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Best Way to charge gel 7a 12v on way to field?

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Best Way to charge gel 7a 12v on way to field?

Old 10-05-2005, 08:07 AM
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speedster 1919
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Default Best Way to charge gel 7a 12v on way to field?

I have a van and keep my planes and field equipment in it all the time. My flying time is not planned most of the time since I'm on the road as a salesman. If I decide to fly ,I want to use my rear lighter outlet to charge my 12v gel battery on way to the field ,about an hour. If I just put a cig lighter plug with alligator clips ,will my car charge the battery safely while I drive or would it be better to get an 110v inverter and plug in my wall wart charger for the 1 hour I drive. The car charge rate could be potentionally be 40 amps and I don't want to gas or overcharge my gel battery inside my field box.
Old 10-05-2005, 08:26 AM
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Mad Wax
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Default RE: Best Way to charge gel 7a 12v on way to field?

If you plug the cig. lighter straight into your acid battery it'll damage the battery, if not explode or split. You need to regulate the charge output. Some van/truck outputs are 24v also. To fully charge that battery (from flat) in one hour approx 7A charge which is very high also for all battery types. Probably best to use a slower charge but start the charge before you leave, or perhaps the night before (if it's a NIMH 1A charge with delta peak shut off before you go to bed and it'll be done by next morning)

If it's a lead acid battery they don't take kindly to fast charges, so I would possbily use a slow charge once it's topped up it continues with a very slow trickle charge (can be left trickling 24/7) however it'll probably eventually flatten the van battery
Old 10-05-2005, 08:42 AM
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speedster 1919
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Default RE: Best Way to charge gel 7a 12v on way to field?

Thanks for the reply. I know the rear plug is not 24v and the gel battery will not be fully discharged. I basicly want to top up the charge as I drive to the field. The charge wall wart is about 1/2 amp and will do this safely , maybe pluged into an 110v inverter with lighter plug for cars. I think !!!!!
Old 10-05-2005, 10:38 AM
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Default RE: Best Way to charge gel 7a 12v on way to field?

Mad Wax,
If you plug the cig. lighter straight into your acid battery it'll damage the battery, if not explode or split.
If the gell cell is charged there is no problem. Put a 1 amp fuse in series with the cig. lighter for protection and you are good to go. this is exactly how I keep my field battery charged.

John
Old 10-07-2005, 12:32 AM
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AS-EE
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Default RE: Best Way to charge gel 7a 12v on way to field?

Please remember people to include a fuse as Jnorton has stated above because if your gell cell battery has less voltage than what is being supplied at the cigeratte lighter socket then you will have huge current flowing through the wires to the small gell cell battery. It is safe, however to hook up a Gell cell battery if it is charged because it will have the same voltage potential as that being supplied by the cigeratte lighter socket and thus there will be a net voltage drop across the wire's resistance of zero and therefore 0 amps of current flow.
Old 10-07-2005, 06:59 AM
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speedster 1919
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Default RE: Best Way to charge gel 7a 12v on way to field?

That way still sounds iffy.........So to play it safe I went to Harbor Freight and bought a 110v converter and pluged in my Hangar 9 wall field battery charger. Seams to work OK. The inverter is suppose to shut off if car batt gets to low. Funny but my cig plugs only works when van is running......... Also I checked the price of the inverter off the net from Harbor Frieght and it was $19.95 at the store it was $29.95. I asked why the big difference in price and was told I was paying for the store front. But I could go home order and pay the frieght for $19.95.
Old 10-07-2005, 07:43 AM
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Default RE: Best Way to charge gel 7a 12v on way to field?

Also I checked the price of the inverter off the net from Harbor Frieght and it was $19.95 at the store it was $29.95. I asked why the big difference in price and was told I was paying for the store front. But I could go home order and pay the frieght for $19.95.
Carry the printed copy of the web page and they will sell it to you for the same price. Always check the web. Harbor Freight bears watching.

Bill
Old 10-07-2005, 10:44 AM
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Default RE: Best Way to charge gel 7a 12v on way to field?


ORIGINAL: speedster 1919

That way still sounds iffy.........So to play it safe I went to Harbor Freight and bought a 110v converter and pluged in my Hangar 9 wall field battery charger. Seams to work OK. The inverter is suppose to shut off if car batt gets to low. Funny but my cig plugs only works when van is running......... Also I checked the price of the inverter off the net from Harbor Frieght and it was $19.95 at the store it was $29.95. I asked why the big difference in price and was told I was paying for the store front. But I could go home order and pay the frieght for $19.95.
So you take 13.8 volts DC from the automotive system convert it to 120 VAC and then convert it back down to 13.8 volts VDC. [] Sometimes it helps to think about what you are doing. Again I say the field box battery doesn't know where it getting its voltage from and doesn't care.

John
Old 10-08-2005, 08:32 AM
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speedster 1919
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Default RE: Best Way to charge gel 7a 12v on way to field?

Hi John I know that sounds whacked to convert back to 13.8 volts but on some vehicles it could be 14.2 - 14.5 The vehicle battery being larger will set the initial charge rate of probably 15 amps to replace starter usage . I was not sure the 7 amp gel cell was smart enough to take just the 1/2 amp it would need. The 1 amp fuse in line with a cig plug sounds safe , but I wanted a inverter anyway...............Right now I know I am safe with the Hanger 9 12v charger. My tower .75 needs all the juice for the sullivan starter it can spare. That is a tight ABC engine.
Old 10-09-2005, 07:42 AM
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Default RE: Best Way to charge gel 7a 12v on way to field?

Now I understand!
The vehicle battery being larger will set the initial charge rate of probably 15 amps to replace starter usage . I was not sure the 7 amp gel cell was smart enough to take just the 1/2 amp it would need.
Current will split between the two batteries depending upon their state of charge. If the gell cell is charged it will draw a minimal amount of current even though the alternator is supplying 30 amps to charge the car battery. Exactly like AS-EE posted.

John
Old 10-09-2005, 08:35 AM
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JimTrainor
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Default RE: Best Way to charge gel 7a 12v on way to field?

The only problem I see with the fused direct connect is that if the 7 Ah gell cell is significantly discharged it might draw more than one Amp and then the fuse will blow. Then you'll be left with an uncharged battery... which would defeat the whole purpose.

You could discharge your battery then measure the max current when you connect it. Even with a measurement to see what's happening, I think I'd just hook up the battery and fuse and see what happens. The fuse will protect the battery (and car). If you find it never blows, then I'd say your fine. You might want to carry a spare fuse with you figure this out.

If somebody knows the internal resistance of a 12 7Ah gel cell we could figure out the answer.
Old 10-09-2005, 09:18 AM
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Default RE: Best Way to charge gel 7a 12v on way to field?

I just measued by own 7 Ah gel cell. This is what I measured using a Hanger 9 charger (nominally 12V/600mA):

battery voltage no load: 13.4 V (it is fully charged)
charge voltage when the Hanger 9 charger is attached: 15.2 V
charge current: 300 mA

(p.s those number don't make complete sense to me...they say that batteries internal resistance is 6 ohms. higher than I would have guessed?)

So... If I connected this to 13.8 volts the current would be lower.

Repeating the excercise with a discharged battery would be more informative. (But I don't have any easy way to discharge my battery at the moment.).

If you do try the direct connect to your car, and the fuse blows, a resistor in series would limit the current. But if you're uncomfortable with it, don't sweat it. Just get the inverter.
Old 10-09-2005, 06:25 PM
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Default RE: Best Way to charge gel 7a 12v on way to field?

I just measued by own 7 Ah gel cell. This is what I measured using a Hanger 9 charger (nominally 12V/600mA):

battery voltage no load: 13.4 V (it is fully charged)
charge voltage when the Hanger 9 charger is attached: 15.2 V
charge current: 300 mA

(p.s those number don't make complete sense to me...they say that batteries internal resistance is 6 ohms. higher than I would have guessed?)

So... If I connected this to 13.8 volts the current would be lower.

Repeating the excercise with a discharged battery would be more informative. (But I don't have any easy way to discharge my battery at the moment.).

If you do try the direct connect to your car, and the fuse blows, a resistor in series would limit the current. But if you're uncomfortable with it, don't sweat it. Just get the inverter.






A battery at a voltage potential of zero is practically a dead short circuit and tons of current will flow through it. I hope you realize that the power produced will be substantial and the battery will get hot instantly and could lead to serious injuries. So even if you had a 13.4 charge voltage you will STILL need a way to limit current. Also it's not very wise to discharge a lead acid battery completely as this will ruin it.



Old 10-09-2005, 06:39 PM
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Default RE: Best Way to charge gel 7a 12v on way to field?

I got the inverter and it worked perfect on way to the field and I might add I feel safe this way. I checked the Hangar 9 charger and it is 600 ma..............
Old 10-09-2005, 06:45 PM
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Default RE: Best Way to charge gel 7a 12v on way to field?

A battery at a voltage potential of zero is practically a dead short circuit and tons of current will flow through it. I hope you realize that the power produced will be substantial and the battery will get hot instantly and could lead to serious injuries.
A dead lead acid battery is still at 11.8 to 12 volts potential you cannot get one to zero volts.

The whole premise is that you start with a charged field box battery use it at the field and charge it back up connected through a fuse to your cars 12 volt system. It is safe it will NOT cause the battery to explode and I have yet to have a fuse blow. Let's inject some reality here!

John
Old 10-09-2005, 06:59 PM
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Default RE: Best Way to charge gel 7a 12v on way to field?

Thanks Jim I knew it wouldn't explode......... I just didn't want it to gas sitting right under my field panel and corroding everything............
Old 10-09-2005, 07:14 PM
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Default RE: Best Way to charge gel 7a 12v on way to field?

A dead lead acid battery is still at 11.8 to 12 volts potential you cannot get one to zero volts.

The whole premise is that you start with a charged field box battery use it at the field and charge it back up connected through a fuse to your cars 12 volt system. It is safe it will NOT cause the battery to explode and I have yet to have a fuse blow. Let's inject some reality here!


I never said that it would explode under a dead votlage of 11.8 to 12 volts. I did say it could cause injury if you had a lead acid battery at a voltage potential of zero volts, and if you read my post #13 then you will see that I agreed with you on using a fuse inline if one wants to maintain the battery.
Old 10-09-2005, 07:23 PM
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Default RE: Best Way to charge gel 7a 12v on way to field?

I did say it could cause injury if you had a lead acid battery at a voltage potential of zero volts,
LAST post it. It is impossible for a 6 cell lead acid battery to EVER get a voltage potential of zero volts. What part of that don't you understand!!!!!

If the batter4y get below 11.5 volts it is shot and won't accept a charge hence absolutely no potential for your theoritical explosion. PERIOD
Old 10-09-2005, 07:31 PM
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Default RE: Best Way to charge gel 7a 12v on way to field?

Buy a Litco Alpha 4 and charge every battery you have on your way to the field... good luck getting them though. They have been on backorder for over a year. I got luck and got mine off of eBay. http://home.att.net/~LitcoSys/indx.htm
Old 10-09-2005, 07:32 PM
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Default RE: Best Way to charge gel 7a 12v on way to field?

It is impossible for a 6 cell lead acid battery to EVER get a voltage potential of zero volts. What part of that don't you understand!!!!!
I was under the impression that speedster 1919 wanted to somehow kill his battery to 0 and measure the internal resistance. You cannot measure resistance in an energized circuit ever!

Repeating the excercise with a discharged battery would be more informative. (But I don't have any easy way to discharge my battery at the moment.).
This is what he wrote down. It does not make sense because he states in parenthesis that he has no easy way to discharge the battery when as you stated its discharged when its 11.8 to 12 volts. I was under the impression that somehow he wanted to totally kill his battery if possible and measure its internal resistance.[:-]
Old 10-09-2005, 07:43 PM
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Default RE: Best Way to charge gel 7a 12v on way to field?

Calm down you two before you blow your battery caps. I did that once in my youger days and got a cap in each eye followed by acid. I would not recommend this exercise. I did not say I wanted to discharge the battery.............
Old 10-09-2005, 07:47 PM
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Default RE: Best Way to charge gel 7a 12v on way to field?

Wait a sec. JimTrainor said that lol. I accused the wrong person. My bad..
Old 10-09-2005, 07:52 PM
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Default RE: Best Way to charge gel 7a 12v on way to field?

How much current a 12v battery will take during a charge relates to the charge voltage as well as the discharge state of the battery. A fully charged lead-acid battery (either gel-cell, wet-cell, AGM, etc) will exhibit a fairly high internal resistance when attempting to charge.

Any voltage less than 12v can be considered fully discharged, the resting voltage of a battery will be about 12.65 volts when fully charged. The resting voltage is measured after disconnecting from any charger or load, and left sitting for 24 hours. If you measured 13.4v on it, you had just recently disconnected it from a charger and it was still showing a surface charge.

A gel-cell battery that is in a discharged state can be safely charged at 14.4 volts and will take a reasonably high current (probably a couple of amps for a 7ah battery) without a problem. The problem is that once a fully charged state is reached, 14.4v is too high and will start to boil the electrolyte, causing pressure to build inside the battery. This can happen even if the charge current is less than 100ma. 13.5v would be a more reasonable charge voltage for long-term, but will not be enough voltage to do much charging in a one hour period.

What the best solution would be is to use an intelligent multi-stage charger, but you would probably only find one that operates from 120v AC, and you are back to using an inverter.

If it were me, here is what I would do. I would rig up a 12v cigarette lighter plug to a pigtail like you suggested, but instead of a fuse, I would use an automotive light bulb, say an 1141, that would limit the current to less than 1 amp. Even if you directly short the line, the worst that would happen is the 12v bulb will light up, and you would be drawing about 1.4 amps. Just make sure you put the bulb in the positive side of the pigtail! Most vehicles may start out at 14.4 v when started, but usually taper down the charge voltage some after running for a while. Even if the voltage stays above 14v, for one hour it should be fine, and the 12v bulb will have some voltage drop across it even when cold.

The reason the 12v bulb works in this case is that the resistance is not linear. The resistance is fairly low when the filament is cold, the resistance will increase as the filament warms up. The old Kraft battery chargers used bulbs to limit the current as well as indicate charging. They sold different bulbs for different charge rates.

Bob R.
Old 10-09-2005, 08:11 PM
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Default RE: Best Way to charge gel 7a 12v on way to field?

Now that is stupidly simple and it works!! You are applying the basic laws of the postive temperature coefficients of a conductor's resistance. Good job!! I would not have thought so simple in design. I would have taking the Zener diode approach connected to a transistor and with a relay disconnect setup.
Old 10-10-2005, 05:55 AM
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Default RE: Best Way to charge gel 7a 12v on way to field?

By discharged I didn't mean dead. I meant discharged! ... as in, needs to be charged!

The numbers I posts were indeed right after taking the battery off the charger.

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