Wireless LED and battery lighting for trucks - advice please

[Jivemaster]

Check to see whether any intended load including computer based lighting drivers will shut down nicely when the power goes off. Many nice 12v devices really don't like 15v charging voltages.

[Barney]

On 5/5/2023 at 3:23 PM, Jivemaster said:

The first problem is to define the necessary load and duration.

Agreed, especially as I'm new to all this type of battery power thing! So bear with me...

Based on a suspected 7.5 W/m tape (RGB/W) and a nominal 10m length (actually 2x 5m) then I'm assuming that a load of 75 W would be reasonable as a max draw (excluding other losses which I assume would be negligible).
Simple equation-ing would suggest a current draw of 75/12 = 6.3A for the 10 m strip as a worst case...

So a 6.3 A/h battery would last about an hour, and a 3.2 A/h about 30mins (assuming full RGB/W power etc and some losses for DMX decoder etc)?

Let's assume I need 10mins at full power per show (at one per day) to make it simple. A 3.2 A/h battery would be sufficient, right? Including a few minutes of rig check, etc.

Does this look right - am I missing something obvious?? Is there a de-rating factor that should be allowed for, or something? Appreciate that batteries lose charge but these would be brand new and only need to accommodate a fairly short run.

Thanks,
Barney

[kgallen]

I’m sure members like Tim with lots of experience of this stuff will correct us but I think you need to at least double your battery Ah.

google lead acid discharge curve. A 3.2Ah battery won’t supply 12V @3.2A for one hour then immediately 0V@0A, the voltage tails off over discharge time. You need to determine what the min voltage is for the correct operation of your device then look on the curves for how much discharge that is and scale your battery size with some margin for non ideal devices. 
 

Edited May 15, 2023 by kgallen

[Jivemaster]

Any form of lead acid battery will have a reasonable cycle life if never discharged below 50%. Which demands doubling the capacity on each truck.

Will there ever be two shows in a day (matinee and evening?) because this will mean a short recharge period.

How many trucks will you need? How many chargers will you have?

[sunray]

I don't know about SLA batteries but flooded cell batteries (Car batteries) are usually quoted at a 40 hour rate. 

IE a 20AH battery will supply 1A for 20 hours, increasing the current will give an increasingly shortened time.

As an example for a carnival float we fitted 72 * 10W 50V bulbs @<15A (sponsored by BT) and using 4 * 40AH batteries the bulbs faded to irrelevant in under 2 hours.

So we had the cat and mouse game of waiting for the judges before switching on, then off again until the float was in the publics view when it usually resulted in an audible 'Wow' or 'Ahh'.

Edited May 15, 2023 by sunray

[Jivemaster]

With a lead battery the capacity rating is usually given at 20 hours. Attempting to calculate that back to 1 hour will be unreliable, a 20 hour rating will be probably quartered by a 1 hour discharge. In an extreme example a standard lead acid UPS will discharge from float full to totally empty in less that three minutes and the battery has a life of three full discharges to empty. Fortunately in the UK a basic UPS is unlikely to be called upon often. 

[sunray]

2 hours ago, sunray said:

I don't know about SLA batteries but flooded cell batteries (Car batteries) are usually quoted at a 40 hour rate. 

IE a 20AH battery will supply 1A for 20 hours, increasing the current will give an increasingly shortened time.

As an example for a carnival float we fitted 72 * 10W 50V bulbs @<15A (sponsored by BT) and using 4 * 40AH batteries the bulbs faded to irrelevant in under 2 hours.

So we had the cat and mouse game of waiting for the judges before switching on, then off again until the float was in the publics view when it usually resulted in an audible 'Wow' or 'Ahh'.

Apologies for my 40 hours typo as Jivemaster has stated it is 20 hours and I'll happily agree the quarter capacity at one hour he mentions

Edited May 15, 2023 by sunray

[Jivemaster]

You need to know what will be on the mobile unit as electrical load, and what the DMX receiver needs as supply. Sometimes the use of AA to D size dry cells is a viable option, for the disposal cost you may save money over buying any lithium batteries with chargers.

 

[Jivemaster]

Are these "trucks" being used at a outdoors winter temperature or in a indoor comfortable temperature? Batteries selected for indoor stage use will fail if subjected to winter temperatures in  an unheated space and use in a "winter parade" setting.

[Barney]

Sorry for being dim (haha).

The trucks will be used inside in a typical theatre, so cold weather shouldn't be an issue.

Load is likely to be 75W max for the LED tape (assuming all on full, which is unlikely). The decoder is a typical basic unit (something like this) which should have minimal power draw (?).

Number of chargers and batteries shouldn't be an issue, so we can plonk in a new full 12V battery per show.

I can get hold of 7.0 Ah batteries so am hoping that would be sufficient for the 10 minutes I need the LEDs on per show (even assuming that all LEDs will be on at 100% for that time.

Hopefully that sounds reasonable, but I don't have the knowledge to be able to work it out with any certainty. I guess the simplest way is to make a mock-up and see if it lasts that long! Apologies, I just can't get my head around how quickly the battery would discharge to say 50% with a 75W load on it. Back to school for me!

 

[Tomo]

No need to apologise, this is more complex than you'd like - and the necessary data isn't generally published so you're always guessing to some extent.

75W at 12VDC is 6.25A, so call it 7A total load all-in.
Ten minutes is 1.17 Amp-hours of consumption.

A "high discharge" or "deep cycle" SLA battery is generally assumed to derate to ~50% capacity when discharged at 1C (eg 7Ah nameplate with 7A draw).
So that kind of 7Ah SLA would derate to ~3.5Ah, you'd be using less than 50% of the capacity and be ok.

However, a "standby" or "high capacity" SLA battery (as found in most UPS) derate a lot further at 1C and die very quickly if discharged below 50%.
With Jivemaster's 1/4 estimate, your 1.17Ah @ 7A discharge would take 2/3 of a "standby" SLA, and probably effectively kill it within a few cycles.

I'd suggest LiFePO4 for this application as they're designed for fast discharge down to 20% nameplate capacity.
Most golf carts/electric scooters and "off-grid" systems use them these days as they're cheaper and less ... combustible than lithium polymer.

I believe an 8Ah LiFePO4 is about £50. The chargers are a bit more expensive than SLA, but they also charge faster so you might not need as many batteries.

[Jivemaster]

Look at the whole system as it will get used and abused.

Planning for one cycle per day is easy -how will your system cope with a matinee or just two rehearsals of just the pages where  the trucks are required. Budget for enough chargers and a charging ritual to keep the batteries full. Having someone to control the trucks tightly so that the lights can be switched on and off for the minimum time required. If you've planned for a 10 minute run time and someone lets them run 20 minutes your 7AH battery plan may let you down.

[musht]

Quick comparison on cost and power density.

7Ah SLA 2.05Kg £20 https://www.cef.co.uk/catalogue/products/1287768-7ah-12v-sealed-lead-acid-battery  as mentioned won`t get the full 7Ah out of it

8Ah LFP 862g    £50 https://www.amazon.co.uk/ECO-WORTHY-Rechargeable-Phosphate-Emergency-Fishfinder-8AH-Lithium-Battery/dp/B08ZSBS1ZY even a no name maker is liable to outlive SLA in any frequent drain operation.

8Ah Li Ion 600g  £200 https://tracerpower.com/products/batteries/tracer-12v-8ah-lithium-polymer-battery-pack/ Top end product , can get cheaper , point is the weight difference

 

 

 

Edited May 18, 2023 by musht

[Jivemaster]

Currently your reputation depends on a project that's not been defined yet working to plan for a one week run. You NEED a full and final specification from whoever is doing the truck build. 

Remembering the days of cheap UPS's in the shops reminds me also that the life of the included SLA battery was three minutes per full discharge and three discharges to battery death, simply because the battery was undersized. The show's last night should be it's glittering spectacular finale -the batteries must get that far.

[sunray]

How many trucks are there?

What space is available?

Is there any risk of the truck tipping over?

How many of your people have a caravan containing a leisure battery?