Battery Pack/power Supply

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Oct 30, 2000
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#1
Guys

i've got a little project ive been meaning to sort out for some time. i'm in aust and our xrs have full lights ect but no battery.

problem is that i'm sick of forking out for batteries for my gps & running out of battery power for my uhf radio. it seems silly to have 12v & heaps of power when the motors running but run everything off external batteries.

as a result, i want to power my gps (magellan 2000xl) & my uhf radio both at the same time & both powered off the bike.

the gps needs a constant smooth 6v and the uhf needs intermittent high draw 7.2v.

so what i'm looking at is making up a 7.2v battery pack (6 nicad AAs) with a take off at 6v (5 AAs) for the gps. easy

i also need to solder up a charger that will take 12v off the bike and keep the AAs full without conflicting with the draw of the gps &/ uhf.

will this work? can i trickle charge the nicad pack as a group while sucking power out of them at the same time??

does anyone have any advice or know a good electronics site that'll have a charger & isolater circuit diagram for me or do i need to sort out a 12v battery pack and charger and build some transformers to reduce the 12v to 7.2v & 6v respectivly.

thanks

hs
 

dbd

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#2
I don't think it will be possible to charge and use either item at the same time .I think you'ld need to have two sets of batteries for both . A step down transformer would do the trick , but the first thing that comes to mind is the weight of these units .My two cents ,good luck .

dbd
 
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#3
Your best bet I think is to get some good RC 7.2V race batt packs form Radio Shack. You can get NiMh packs with up to 3000 Mah capicity that will probably last you the whole weekend. Radio shack also sells 12V DC cahrgers for theese RC car packs. Keeping two batt packs with you should be more than enough, and you can have a 6V take off by puttng a lead on the 7th cell of the 8 cells to drop the 1.5 V.
The problem with trying to charge or run stuff from your bike is the power is dirty. The voltage goes up and down as the bike revs and the power often has an AC ripple in it as is the nature of the magneto genarator. No big deal for the lights but a problem for sensitive electronics. You would need to filter the power to nice clean DC and then regulate the voltage. DC battaries are great for regulating the voltage as they will keep it up when the input is down (low RPM) and help drag the voltage down when it goes up, like a buffer. A voltage rectifier and or regulator can be made, but why not tear the components form an old car alternator? The rectifier regulator is usally built into a unit in the back of the alternator, the ones the charge wires come out of. 12V is ok charge voltage for 7.2V batt pack, and with the low input power form the bike, you shold not hurt it, but try to find regulateor with an adjustment to lower the V max to around 9v or so.
Also, an AC to DC wall plug in adaptor could be used nice and small, light and cheap. Try to find a solid state switched type and not a transformer one. If you have an old computer power supply youve got a winner :) . The problem with a transformer is it has a set step down rate. So in the states we use 120 Vac in the house so a 9 to 1 step down is used to get the 16V or so ac to clip down to 12V DC for a 12V DC adaptor. The step down is consistant reguardless of the input, so if you put 10V AC into a 10 to 1 Xformer you get one volt ac on the secondary coil :( . This is not good for a varing input voltage range as is the case with the bike but works fine for regulated house line voltage.
One other option is to use the radio shack charger itself for the job. If it can take the max input voltage and by its designe will filter and regulate the output. Use the charger with a 7.2V batt pack to make your mini powersupply. You will have to check the power out as I am not sure how good of a filter is in the charger as it is made to run from a 12V DC car system. You may have to make or by a full wave brige rectifier and a clipper to keep the input voltage down, You will have to mesure the max voltage the bike puts out a full throttle. A retifier is just 4 diodes aranged in a dimond config to turn AC to DC. Radio shack sells intigrated high current and High V ones for like 3 bucks.
If I were you I would try the high capcity RC batt packs and see how long they run your stuff. If the durration is acceptable then just use the recargable packs and forget the on board charger. The duration of course depends on the avarage current draw of your avionics :) and the capicity of the cells used in the pack. The more expensive packs have larger capcity, the capcity rating is Mah, mili amp hours, and the Nicle Metal Hydroxide, NiMh cells are better thatn the Nicle Cadium, NiCad cells.
Good luck :) . Hope that helps a bit.
 
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#4
Some of the other fellows information may be not quite appropriate, i.e mixing 60 Hz wall a.c. voltage transformations with higher varying frequency bike alternator voltages and assuming 1.5 v per Nicad. Nicads vary from 1.4 v full charge to 1.1 v near dead.

Here's your plan. Get a full wave bridge rectifier chip good for about 100 V and 20 amps (lots of safety margin) and connect it to your headlight power. Then connect it to an about 40 volt multi thousands of uF dc capacitor and there's a bit of a dc supply, very unregulated between about 10 v and probably 14 v. Now take this and feed an LM317T regulator chip, adjusted to the voltage you want plus about 0.6 volts because we're going to take the 317 output and go through a silicon diode to feed a dicky little battery pack for your device. The battery pack will not be "charged" since charge voltage is higher than running voltage, but it will act as a filter and will be maintained from dropping in voltage. When the alternator pukes with low voltage, the batteries will keep your device running. When the alternator voltage is up, you run off of the LM317 diode battery chain with a VERY clean dc supply. You can look up the LM317T data sheet on the web at national semiconductor, it's very informative.

The batteries would be your most expensive part. You could get AA's or smaller with no need for big capacity since they won't do much. Only caveats: if your radio hogs power on Tx, the 1 amp capacity of the 317 may not be enough. You should test that with an ammeter and then get a higher current rated dc regulator chip instead of the LM317T. You may want to heat sink the 317's as well if you pull any amount of juice towards 1 amp in your GPS etc.

If this seems greek to you, you probably shouldn't be trying to make your own stuff and should get a dc-dc adaptor directly intended for yoru radio and your GPS, ie like for a car cigarette lighter socket. Then you might still have to add the bridge rectifier chip and capacitor if your headlight gets AC and your bike has no battery (to give dc to the "cigarette lighter " socket you effedtively would be creating on your bike, to plug the store bought gizmos into).

The Nicads may not be fully happy with no raised charge voltage, as lead acids might also not be, so an alternate plan is to rectify your headlight power into a 12V lead acid battery(instead of the capacitor), and then feed the LM317's off that. Then you'll have no voltage droop unitil the lead acid battery really gets discharged (i.e. 9v). warning: don't try to use a Nicad directly as they have charging quirks that could lead to a meltdown of the battery pack. Lead acids get charged this way all day long in cars and bikes and live happily with it.

Good luck :)
 
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#5
I still say for get on board charging and go with the recargable NiCad packs. Radio shack sells Voltage regulaters too than can handle more thatn 1 amp but need heat sinks. I dont think your looking at more than an Amp here, but like he said, you gatta measure it. As far as the voltage drop of the nicads, its really not practical as the voltage of the cells only really drops under heavy discharge, like 30 to 40 amps. The off the shelf batts you put in the thing have the same properties as they discharge.
I like the idea about the battary filtered rectifier, with the battaries in the line you shold not have to worry about exceeding the 1 amp of the regulator, but like he said, if you have to ask about any of this stuff, I would go with the NIcads. I use em for everything from GPS to radios. I have loads of em around cause I fly electric RC planes. Just charge em off your car, take 2 with and ride all weekend :) .
 

TexKDX

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#6
Helterskelter,

If you want to construct your own battery pack, my suggestion is you hook up with your local radio control hobby shop. Lots of planes, boats, and cars are electric these days. These guys are used to making their own from available raw materials.

Same for the local ham radio club. These guys are always putting together high power/low cost batterys for their handy-talkies.

Funny you bring this up. I've been doing GPS research all week. The plan is to use a 12v DC power source and let the GPS internal or the adapter cable do the conversion for me to what the GPS needs.

One source for batteries is your local home security supply shop. All alarm panels these days have a battery backup in them to keep from losing the program during power interruptions and provide functionality during interruptions. I picked up a 12v sealed gel cell the other day for a friend's '95 KTM 400RXC. The dealer wanted $76 for the battery. I got it for $11.26. It is small enough to fit in the airbox or sit in the bottom of a cyco active glove box no problem. I have not done the math yet (amp-hrs vs. 2 1.5 dry cells) but suspect the gel cell will last the life of 12-14 sets of dry cells. This should be enough to get me thru week long dual sport adventures.

If you'd like to create a 12vdc souce on your bike, call Baja Designs and have them ship you a 12v regulator/rectifier. It will regulate current to 13.8vdc (charging voltage for a 12v battery - 12 volt systems are really 13.8 volt systems) from your existing stator. I'm a little foggy on the wiring, if it should go before or after your existing regulator and if both phases need to be charged on the input, so let me call them next week and talk it over.

The unit costs about $25 from them. I've installed 2 of them with no problems and they ship them with their 12v DC kits.
 
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#7
good info - thanks

weekends are ok to carry batteries. the power supply idea was really for our multi week rides into no mans land. we ring ahead to stations for fuel & water or gps into roadhouses but like to be self sufficient for all else. nothing worse than getting to a fuel point only to find they only have 1 pack of poxy old sunbleached std batteries.

i was going to build a LM317 circuit that should be enuogh to look after the gps but it wont put out enough for the uhf. also when i turn the bike off there'll be no power & i'll loose all my waypoints ect. as a result batteries of some form are necessary.

i spose the easiest option is to have a 12v battery/pack and reduce it from there or to use one set of nicads to run everything whilst another set is being charged on the bike and then swap when needed.

is it possible to both constanly charge & intermittently draw from nicads or other sorts of small batteries (RC, phones, ect)

thanks
 
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#9
Hi Helterskelter400,
You can charge either SLA or NiCad on the bike when it's running, with simple rectification from your existing 13.8 volt a.c. system (you have a 12v bulb headlight, right?). However, the NiCad can improperly charge due to it's unique charging characteristics, wheras a SLA battery can't go wrong. They both drop in voltage as they discharge, and no, I'm not talking about internal losses drop from running a heavy load like 40 amps. What I mean is that if you expect 20 hours run time without getting some charge from the running bike engine, by hour 19 the voltage will have dropped siginificantly, with 10 volts being the furthest you'd want to take either pack. You can go NiCad if you put a series resistor parallel with a diode to limit the charge current when the bike is running. SLA doesn't need that. And when your bike's off, think of it as running your car radio with the key in the accessory position, it's the same thing. Hopefully your GPS is smart enough to revert to it's internal batteries when you unplug the adapter from the wall or the cigarette lighter. That's if you put a siwtch in or completely kill your battery pack. Elsewise, it'll simply always be powered up.

Yes, either battery pack can be "charged at the same time as it runs the dc regulators (which run the gizmos)". What's actually happening is the current flows mostly to the dc regulators instead of into the batteries, and only flows somewhat into the batteries if they are in a low voltage/discharged state. Same as how a car works, you can watch an ammeter that shows the battery discharging at idle (-ve current) with all the accessories on, and charging again (+ve current) when the engine revs up again off idle. When the battery is fully charged and the motor's revving, the ammeter shows zero current (ammeter to battery +ve terminal to car +ve power rail).

For reliability and peace of mind, go with SLA. If you can risk a battery pack meltdown, go NiCad. Been there, done that. You won't need the Baja regulator, your bike already has one, you just need a rectifier. Do this setup and you'll be good for a many week trip, no chargers required, just as how cars operate charging themselves. Only caveat is size the battery pack reasonably, i.e. don't expect a volkswagon beetle battery to run a competition stereo all night, or don't expect a micro pack to power the GPS for 3 days of parked time. Just calculate mAmps draw x time expected to run and that's mAmphours, or amp hours if you use those units. Then get a pack with cells rated for that and you're done. If you want a smaller, lighter pack you just have to restrict or shorten how long you leave your bike off, between running it and getting the pack recharged.

Just so you're clear: existing headlight a.c. into rectifier, that d.c. into SLA, SLA into LM317 (or other chip), chip output into GPS. If NiCad, put a power resistor between the rectifier and the NiCad, rest is same. For the radio, find another regulator chip that can handle the amperage and hang it off the SLA or NiCad too. Your safest, least difficult bet for the LM317 role is to get a car cigarette lighter adapter for the GPS and for the radio, and hang them off the SLA, which is the same thing as if they were plugged into a cigarette lighter socket. Wire the regulator gizmos directly to the SLA and the power won't go away when your bike engine stops running, only the charging stops. You don't need to swap packs, having one charging and one being used.

Good Luck!

TexKDX, as far as I know the Baja Designs electronics are simply 2 wire snowmobile ac shunt regulators, as I needed one in a pinch and got a snowmobile part that was indistinguishable from my original. However, they are ac, not dc. Hence the need for a rectifer. An alternative would be to get a dc combo from Electrex, as Will Pattison pointed out some time ago, but there's some $ involved then.
 

TexKDX

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#11
Originally posted by techman

TexKDX, as far as I know the Baja Designs electronics are simply 2 wire snowmobile ac shunt regulators, as I needed one in a pinch and got a snowmobile part that was indistinguishable from my original. However, they are ac, not dc. Hence the need for a rectifer. An alternative would be to get a dc combo from Electrex, as Will Pattison pointed out some time ago, but there's some $ involved then.
Think again, "TECH"-man. I know the difference between the two and they sell both. I replaced the blown stock reguator-rectifiers on two '95 KTM RXCs which use a DC lighting system and flasher with the units from BD. I also have one of the units you are referring to sitting in the tool box. The regulator/rectifier version is about three times the size of the plain regulator.

If you still don't believe me, give them a call and ask them.
 
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#12
Check out the RC batt packs at Radio shack. They make the new ones out of NiMh and they are the same size and higher capacity as NICad. They also dont have "memories" like NiCad and very high charge input current ratings so they are ideal for short duty cycles, discharge while charging and Wayyyyyy lighter than sealed lead Acid SLAs . Last time I looked they were like 25 bucks a pack at radio shack for 1800 Mah packs. I just got some of the new hot CP1300s off the internet for 35 bucks per 9.6V 8 cell packs. The CP 1700s are even hotter and longer lasting but I fly RC jets so cell pack weight must be carfully considered hence the 1300s for my current project.
 
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#13
Hi TexKDX,
My apologies for not knowing that Baja has dc units as well, I didn't pay attention to your post. Yes, I believe you and I read your posts often and respect your info. :) I got my E-Line a few years ago and they may not have had them then, or I would have asked for it had I known. However, for HS400, his bike already has the regulated ac, so he would/could replace his existing ac regulator if he wanted, but more economically, the rectifier is about $1 at a surplus store, plus then he doesn't have to mess around with phasing and disconnecting his original bike wiring. I agree that he should get the $11.26 security supply shop SLA gel battery. The retrifier I used was the same package size as the BD Ac unit, so I inadvertently ended up with a smaller setup than the BD dc unit.

I'm not sure about how NiMH batteries like an automotive-like charge/use environment. I wouldn't trust them without some research into their charge/discharge cycle characteristics. In passing, I've heard stories about exploding NiCads (my friend with a hobby store points to a hole in his ceiling related to one story). I've melted one pack with a malfunctioning charger. $100 of oops there. No stories yet about NiMH because few people regularly use them. BTW I'm an EE, that's why I am interested in this thread.
 

TexKDX

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#14
Thanks for the response, Techman. Yea, you hit in an area that I'm curious about and was planning to do research in - that of overcharging batteries with the bike's electrical system. I always wondered about that on the '95 RXC's system. The same applies when you add a battery to an enduro bike's simplified system. I understand bleeding off the excess voltage above 13.8 volts, but not how the wattage is dealt with.

It must go SOMEWHERE, right? For example, on my KLR it has like a 130 watt output stator, yet drives a 55 watt headlight and 5 or 10 watt tail light, plus charges its battery. How does the system keep from overcharging the battery, watts-wise? Why don't the bulbs blow from excess wattage, even with the volts are kept at 13.8 or less? I assume the same principles apply for household current - lots of extra watts available there you know...

Any EE insight would be appreciated, either here or via email. Thanks,