Maximum C rating ?????

[andy4795]

Having had trouble with the LVC coming on to soon with my 11.1v 5000mah 30c can i use 11.1v 6000mah 45c batteries, or is this going to cause problems with something, please advise, Andy

[dag-nabit]

Having extra C rating won't hurt anything, except maybe your pocket book. Generally speaking the higher the C rating the higher the cost.

Very simplified, the C rating is the ability of the battery to discharge without overheating due to internal resistance.

The battery will still only discharge at the rate demanded by the load.

It is similar to putting a larger pipe on a fuel tank. The tank might be able to drain at a rate of 10 litres a minute, but if the engine attached only uses 2 litres a minute, the tank will drain at 2 litres a minute, unless the load (demand) changes.

If I recall correctly you have 5000mah 30C batteries which can drain at a maximum of 150amps, but if the motor is only calling for say 30 - 60 amps for example, that is all the batteries will supply.

Based on your previous posts, I would be looking for other problem areas before buying more batteries, the 5000 mah batteries you have should be OK in a stock setup Spartan.

Kevin

[filmmaker]

also the higher the C rating the cooler the batteries will run

[dag-nabit]

Hey Andy,

Was mulling over your problem with the LVC cutting in after only a few minutes and had a thought.

Please don't take offense if you have already thought of this and eliminated the possibility.

What type of charger do you have? The reason I ask is chargers range from extremely basic: hook up a battery, plug it in, when the light stops flashing, your battery is charged. These types of chargers are usually tailored to a specific battery type/size.

Higher end lipo chargers require you set the parameters for each type of battery you charge. Cell count, charge volts, charge amps, max charge volts per cell, etc. Some also have a storage charge setting that only charges the battery to 50-60% of full charge.

So I was just wondering if there is a chance your charger may not be set up properly, resulting in your batteries not being fully charged.

Kevin

[andy4795]

Hi Kev cheers for that, my charger is a Fusion LX60B capable of charging life,nimh and lipo batteries to 6A, but will have a look round the settings on it,,,,, Dont suppose you know at what point the LVC should kick in to protect the battery from to much discharge do you ( how many mah in battery ) when it kicked and boat went slow i checked the cells with a meter and each one was reading around 4.1 mah from the 5000 mah 30c batteries i had in. Cheers Andy

[dag-nabit]

Hey Andy,

Each cell on a lipo battery is rated at 3.7 volts nominal. Fully charged they will have 4.2 volts per cell.

3.7 volts x 3s (three cells in series) = 11.1 volts. But fully charged your battery will be putting out 4.2 volts x 3 = 12.6 volts

If you discharge a lipo cell to below 3.0 volts you will damage the cell. A lipo cell that has been discharged to 3.0 volts under load will show approx. 3.5 volts at rest (open circuit).

The LVC is monitoring voltage under load.

So the LVC should never be set lower than 3.0 volts per cell, or 9 volts for a 3S pack (under load).

HOWEVER

With todays high discharge batteries it is very easy for an amp spike to drop cell voltage below 3.0 volts when the pack is nearing full discharge.

Most experienced RC'rs recommend an LVC setting of 3.2 - 3.3 volts per cell (under load) which will give you approx. 3.7 to 3.8 volts per cell at rest (open circuit) or 11.1 - 11.4 volts total for a 3S battery pack when checked open circuit.

Setting the LVC higher at 3.4 or 3.5 volts will protect your batteries even further, but you may find the LVC kicking before the batteries have reached what is still a safe discharge and shorten your run time more than necessary.

I don't know what the LVC is set for in the stock Spartan ESC, It doesn't say in the owners manual.

Here is a link that gives a good elementary education on Lipo batteries http://www.rchelicopterfun.com/rc-lipo-batteries.html

Or google Lipo Battery Info for a ton of info on lipo batteries. Be aware though there are as many opinions as there are articles, so you need to wade through them and find a middle ground you are comfortable with.

So fully charged your battery should show right around 12.6 volts, and after running if you are getting 11.0 - 11.5 volts readings you should be OK. (even down to 10.5 volts but that is pushing your luck IMO)

Kevin

Here is another good link: http://www.rchelisite.com/lipo_battery_charging_and_safety_guide.php
http://sites.google.com/site/tjinguytech/charging-how-tos/the-charging-process

[dag-nabit]

Hi Kev cheers for that, my charger is a Fusion LX60B capable of charging life,nimh and lipo batteries to 6A, but will have a look round the settings on it,,,,, Dont suppose you know at what point the LVC should kick in to protect the battery from to much discharge do you ( how many mah in battery ) when it kicked and boat went slow i checked the cells with a meter and each one was reading around 4.1 mah from the 5000 mah 30c batteries i had in. Cheers Andy


Hi Andy,

Just re-read your post.

That would have been 4.1 volts per cell. Which means your batteries were still close to fully charged.

I think you may have a problem with the LVC in the ESC cutting in too soon, If you are running the stock Spartan ESC I don't know of anyway to check the set point, and I highly doubt it is adjustable.

You may want to contact Traxxas on this one. Might be a warranty issue.

Kevin

[filmmaker]

Hi Kev cheers for that, my charger is a Fusion LX60B capable of charging life,nimh and lipo batteries to 6A, but will have a look round the settings on it,,,,, Dont suppose you know at what point the LVC should kick in to protect the battery from to much discharge do you ( how many mah in battery ) when it kicked and boat went slow i checked the cells with a meter and each one was reading around 4.1 mah from the 5000 mah 30c batteries i had in. Cheers Andy

if your lvc is kicking in and the cells at rest are reading 4.1v the lvc is not working correctly on your esc
have you tried running the esc on the Nimh setting to see if you can run your fully charged packs for longer than a couple minutes without issues?

[andy4795]

Hi there , i did try running my lipos on the nimh setting, ran for 2 mins no problem, i know you should not but needed to try it, cheers Andy

[dag-nabit]

Hi there , i did try running my lipos on the nimh setting, ran for 2 mins no problem, i know you should not but needed to try it, cheers Andy

Definitely sounds like a problem with the LVC. You are correct it isn't a good idea to run without LVC, but you are probably OK for up to 3-4 minutes without worry just to test things out. (sounds like most are getting 6-8 minutes on 5000mah before LVC kicks in)

Kevin