Solar Battery Tender - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 12 (permalink) Old 01-06-2009, 01:44 AM Thread Starter
 
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Solar Battery Tender

A lot of my daily (or maybe weekly) commuting is done just around campus for now more than a couple miles at a time. This clearly isn't enough to recharge my battery from the strain of starting my bike so I was looking at a battery tender. I have one that plugs into the wall but I am not able to park anywhere near an electrical outlet, even with a 1000 foot extension cord. So I was looking around at some solar chargers to hook up to my bike when I am parked in class or during the day to keep my battery up. My question though, is that my plug-in tender is rated at 1.5 amps, which seems to be good for our small batteries. The solar one I'm working at, however, is rated for 1.8 WATTS at 15v, which comes out to around 125 mA. I know I did the math correctly but am I reading it's specifications right? Would 125 mA take years to charge versus a 1.5 A charger plugged into the wall?

Thanks!
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post #2 of 12 (permalink) Old 01-06-2009, 02:34 AM
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Originally Posted by drguitarum2005 View Post
A lot of my daily (or maybe weekly) commuting is done just around campus for now more than a couple miles at a time. This clearly isn't enough to recharge my battery from the strain of starting my bike so I was looking at a battery tender. I have one that plugs into the wall but I am not able to park anywhere near an electrical outlet, even with a 1000 foot extension cord. So I was looking around at some solar chargers to hook up to my bike when I am parked in class or during the day to keep my battery up. My question though, is that my plug-in tender is rated at 1.5 amps, which seems to be good for our small batteries. The solar one I'm working at, however, is rated for 1.8 WATTS at 15v, which comes out to around 125 mA. I know I did the math correctly but am I reading it's specifications right? Would 125 mA take years to charge versus a 1.5 A charger plugged into the wall?

Thanks!

I believe that 125 mA = 0.125 A but not 100% positive. You might have better luck wiring a couple of lemmons to the battery. LOL


85 VN700 "Old Yella"

REBUILT ENGINE
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VANCE & HINES CRUZERS
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ORIGINAL STATOR & R/R 14.5v
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Last edited by lance328; 01-06-2009 at 05:05 AM.
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post #3 of 12 (permalink) Old 01-06-2009, 06:39 AM
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I believe that 125 mA = 0.125 A but not 100% positive. You might have better luck wiring a couple of lemmons to the battery. LOL
.125A is what I get.
While charging at lower amps for longer periods is a good thing, yeah.... that might take awhile.

IMO, your best bet is to plug it in to your tender when you get home or.... take the long way around the campus.


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post #4 of 12 (permalink) Old 01-06-2009, 08:37 AM
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Some hypothetical calculation, just for the fun of it.

Assumptions:
Lead acid battery self discharge is less than 10% per month, but let's assume it is 10%.
Lead acid battery efficiency is 75% or more, but let's assume 75%.
125mA from the solar cell charger probably is in optimal conditions, so let's assume that it delivers 100mA (0.1A).

Our bikes have (originally) a 14Ah battery, that means 0.047Ah self discharge per day. Just to maintain the charge you need to put in 0.062Ah daily. The 100mA charge current compensates the self discharge in 0.62h (about 37 minutes).

More assumptions:
The starter motor takes 80A (0.8kW to 1kW motor).

For every second you press the starter button, 0.022Ah of the battery capacity is used. To replace this, the charger must be on for 0.22h (about 13 minutes). The total charge time to compensate the starting is easily calculated: Start button pressed time in seconds * 13 minutes.

With the headlight on and the engine idling, is the battery charged or discharged I don't know, but I have a feeling that you don't need to ride for long to have a positive balance there.

So dare I make the final conclusion: On sunny days the 100mA solar charger may well be enough to start the bike several times a day for a short ride.
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post #5 of 12 (permalink) Old 01-06-2009, 08:44 AM
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For every second you press the starter button, 0.022Ah of the battery capacity is used. To replace this, the charger must be on for 0.22h (about 13 minutes). The total charge time to compensate the starting is easily calculated: Start button pressed time in seconds * 13 minutes.
HA! Forgot the 75% efficiency here! 0.029Ah is needed and the time is about 18 minutes.
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post #6 of 12 (permalink) Old 01-06-2009, 09:03 AM
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Quote:
Originally Posted by pappa View Post
Some hypothetical calculation, just for the fun of it.

Assumptions:
Lead acid battery self discharge is less than 10% per month, but let's assume it is 10%.
Lead acid battery efficiency is 75% or more, but let's assume 75%.
125mA from the solar cell charger probably is in optimal conditions, so let's assume that it delivers 100mA (0.1A).

Our bikes have (originally) a 14Ah battery, that means 0.047Ah self discharge per day. Just to maintain the charge you need to put in 0.062Ah daily. The 100mA charge current compensates the self discharge in 0.62h (about 37 minutes).

More assumptions:
The starter motor takes 80A (0.8kW to 1kW motor).

For every second you press the starter button, 0.022Ah of the battery capacity is used. To replace this, the charger must be on for 0.22h (about 13 minutes). The total charge time to compensate the starting is easily calculated: Start button pressed time in seconds * 13 minutes.

With the headlight on and the engine idling, is the battery charged or discharged I don't know, but I have a feeling that you don't need to ride for long to have a positive balance there.

So dare I make the final conclusion: On sunny days the 100mA solar charger may well be enough to start the bike several times a day for a short ride.
I agree the solar charger would work to replace the amps lost during starting, but it would not replace the amps lost due to the drain of the ignition system. As you know our bikes charge very little under 2000 rpm, and on short trips the battery can drop to a 60-70% state of charge.


85 VN700 "Old Yella"

REBUILT ENGINE
CUSTOM PAINT
VANCE & HINES CRUZERS
EAR SHAVED AND RE-JETTED W/K&N'S
DUNLOP ELITE K591 FRONT & REAR
VOLTMETER
SYNTHETIC BRAKE FLUID
SYNTHETIC OIL & GEAR LUBE
PLEXISTAR 2 WINDSHIELD
SPLINES LUBED
ACCT'S GREASED W/TOC SPRINGS
COASTERD
LEATHER SADDLE BAGS
LEATHER TOOL AND ROLL BAG
PICKUP COILS GAPPED AT .018"
NGK CAP, WIRES, IRIDUMS
BARNETT FRICTION PLATES & SPRINGS
CUSTOM GRIPS, MIRRORS, LEVERS
ORIGINAL STATOR & R/R 14.5v
DEKA MF AGM ETX15L

Best Auto/Moto Insurance | Motorcycle Protection Today | FREE Trade-In Quote
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post #7 of 12 (permalink) Old 01-06-2009, 09:09 AM
 
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something i came across

How can I tell if my battery is charged or not?
Lead acid batteries are made up of cells. Each cell is approximately 2 volts, so a 12-volt
battery has 6 individual cells. It turns out that a fully charged 2-volt cell has a voltage of
approximately 2.15 volts. Oddly enough, a fully discharged 2-volt cell has a voltage of
1.9 volts. That’s only a difference of 0.25 volts on each cell from fully charged to fully
discharged. So a 12-volt battery will measure at about 12.9 volts when it’s fully charged
and about 11.4 volts when it is fully discharged. That’s a total of 1.5 volts that represents
the full range of charge on a 12-volt battery. To make a good guess at how much charge
your battery has left, you can assign a percentage of charge remaining that is directly
proportional to the battery voltage. Let’s see how we can do that.
If the battery voltage is 12.15 volts, how much charge is left? Beginning with 11.4 volts
representing no charge or 0% charge available, subtract 11.4 volts from the voltage that
you read. So 12.15 – 11.4 = 0.75 volts. Since there are only 1.5 volts above 11.4 volts
that represents the full range of charge, we can divide the difference that we just
calculated by 1.5 volts to get the percentage of charge remaining. 0.75 volts / 1.5 volts =
0.5 or when expressed as a percentage, multiply by 100 and get 50%.
Here’s the procedure written as a formula that is applicable to 12 Volt Batteries:
OPEN CIRCUIT BATTERY STATE OF CHARGE CALCULATION
% Charge = SOC
% Charge = ((Measured Battery Voltage – 11.4 volts) / 1.5 volts) x 100
Equation 1 Open Circuit Battery State of Charge Calculation
That seems easy enough. So what’s the catch? In order for this formula to work, the
battery must be in a rest state. In other words, the battery should not be supplying power
to any type of load. The experts say that the battery should remain at rest for at least 24
hours to get an accurate measurement, but in a pinch a couple of hours is good enough to
make a reasonable guess. Even if the battery is connected to a load, as long as the load
current is less than 1% of the battery capacity in amp-hours, then this method is probably
good enough in most cases. It’s all a matter of how accurate you want to be. If you’re a
scientist or engineer trying to develop a battery powered product, then you probably want
a more accurate measurement than if you’re going fishing for the weekend and you just
want to know if you need to take the time to charge your battery before you use it.
There is one more thing to keep in mind. The only way to be absolutely sure that your
battery is fully charged is to do a load test. It is best to have the battery dealer do this for
you. We only mention it here because it is possible for a battery to indicate a good
voltage, but then immediately when you try to use it, it acts like it’s dead. This doesn’t
happen very often, but it’s good to know that it is a possibility.


Time Required to Charge a Battery:
Let’s take a moment and talk about two of the fundamental electric quantities, Amps and
Coulombs. A battery stores charge (Coulombs), and an electric current (Amps) is made
up of charge that is moving. Let’s ask a very important question: How long will it take
to charge a battery? If you look at the battery specifications and ratings,
you won’t find Coulombs listed anywhere. What you probably will find is Amp-Hours.
Let’s look at that term. Amps times Hours = (Coulombs per second) times 3600 seconds
(in 1 Hour). So, 1 Amp-Hour = 3600 Coulombs. That’s still sort of confusing. The
main thing to remember is that Amp-Hours and Coulombs are both units that describe an
amount of electric charge.
Let’s try something else. Suppose I have a 50 Amp-Hour battery. That’s a fairly typical
size for an automotive engine start type battery. Now let’s say I have a 10 Amp charger.
If it’s a good charger it will deliver close to 10 amps for as long as it takes to get the battery voltage up to its recharge level. So how long will it take to actually charge the battery?
We can make a pretty good guess by just dividing two numbers:
(Battery Capacity) / (Charger Current) = Time
(Amp-Hours) / (Amps) = Hours
for this example:
(50 Amp-Hours) divided by (10 Amps) = 5 Hours.
So we would estimate that it will take a good 10 Amp charger about 5 Hours to recharge
a 50 Amp-Hour battery. Actually this rough estimate usually tells us how long it
takes to recharge the battery to about 80% of its capacity. It turns out that it will
probably take an equal amount of time, or another 5 hours to recharge the last 20% of the
battery capacity.

Last edited by dutter; 01-06-2009 at 09:17 AM.
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post #8 of 12 (permalink) Old 01-06-2009, 09:17 AM
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Quote:
Originally Posted by pappa View Post
Some hypothetical calculation, just for the fun of it.

Assumptions:
Lead acid battery self discharge is less than 10% per month, but let's assume it is 10%.
Lead acid battery efficiency is 75% or more, but let's assume 75%.
125mA from the solar cell charger probably is in optimal conditions, so let's assume that it delivers 100mA (0.1A).

Our bikes have (originally) a 14Ah battery, that means 0.047Ah self discharge per day. Just to maintain the charge you need to put in 0.062Ah daily. The 100mA charge current compensates the self discharge in 0.62h (about 37 minutes).

More assumptions:
The starter motor takes 80A (0.8kW to 1kW motor).

For every second you press the starter button, 0.022Ah of the battery capacity is used. To replace this, the charger must be on for 0.22h (about 13 minutes). The total charge time to compensate the starting is easily calculated: Start button pressed time in seconds * 13 minutes.

With the headlight on and the engine idling, is the battery charged or discharged I don't know, but I have a feeling that you don't need to ride for long to have a positive balance there.

So dare I make the final conclusion: On sunny days the 100mA solar charger may well be enough to start the bike several times a day for a short ride.
Well, on paper (or the screen) then, it sounds like it'd work


AKA: Tim & 'The Adventure Cycle' VROC #24567, NEVROC, SteelCity VROC


"When life throws you curves,
Aim for the apex."

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post #9 of 12 (permalink) Old 01-06-2009, 11:21 AM
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Quote:
As you know our bikes charge very little under 2000 rpm, and on short trips the battery can drop to a 60-70% state of charge.
Hmm.. I measured the battery voltage when the engine was idling and headlight on not so long ago, and it was around 13V. So not discharging. On the other hand I know nothing about the history of my bike - maybe the stator has been replaced to a more efficient one..
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post #10 of 12 (permalink) Old 01-06-2009, 11:34 AM Thread Starter
 
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the reviews on this charger are real good and some of them say they use em to charge up their motorcycles but i just have a hard time believing it can do any good in a short period of time at .125A. theres some real good information here though, thanks guys!
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