its lonesome.
Loads discharge it, and the volts go lower depending on the duration and load magnitude.
A small lamp won't lower it much.  A starter motor load will make it dip much lower in voltage quickly.

To determine charging, you have to look at voltage trends.  Like the discharge volts, changing the amount of charge offered has an impact on Vrise.  Offer it an amp of charge it rises slowly.  Offer it 10 amps and the v should rise more quickly.

My metric is, if the known fully charged battery is showing more than 12.6 V, it isn't discharging.  But, it may only be accepting very small charge current.  Conversely, if it is measuring below 12.6 V it is in a discharge mode.  On a working bike, you can actually find what RPM the charging/discharging knee occurs by watching the voltage and manipulating the throttle.  But, the knee point will change with electrical load factors, such as lighting on or off due to the power limitations of the alternator.

Cheers,

[przjohn]

The 400F charging system is anemic. As has been stated the bike will discharge when idling, and get a known good battery in the bike. It sounds to me like the load is too great, meaning something has been changed like a light or ignition system causing a greater load on the charging system. It doesn't take much to overload these bikes.

[jakec]

We've looked it over and everything is stock, except for the right hand switch which we replaced with a replica. The headlight could be aftermarket but it's the typical sealed beam style.

Perhaps Mkngt can chime since I'm just the guy holding the volt meter..

[Bodi]

The charging system is sufficient when it's in good condition and the bike is used as expected. I would not recommend these bikes for a Shriners parade troupe where they would be idling around in circles all the time.
Several things happen that degrade the charging abilty. #1 is corrosion in the harness connectors, fuseholder, and switches: this causes a voltage drop through the harness. The alternator converts field coil current into output power. The field coil current is proportional to its supply voltage. Any voltage reduction at the field coil means a drop in alternator output. Cleaning and maybe tightening (where needed) the bullet connectors and other connectors in the harness can eliminate a lot of voltage drop. There is a set of bullet connections under the sprocket cover in the alternator wires: these are often in very bad shape from the constant high current and the environment they're in.
#2 is modifications. The power balance is pretty tight, with little headroom for extra load. The headlight should not be "upgraded" to a high wattage type... these can be sealed beams or with H4 lamps. Driving lights, heated grips, whatever... may result in poor charging even at highway RPMs.
#3 is riding habit: you want to keep RPMs up - for the health of the engine and for charging. Highway driving will always be at charging RPM - but for city riding and general local road cruising at 30-40MPH you don't ever use 6th gear, period, and rarely use 5th. Lugging the engine (defined as increasing throttle in gear without increasing speed) just carbons up the cylinders and plugs as well as probably causing battery discharge just from low RPMs. This engine like high RPMs, it isn't a cruiser V-twin happy chugging down the road. If you are riding at 30MPH in 6th, you're abusing the engine.

[scottly]

Is the bike started by kicking, or using the electric starter?

[evinrude7]

if you're cruising around town keep the revs high and don't use the starter.  kick it every time. 

[mkngt]

I am using the kickstarter, rarely ever touch the push start.

I do know to keep the RPM at around 6k, will do a more conscious effort to keep it high!

As far as I know, nearly all the electrical components are stock.

I'm going to get a lead battery and let you know the results.

I've posted some photos too of the rectifier/regulator, please let me know if something is supposed to be grounded or if something looks sketch!

https://imgur.com/a/PCxLZZ2

[jakec]

Mkngt rode to work today with his idle turned up to 3,000 

[jakec]

Mkngt rode to work today with his idle turned up to 3,000 

Akin to having an IV transfusion of blood for a paper cut on your thumb.

He also left his keys in the bike.. what's the analogy for that?

[TwoTired]

Why not tape a voltmeter to the bike where he can read it while riding?
Let the voltage inform whether the bike is charging or depleting.
Could be, 2000 rpm or even lower keeps the battery in shape.
Or, is a larger battery to buffer during the idle periods that distasteful?

Cheers,

[jakec]

It seems like the voltage stabilizes around 2,000 rpm. He is planning to buy a normal lead acid battery later today.

[Robbo]

Don’t cheap out on the lead acid battery.


Sent from my iPhone using Tapatalk

[mkngt]

Don’t cheap out on the lead acid battery.

Yeah I just bought one. I'm about to go on a week long trip, but I will keep you updated when I start testing when I get back. Thanks all

[spurlock]

IMHO there are two things missing in this thread: First, to evaluate charging system output stop looking at battery voltage readings and instead connect an ammeter in series with one of the battery leads so you get a real-time picture of charging current. Running battery voltage is the result of charging current so it is a lagging indicator.

Second, use a logical step by step diagnostic method rather than random parts changing or piecemeal testing. Mike Nixon's excellent web site has the most logical step by step method I have seen or used, link here:
https://www.motorcycleproject.com/text/SOHCcharging.html

-Bill