Topic: real-world experience on amp-hour battery rating

[JoeP]

I'm getting ready to fit a battery to my cb550 project and would like to know peoples' experience on running a battery with a ~6-7 AH rating. I know the stock battery is 12 AH and a lot depends on the particular electrical setup. My setup will be electric start, stock headlight, LED turn signals and tail light, no running lights, stock coils. I've read the faqs, but does anyone with a similar setup find that a 6-7AH battery (with about 100 cca) works well in the real world? In my case, I'm not planning to do a lot of city driving. I'm thinking of this battery in particular: http://www.amazon.com/BikeMaster-TruGel-Battery-MG7Z-S/dp/B0041CC3H6.

[vames]

So it looks like you have a basically stock setup with the exception of LED blinkers and no running lights, you want to keep the electric start, and you want to do it all with half of stock battery capacity. I'm no expert, but the math doesn't add up.

[TwoTired]

Plan on frequent battery replacement (yearly, I'd guess at minimum).  But, it will probably "work" when first installed, and with the battery, engine, and oil warm.  Hope for an engine that starts quickly and doesn't pull a lot out of the battery when starting.  Using the Kick start whenever possible will help with battery life.

There aren't enough current draw numbers stated for your particular bike, to do an accurate projection.  Further, some CB550s have a headlight off/on switch and others don't.  No information about that either, or whether your "LEDs" have ballast resistors in them to mimic standard bulb loads.

The bike loads take away from the 5000 RPM max alternator output capability (150 watts), as well as the idle generation of about 50 Watts.  Normal Cb550s draw 120 watts whenever the key switch and lighting are on.


I can't tell what your "real world" is like.  But, I wouldn't want the small capacity battery you propose on my bike.  Then again, it ain't no cafe racer, either.

[JoeP]

So it looks like you have a basically stock setup with the exception of LED blinkers and no running lights, you want to keep the electric start, and you want to do it all with half of stock battery capacity. I'm no expert, but the math doesn't add up.

Math: http://forums.sohc4.net/index.php?topic=101689.msg1136959#msg1136959. Look at TwoTired's minimum lighting example. Say the system draws ~120W and you're at idle so your battery has to provide all (most) of the power. At 120W with 12V you draw 10A, which means that with a 6AH battery, you got about 36 minutes at idle. If I spend most of my time at 3000rpm or above, it looks like my alternator can provide close to everything I need (on paper). Hence, my question.

[JoeP]

Plan on frequent battery replacement (yearly, I'd guess at minimum).  But, it will probably "work" when first installed, and with the battery, engine, and oil warm.  Hope for an engine that starts quickly and doesn't pull a lot out of the battery when starting.  Using the Kick start whenever possible will help with battery life.

So the continual charge/deplete cycles will kill it over time even if it was on a tender in between rides?

[Jerry Rxman Griffin aka MuthaF'er]

IMO if it will turn the electric starter and your charging system is optimal and you keep the rpms up to where your system is outputing more than the load then go for it. Your battery is just a storage device and the charging system runs your bike but the battery needs to allow the current a path through it.

[TwoTired]

So the continual charge/deplete cycles will kill it over time even if it was on a tender in between rides?

Yes. 
Starting batteries are made differently than deep cycle batteries, mainly in the plate separator technology.
The electrolyte facilitates the movement of metal ions from one plate to the other.  Charging reverses the movement, but the metal ions don't find the same place they leapt from in the reverse direction.  Over many cycles, the plates develop holes, which reduce their current delivery capability though loss of plate area.
Alternately, some battery electrode plates are made porous to increase the surface area and recharging tends to fill in the pores, again reducing plate area exposed to the electrolyte.  This makes the battery weaker at peak current production over successive charge/recharge cycles.   

Larger batteries won't normally discharge as deeply, and this lengthens their useful life.

Remember, batteries don't store electrical energy directly.  They are chemical devices that make available or consume electrical energy in the process of internal chemical conversions.

[JoeP]

Ah, thanks for the explanation. I guess the idea is to make the drain a small portion of the reserve so everything is more reversible. I'll sacrifice form for function in this case and go with a larger battery.
 

[scottly]

Joe, the deal breaker in your case is keeping the electric start; the largest battery I've had on my kick-only 750 for the last 15+ years was 3 A/H.  

[Fritz]

At 120W with 12V you draw 10A, which means that with a 6AH battery, you got about 36 minutes at idle.

That would be in an ideal world. But the OP was asking for the "real world". So that would be more like 15 minutes (depending on temperature, age of battery, etc.). My rule of thumb is: real capacity = nominal capacity / 2

[dave500]

if the bike starts quickly and easy without cranking it for long and you ride country mostly itll more than likely be ok?

[TwoTired]

Joe, the deal breaker in your case is keeping the electric start; the largest battery I've had on my kick-only 750 for the last 15+ years was 3 A/H.

The 750 also has a 210 Watt alternator instead of the Cb550 150 Watt.   It matters.

[bikebodger]

as your building a special ,why not install a modern sealed hi output battery ,the battery on the current r1 or fireblade has loads of ah capacity & is quite slim.you could tuck it into a caferacer seat hump or similar.i always use modern batteries on my classics.half the size & twice the amps,plus no acid spilling & ruining paint or chrome.the standard battery was the best they could make in the 70s & battery technology has come on a bit
  i have just checked out your first post ,that battery will do the job .its the one i use just get a proper brand not that chinese one.buy one with a separate acid pack that you install & then sets in the battery ,you know its a fresh battery.some of the gel batteries have been stood years & are past it

[scottly]

Joe, the deal breaker in your case is keeping the electric start; the largest battery I've had on my kick-only 750 for the last 15+ years was 3 A/H.

The 750 also has a 210 Watt alternator instead of the Cb550 150 Watt.   It matters.

No, it does not matter. The maximum output of the charging system is irreverent to required battery capacity. If the system is always drawing more power than produced, the battery will discharge. A battery with a larger capacity will simply take longer to discharge and recharge.
The electric starter requires large current draws, requiring a higher capacity battery than a kick-only bike, where the battery only needs to supply a few amps of current for a few seconds before starting. 

[TwoTired]

Joe, the deal breaker in your case is keeping the electric start; the largest battery I've had on my kick-only 750 for the last 15+ years was 3 A/H.

The 750 also has a 210 Watt alternator instead of the Cb550 150 Watt.   It matters.

No, it does not matter. The maximum output of the charging system is irreverent to required battery capacity. If the system is always drawing more power than produced, the battery will discharge. A battery with a larger capacity will simply take longer to discharge and recharge.
The electric starter requires large current draws, requiring a higher capacity battery than a kick-only bike, where the battery only needs to supply a few amps of current for a few seconds before starting.

Assuming you meant irrelevant, which would make more sense.

But I must disagree.  The Cb750 and the Cb550 generally have the same current draw in both modes; lights on or lights off.  Both alternators make about 1/3 of max rating at idle, with some examples working better than others due to production and manufacturing variables.

1/3 of 210 is about 70 watts, vs 50 watts for the 550.  Meaning the 550 will always draw a battery down faster and work it more than a 750 would.
Cb550s with the lighting off still deplete the battery, while a Cb750 with the lights off does not, because more power is available from the alternator at low speed.  Smaller batteries will "fatigue" faster, particularly if they are of the "starting battery" class rather than the deep cycle types.

So, the charging system minimum output does matter.

[dave500]

i never have charging troubles,be sure all your connectors are clean,this is with a modern rectifier and separate electronic regulator,if your riding stop light to stop light youll drag your battery down.