on-board charging

[bluesy]

Hey guys........

I am mulling around the idea of on-board charging my battery. I know I can mount a jack in the battery leads but I'm unsure whether or not I need to isolate the ESC during the charging cycle. I suppose a DPDT switch would do the job but I'd rather not do it if I don't have to.

thanks for any advice.

Doug

[Kmot]

http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXL303&P=0 :D

[bluesy]

Thanks for the reply, Tom. I should have made myself clearer as to what I needed. I won't be using a receiver battery. I want to charge the 7.2 volt main battery. It will be supplying both the motor power and the receiver power (through the BEC).

Thanks again

Doug :confused:

[LtDoc]

Doug,
One alternative is to use a jack that has a switch built into it which disconnects the load side of the system when the charging plug is inserted. No idea where to find one new, happened to have one from something else. They shuldn't be ~that~ hard to find though.
- 'Doc

[steveciambrone]

Just disconnect the battery and charge the battery at the battery connector. If you do not have a switch or disconnect the battery the radio will always be on discharging the battery.

Steve

Thanks for the reply, Tom. I should have made myself clearer as to what I needed. I won't be using a receiver battery. I want to charge the 7.2 volt main battery. It will be supplying both the motor power and the receiver power (through the BEC).

Thanks again

Doug :confused:

[patmat2350]

Most make/break jacks DO NOT have a lot of amp carrying capacity- audio style jacks are typically rated arounded 1A or less. You'd like to fast-charge high capacity NiMH and NiCds at around 3A or more.

Pat Matthews

[ScottOram]

My VANTEC ESC specifically states that you should isolate the ESC from the battery when charging.

[bluesy]

Scott.....

Thanks for that input. I certainly don't want to fry an ESC. I guess I'm going to have to come up with some kind of switching arrangement to isolate the battery from the rest of the electronix.

thanks again

Doug

[LtDoc]

Doug,
'Steve' had about the simplest method, hopegully there's a battery connector that you can reach. 'Pat' is also right, the 'average' "make/break" type jack won't carry much current. Luckily, the one I used wasn't the 'average' jack, but it certainly wouldn't be worth what you'd have to pay to scavenge one from the same place I did. Ones heavy duty enough to handle the required current are available if you can find them, though.
A 'DPDT' switch isn't necessary. A simple 'SPST' switch will work just fine, if it's placed between the charging jack and the ESC. Both (+) and (-) don't need to be 'opened', just one of them (parallel the jack, series the switch).
Good luck.
- 'Doc

[bluesy]

Thanks Doc for the advice. Shoulda known both sides don't need to be switched.......duh. I've been away from my former career (fiber optic-telecom) for too darned long. Just getting back into the basics of electronix again.

thanks again

doug

[Kmot]

Doug, the point of my post was that all you need is a three-way harness with a switch so you can isolate your battery and plug in your charger by switching off the switch. ;)

[bluesy]

Thanks .Kmot...........

I get the picture now. Getting a little slower as the years march by. Thanks a bunch for your advice....

later

Doug

[DanL]

A long question -
I onboard charge two parallel wired 7-cell (8.4v) Nicad packs. The packs are wired and switched to charge separately and isolated from the ESC, etc. Each pack is about 2Ah.
I charge at a max of 1A, assuming that will keep the batteries from overheating since they are buried low in the hull below a lot of accessory stuff. Then I read that Nicads should be charged at 3C for most efficient charging. That would be 6A for the 2A packs. (My charger only goes to 5A). What is the best charge rate to get efficient charging and to keep the batts from getting too warm? (I don't necissarily need a fast charge.)
thanks,
Dan

[steveciambrone]

You really need to charge them individually for the best charge and to prevent them from becoming unbalanced. Eventually a pack will become unbalanced and cause premature charge termination and overheating of the pack that is fully charged. All the literature on Nicad charging says not to parallel charge.

Thanks
Steve

A long question -
I onboard charge two parallel wired 7-cell (8.4v) Nicad packs. The packs are wired and switched to charge separately and isolated from the ESC, etc. Each pack is about 2Ah.
I charge at a max of 1A, assuming that will keep the batteries from overheating since they are buried low in the hull below a lot of accessory stuff. Then I read that Nicads should be charged at 3C for most efficient charging. That would be 6A for the 2A packs. (My charger only goes to 5A). What is the best charge rate to get efficient charging and to keep the batts from getting too warm? (I don't necissarily need a fast charge.)
thanks,
Dan

[DanL]

Steve,
The packs are wired to charge individually, not together in parallel. So I charge two separate packs after each boat outing. Each pack is 8.4V, 2Ah. They are wired thru a switch that puts them in parallel to feed the boat motor, etc. so that I get 8.4V with 4Ah capacity in the "on" position.
So - still the question - what's the best charge rate for "cool' charging. I have a digital charger with settable charge rate and auto cut-off.
Thanks,
Dan

[Elroy68]

reevaluate answer.

[steveciambrone]

3c for the recommended rate or as close to it as possible, as part of the fast charge, the cells should be slightly warm at the end of the charge. even at a C10 rate 200ma the cells will still be warm after a 16 hour charge.

Thanks
Steve

Steve,
The packs are wired to charge individually, not together in parallel. So I charge two separate packs after each boat outing. Each pack is 8.4V, 2Ah. They are wired thru a switch that puts them in parallel to feed the boat motor, etc. so that I get 8.4V with 4Ah capacity in the "on" position.
So - still the question - what's the best charge rate for "cool' charging. I have a digital charger with settable charge rate and auto cut-off.
Thanks,
Dan

[DanL]

"even at a C10 rate 200ma the cells will still be warm"

Steve,
Sorry I seem so dense, but are you saying C10 is 200ma? The pack is 2Ah, so I thought that C1=2A. Then C3 would be 6A, which sounds really high to me.
Thanks,
Dan

[ScottOram]

Here is a Link to the VANTEC 411 ESC, Page three of the manual has a good wiring diagram to isolate the ESC and install an onboard charging jack.

http://www.vantec.com/retman98d.pdf

[bluesy]

Scott.......

Thanks very, very much for that link. That is EXACTLY what I was looking for.

Simple, effective and compact.

Thanks again.

Doug

[steveciambrone]

Dan not dense, but it is a bit confusing, C10 is C divided by 10=200ma, I think 3C is noted as 3 x C= 6 amps. I am not that good in math so it may be dependent on if the C is in front or behind the C. 3C is the standard for hobby fast charging, but this was started way back when the best Nicad cell was maybe 500ma which 1.5 amps sounds OK. But with the increased capacity it now sounds excessive at 6 amps. Most chargers are not capable of this which is still OK just charge them at what the charger will deliver.

The cells start to warm at the end of the charge even at 200ma. It is the excess energy discipating out of the pack as heat.

Thanks
Steve

"even at a C10 rate 200ma the cells will still be warm"

Steve,
Sorry I seem so dense, but are you saying C10 is 200ma? The pack is 2Ah, so I thought that C1=2A. Then C3 would be 6A, which sounds really high to me.
Thanks,
Dan