Large Scale Central

Imax B6AC Deluxe Lithium Ion Charger

Does anyone have experience with the Imax B6AC Deluxe Lithium Ion Charger? I believe it shuts itself off automatically once charging has completed. If that is the case I assume it is safe to leave the battery plugged in?

(Repeat of my answer on MLS)

Timmy, that’s not how it works with Lithium batteries - they turn themselves off. Any battery pack you use should have a BMS (Battery Management System) inside - this is a small pcb that monitors the batteries, preventing over/under charge, etc.

Here’s a typical one (I use them when making battery packs.)

The specs for the BMS are typically something like this:

2: Single Cell overcharge protect voltage: 4.23 - 4.28V
3: Single Cell overcharge protect recover voltage: 4.08 - 4.18
4: Overcharge protect delay: 0.5 - 1.5S
5: Single Cell over-discharge protect voltage: 2.72 - 2.88V
6: Single Cell over-discharge rotect recover voltage: 2.9 - 3.1V
7: Overcharge protect current: 60A
8: Over-discharge protect current: 60A
9: Over-discharge protect delay: 0.5 - 1.5S
10:temperature protect: YES
11:disconnect protect: YES
12:shortage protect: YES
13:shortage delay: 100 - 600μS
14:shortage protect recover: YES
15:Charging current: 25A
16:discharging current: 25A
17:charging voltage : 12.6V for 3S , 16.8V for 4S, 21V for 5S BMS board

In plain english, the BMS turns off the pack when they are charged, or discharged, or short-circuited, etc.

That IMAX charger is more suitable for an RC car battery, which usually won’t have a BMS and will need you to connect the balance charge wires as well as the main charge. It will work, but is overkill.

With a battery pack that has the BMS pcb, you can use a simple charger - I use these inexpensive ones:

I also have a Tenergy LiIon charger, as it enables me to charge a single battery or any multiple. The inexpensive one is only a single voltage, for one type of battery pack. Here’s the Tenergy ‘smart’ charger.

Thanks Peter. I replied to your same post on the other site.

I have one of these chargers I purchased from RLD Hobbies. I asked them if it is ok to leave the battery plugged in after the green light comes on indicating that it is charged and they said NO.

I don’t want to have to be constantly monitoring the battery when it is charging to make sure I take it off the charger once it’s charged.

Not exactly correct. That’s how it works with the dumb chargers that have no settings. What Timmy has pictured is a Smart Charger. It has various charge programs for lots of different chemistries. In the default Li Ion mode, Timmy’s charger will detect the number of cells and and stop charging when the battery reaches the programmed target battery voltage. This method is much better for the battery than waiting for the BMS to shut down the charge.

@timmyd I have several of these. They come in various brands but all use the same chip. It’s fine to leave the battery plugged in.

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I responded to Timmy over on MLS, including mentioning that I often leave my charger plugged in and turned on without any adverse effects.

Jon , just for clarity, Timmy’s charger - the pictured one - is not very smart. It only outputs 16.8V for a 4S pack. It does say “Will not over-charge” so maybe it can detect when the battery pack gets to 16.8V, but it may be that the BMS will cut it off before that!

The same is true of the IMAX B6AC. It can be hooked to a balance cable so that it can monitor every battery, but if not, it is at the mercy of the BMS just like a regular ‘smart’ charger.

Let me be clear that I don’t know whether the charger is constantly stopping to check the output voltage of the battery pack, so it can stop when the battery approaches full charge,
OR whether the charger relies on the BMS stopping charge when it hits its upper limit. In the latter case, the BMS might turn the charging off before the charger notices the voltage anyway!

A prior thread here on LSC suggests reading this thread, which does recommend using an IMAX B6AC.

Well, I can’t tell you the IQ of Timmy’s charger, but it is definitely the only type I will use. I won’t risk burning my house down if a BMS board fails to do it’s job. I have 4 similar chargers, two of which have the Tenergy name on them. The third is an “off brand” and works exactly the same as the Tenergy chargers. They have programmable maximum charge time as will as a charge current.

Hi Tim,

Yes I have this charger. It shuts off once the preset values are reached - these can be user defined but has default settings. Safe to leave connected after shutoff. I have a manual if you want to check details but Google will find you one as well.

Not sure how well it plays with the BMS systems that Pete has mentioned.


I use them on packs with BMS. No issue at all.

Hi Neil,

I would love to see the manual. Can you attach as a .pdf?


Hi Tim, PM sent.


Sorry I cannot help myself !

I would suggest doing the charging in a Lithium Charging bag (google it) or do it outside.

I didn’t receive anything Neil.

Hmmm, shows in my sent emails. Will try again.


Ok, so I connected my new 6 Volt Nicad 350 Mah Replacement P5-605 battery pack to my new IMAXB6AC charger. Set the Imax to NiCad 6 Volt and when I try to charge up the battery pack I keep getting a CONNECTION BREAK error message. What does that mean and how do i fix it?

What it means is that the charger doesn’t see a complete circuit - there’s a break somewhere. (My pals charger kept doing that on his batteries. My charger worked fine to charge the same ones.)
All I can suggest is check that your Nicad battery pack is showing 6V or so on your meter. After that, make sure your charger will charge something, like another battery pack.

The battery pack is brand new. I am trying to charge it up for the first time. I think I am checking the battery pack correctly with my multimeter. It is showing -0.02 which i assume means the battery is totally discharged.

The battery pack I am trying to charge is this one. I set the Imax B6AC to NiCad 6V.
NiCad Battery Pack

Try recycling, by toggling the power switch. Has worked for me.

The power switch? On the charger? There is no power switch.

I think this is your problem. A discharged NiCd battery is about 1.0V, and the pack should register 6V ish on the meter when discharged. 0V is an open circuit, or, as the IMax thinks, a broken connection somewhere.

If it’s new, I’d contact the vendor.