Tracer Batteries & Chargers

[Carbon Brush]

A number of people are starting to use the Tracer lithium battery power packs for powering equipment in the field. These are well made and represent a huge step up from the (Victorian technology) lead acid batteries historically used for astronomy equipment. At about 1/3 the weight for a given capacity, they have to be worth looking into.

The Tracer equipment is well designed and built. It is difficult to damage the batteries (unlike lead acid) though there are still a few considerations that the user needs to bear in mind. This should help to avoid problems that (sometimes unfairly) get blamed on the battery.

The purpose of this thread is to pass on my experience of using a Tracer battery and charger in a non-astro application. The battery was a LiFePO4 module with 40Ah capacity and a buck-boost 12V charger. At around £600 + VAT it is not a choice that most would make for astronomy. Though the precautions and limitations for use are valid across all of the Tracer product range.

The batteries contain a ‘battery management system’ or BMS. This is an electronics package inside the battery and invisible to the user. It provides the following functions:

1/           At a battery temperature of 65C (with +/-5C tolerance) the BMS disconnects power. This prevents charge or discharge when the battery is too hot.

2/           If the battery is short circuited, or subject to a high current overload, the BMS disconnects power. This protects against battery damage and possibly external problems like burning wiring or scope electronics.

3/           If the battery is (all but) fully discharged, the BMS disconnects power. The trip point is about 9V. This prevents battery damage. Though whether yourmount will work down to 9V is a different matter.

 4/          When charging, if the charger voltage rises too high, the BMS disconnects to prevent battery damage. This happens at 14.6V. Note using the BMS in this manner is NOT a substitute for a correct charger being used.

At first sight, the BMS appears to offer comprehensive protection. It is very good but does not cover all eventualities. Consider next the battery temperature limits.

The battery may be discharged (used) from -10C to +60C. Charging is allowed between 0C and +40C.
I have not been given a statement from Tracer about what might happen to the battery if it is used outside of the specified temperature limits.

The BMS disconnects the battery at +65C only. There is no differentiation between charge and discharge. There is no low temperature shut off.

Next is the charger. To the best of my knowledge all the Tracer supplied chargers work over a wide temperature range. They have no way of knowing the battery internal temperature and they do not use any temperature measurement input.

The limitations of the BMS and charger mean that you, the user, need to ensure the battery is not charged or discharged outside of the permitted temperature range. This nothing new. Lead acid batteries and chargers allow considerable battery abuse and often contribute to failures.

So how does this affect you in practice?

On a cold night in the UK you might be using the battery at -10C. Albeit not very often. It is a good idea to start with a warm battery as performance will be a little better and you will have more time before the battery cools. The battery generates no discernible heat in use which means it can be placed in a thermally insulating case.

If using the battery to power a solar scope mount, the temperature may rise due to being in the sun. Again, an insulating box will help slow down heating. Though it is hard to imaging a UK day taking the battery up to 60C – unless it is left in full sun.

Recharging after use presents different issues as the permitted charge temperature range is more restricted. 0C to +40C.

Fortunately, the nature of lithium batteries, and the BMS mean that you do not need to rush to the charger immediately after use. Unlike lead acid, they survive being left discharged for a time.

After a cold night it is a good idea to leave the battery indoors for a time to warm a little before charging.

After a solar session, if the battery feels warm to the touch, do not start charge.

These are simple precautions that will help ensure you get the best possible life out of the expensive batteries.

 

 

[JeremyS]

Thank you for the helpful advice on using these batteries. I have a couple of units: a Lithium polymer and a LiFePO4

[johninderby]

The Tracer LiFeP04 batteries should be stored charged and topped up every six months.

They are a safe design unlike plain lithium batteries that can be dangerous while charging and can self destruct causing fires. They also deliver a “flat” discharge curve and hold their output voltage untill nearly depleted unlike regular gell cell batteries. Only downside to the LiFeP04s is the cost. 

I use then for powering RC tanks as well as astronomy.

Edited August 21, 2019 by johninderby

[Piero]

I have a LifePo4 7Ah. Very happy with it. Mine is used only for turning on the fan of my dobson.

[david_taurus83]

Great little battery packs but you need a large one if powering mount, dew straps, USB hub and tec cooled camera. I had a 12ah one and it would just last me a good nights session.

 

FYI, if you found yourself short and the power indicator was low, you can still use the battery while charging it. I have email confirmation from Tracer that this was ok. You would however be limited by the amp output of the charger.

[michaelmorris]

On 21/08/2019 at 17:36, david_taurus83 said:

Great little battery packs but you need a large one if powering mount, dew straps, USB hub and tec cooled camera. I had a 12ah one and it would just last me a good nights session.

What length of time would you describe as "a good nights session"?

[david_taurus83]

43 minutes ago, michaelmorris said:

What length of time would you describe as "a good nights session"?

5/6 hours. My PSU that I use now has an ammeter and it doesn't go over 2 amps usage so for a 12ah pack 5/6 hours was about right.

[michaelmorris]

23 minutes ago, david_taurus83 said:

5/6 hours. My PSU that I use now has an ammeter and it doesn't go over 2 amps usage so for a 12ah pack 5/6 hours was about right.

Thanks

[Michael Hogan]

I cannot say enough praise about the amazing Tracer 12v 24ah i bought to run my mount Intel NUC8 and ASI294mc Pro ccd for nearly six hours and still be half full

i might buy another Tracer 12v 24ah for running my two dew straps i tested them on the same battery gone five hour and was just under half full these LifePo4

batteries are just insane they just keep running.

Edited September 18, 2019 by Michael Hogan

[garryblueboy]

I use Tracer most of the time the only time I had a problem was with my CPC 11