How long will a 4.8V 950 mah battery pack last?

[SimonCornes]

I know, how long is a piece of string but I have a pack like this in my DF65 and I'm taking part in an open race next month so if racing starts at 10 and runs until 4.30 I wonder how many packs I'll need? As it happens I have 3 - just in case - but I've not sailed in an Open race this century!! I also wonder how long my Tx pack might last - 9.6v 2000 mAh in a Radiolink AT9S Tx. Worth taking a second set of cells??

Many thanks

 

Simon

[Peter Baldwin]

Hi Simon

I typically can sail for a whole day with one RX battery pack (5 cell AAA) on a DF65 if we are running two or more HMS heats (typically the case with more than 24 boats entered).  I switch off the TX and RX between races to save power if running two heats.  To be on the safe side, change the battery pack at lunchtime (or approximately halfway through racing).  Thus two packs should be sufficient if they are relatively new and not suffering from any form of corosion which can affect the lead resistance and capacity.

For the TX I run a Flysky FSi6 and can run for two days of racing on a set of rechargeable AA's.  One day's racing shouldn't be a problem, but it is always good to have a spare TX battery anyway.  Afraid I  do not have any experience of the Radio link series, but would guess that power consumption is similar.  This applies to most things such as rudder servos, winches RX etc as they can be fine for months and even years and then unfortunately fail when you are at an open meeting, just when you don't want it.  I have known some sailors replace critical items before open events just to minimise the chances of failure.

See you at Blithfield.

Peter

[SimonCornes]

Thanks Pete. I think I’ll sort out an extra 8 Tx batteries then. I have two spare and they seem to come in 6’s ( or is it 4’s???)

Then I’d better read the rules! 

[Peter Baldwin]

From the Radiolink website the spec on the TX battery is:

Industry-standard JST connector makes AT9S Pro is adapt for various battery layouts, 8pcs AA battery, a 2S-4S LiPo or 18650 Lithium battery.  When a TBS Crossfire is connected, the maximum 3S LiPo battery is supported. The new power supply circuit provides longer battery life, 12 hours of fun with a 1800mAh 3S LiPo or 18650 Lithium battery. 

The voltage range is 7.4-18V, so 8xAA Alkaline (12V) or rechargeable (9.6V) will suffice.

Your title had 4.8V (4 cell NiMh) 950mAh for the RX.  Is that the battery you are using or is it a 6V (5cell NiMh) as 4 cell is too in voltage low in my opinion?

[John949]

The Tx pack should life should be very predictable as the current drain is constant.  The spec for your TX should give the current.  You simply divide the mAH rating of the battery by the current to get the time e.g. 1800mAH / 500mA = 3.6 hours.

The Rx pack is more variable.  Although the current drawn by the Rx is constant, the current drawn by the servos depends on the load and is probably more significant than the Rx drain.  In other words you battery will not last as long on a windy day.  If you set the boat up so there is tension on the mainsheet at the fully sheeted in position, this will definitely shorten your battery life.  (Marbleheads with gizmo swing rigs are great battery eaters).

It's best to experiment.  You can tell how much of the capacity you have used by how long it takes to charge i.e. time x current.

Just as a guide, I use a 1300 mAH Lipo with an RMG and that will do 12 (shortish) races in a day and still have plenty left.

[SimonCornes]

1 hour ago, Peter Baldwin said:

From the Radiolink website the spec on the TX battery is:

Industry-standard JST connector makes AT9S Pro is adapt for various battery layouts, 8pcs AA battery, a 2S-4S LiPo or 18650 Lithium battery.  When a TBS Crossfire is connected, the maximum 3S LiPo battery is supported. The new power supply circuit provides longer battery life, 12 hours of fun with a 1800mAh 3S LiPo or 18650 Lithium battery. 

The voltage range is 7.4-18V, so 8xAA Alkaline (12V) or rechargeable (9.6V) will suffice.

Your title had 4.8V (4 cell NiMh) 950mAh for the RX.  Is that the battery you are using or is it a 6V (5cell NiMh) as 4 cell is too in voltage low in my opinion?

It’s a 4 cell pack and the tx shows the voltage at over 5v. I do have a 5 cell pack but have never used it so I don’t know how much quicker the winch might be.

[SimonCornes]

17 minutes ago, John949 said:

The Tx pack should life should be very predictable as the current drain is constant.  The spec for your TX should give the current.  You simply divide the mAH rating of the battery by the current to get the time e.g. 1800mAH / 500mA = 3.6 hours.

The Rx pack is more variable.  Although the current drawn by the Rx is constant, the current drawn by the servos depends on the load and is probably more significant than the Rx drain.  In other words you battery will not last as long on a windy day.  If you set the boat up so there is tension on the mainsheet at the fully sheeted in position, this will definitely shorten your battery life.  (Marbleheads with gizmo swing rigs are great battery eaters).

It's best to experiment.  You can tell how much of the capacity you have used by how long it takes to charge i.e. time x current.

Just as a guide, I use a 1300 mAH Lipo with an RMG and that will do 12 (shortish) races in a day and still have plenty left.

Thanks John, I’m going to have to think about this a bit more ! The racing starts at 10 with last race abandoned by 4.30 so 6 1/2 hours but not switched on all that time. My AA’s are 2000 mah so I’ll take a spare set but I can probably get away with just the one pack switching off between races - unless I’m pinging between fleets if there are two of them!!

[Peter Baldwin]

The spec on the TX is 90mA and so you should get 15 hours and easily 12 from a 2000mAh battery.  2000mAh/90mA is 22, but 12 hours is very conservative and the TX current does not vary with load or distance from the boat. 

Forthe RX, I am guessing that it is 5V when you have just charged it and likely that the actual voltage for most of the day will be between 4.4 and 4.8V.  You will get 20% more speed with a 5 cell pack.  Everyone I know of uses either a 5 cell pack or a 6.6V LiFe rechargeable, but there may be others out there using a 4 cell NiMh unit.

[SimonCornes]

Thanks for that info Pete, maybe I’ll buy another 5 cell 950 NiMh pack then !

[Colin Helliwell]

Whether Tx or Rx, beware of assessing "state of charge" purely on voltage. Here's a discharge curve of a [RC Yachts i.e. Vapextech] 1000mAh LiFe, at a constant 100mA drain (on a SkyRC iMax B6AC). LiPo also falls off the cliff in a similar way; my memory hazy about NiMH but might also be similar.

I know your question was about Tx battery, but for info while I'm here and since you have DF(s): when club sailing my DF95 I use about 25% capacity of a1000mAh Rx battery - 9 till 1 (and maybe switching off for coffee break).

Capacity will drop over time tho - we all get less energetic with age lol - so I occasionally do a full discharge/recharge to check how much oomf it still has.

Personally, I don't bother with rechargeables for Tx. Ok, I only sail 4 hrs a week, but plain 'duracells' [other brands are available] are easy to keep in toolbox/pocket. If your Tx does go flat whilst on the water - and I've been there - they can be changed in 30secs without lengthy drama....

 

Edited March 5 by Colin Helliwell

[SimonCornes]

3 hours ago, Colin Helliwell said:

Whether Tx or Rx, beware of assessing "state of charge" purely on voltage. Here's a discharge curve of a [RC Yachts i.e. Vapextech] 1000mAh LiFe, at a constant 100mA drain (on a SkyRC iMax B6AC). LiPo also falls off the cliff in a similar way; my memory hazy about NiMH but might also be similar.

I know your question was about Tx battery, but for info while I'm here and since you have DF(s): when club sailing my DF95 I use about 25% capacity of a1000mAh Rx battery - 9 till 1 (and maybe switching off for coffee break).

Capacity will drop over time tho - we all get less energetic with age lol - so I occasionally do a full discharge/recharge to check how much oomf it still has.

Personally, I don't bother with rechargeables for Tx. Ok, I only sail 4 hrs a week, but plain 'duracells' [other brands are available] are easy to keep in toolbox/pocket. If your Tx does go flat whilst on the water - and I've been there - they can be changed in 30secs without lengthy drama....

 

Thanks Colin,

I am old fashioned and used NiMh cells. I think they discharge like NiCds, ie maintain their charge for 95% of the discharge cycle then go over the cliff and drop significantly. 
I must say though that I probably don’t need to charge my Tx and Rx batteries quite so often. I had no problems with one Rx and the Tx set I’d charged the night before lasting me all day, and I was switching off in between heats. I was being pessimistic about the performance of the cells because it’s probably safer and also using experience 20 plus years ago when using 800mah NiCds  and a days racing would use 3 Rx packs!  I also had a spare pack of C cells and a Jack socket to plug into my Rx!! Times do change don’t they?!!!

[Colin Helliwell]

13 minutes ago, SimonCornes said:

Thanks Colin,

I am old fashioned and used NiMh cells. I think they discharge like NiCds, ie maintain their charge for 95% of the discharge cycle then go over the cliff and drop significantly. 
I must say though that I probably don’t need to charge my Tx and Rx batteries quite so often. I had no problems with one Rx and the Tx set I’d charged the night before lasting me all day, and I was switching off in between heats. I was being pessimistic about the performance of the cells because it’s probably safer and also using experience 20 plus years ago when using 800mah NiCds  and a days racing would use 3 Rx packs!  I also had a spare pack of C cells and a Jack socket to plug into my Rx!! Times do change don’t they?!!!

Yep, battery chemistries and power densities in particular!

I recommend the IMAX charger - bit fiddly to use manually, tho it has PC and tablet apps too. Does 'all' chemistries, and I like that it'll tell me how much I've used since last full charge - handy to know "great, I still had plenty left at the end of the day". Can be 12v powered too as well as mains.

 

 

[SimonCornes]

40 minutes ago, Colin Helliwell said:

Yep, battery chemistries and power densities in particular!

I recommend the IMAX charger - bit fiddly to use manually, tho it has PC and tablet apps too. Does 'all' chemistries, and I like that it'll tell me how much I've used since last full charge - handy to know "great, I still had plenty left at the end of the day". Can be 12v powered too as well as mains.

 

 

Not come across that charger I must say. I was given a Radient Ascert charger by the guy I bought my DF65 from last year and I’ve used it ever since because it seems to work really well. But then I’m used to using simple  chargers so this one is ‘clever’ in my book but it certainly works and that’s fine right now.