Trickle charging an ipad via a truck battery

Thread Starter

chrischrischris

Joined Feb 18, 2012
313
Can someone please help me here.
At our station, we've had a firefighter install an ipad and connected it up to charge as the truck is on. On the ipad, he's setup an autostart app that opens our official CFA paging, mapping and verbal instructions (via google maps) on the route to drive. It's works really well. The only issue he is having is keeping the ipad charged when the truck is off. I'm worried about connecting it permanently whilst the ignition is off.

I've found to charge an ipad when flat is 2amps at 5V DC (10W).
Trickle charge once charged and in sleep mode - no idea - but that's what I'm looking at
Batteries on the trucks - two 12V batteries in series (CCA 650, RC 140, 75Ah).

I feel the battery would loose charge standing idle more that it would trickle charging. Can anyone please confirm.
 

Ya’akov

Joined Jan 27, 2019
5,660
There is no trickle charging for an iPad. It uses a LiPo battery which would be damaged by trickle charging so the iPad's battery management system stops the charging when it is 100% and will not initiate the charging unless it is >90%.

What is the longest time the truck will be off between uses? Is the iPad operated when the truck is off?

Right now, I am leaning towards the suggestion that you get a largish powerbank that supports passthrough charging and connect it to a source that only operates when the truck's accessory power is active.
 
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Lo_volt

Joined Apr 3, 2014
267
@Bob, it's probably still running the app while the truck is off. Given that down time on a fire truck can be several days, it's not inconceivable that it might deplete the battery.

The local fire department in my home town keeps the air brakes on the fire trucks pressurized with a hose to a quick-connect fitting on the truck. It's right near the driver's door so he can pull it as he hops into the truck before he moves. OP, if your fire department does the same would it be possible to put a charger connector near the air hose that the driver can pull at the same time as the air hose? You would need to find a connector that is robust but easy enough to disconnect without slowing down the driver.
 

KeithWalker

Joined Jul 10, 2017
2,354
Is there a radio or any other electronics in the truck that is always connected to the battery to keep its memory alive? If so, that's where to connect the charger.
 

BobTPH

Joined Jun 5, 2013
4,906
@Bob, it's probably still running the app while the truck is off. Given that down time on a fire truck can be several days, it's not inconceivable that it might deplete the battery.

The local fire department in my home town keeps the air brakes on the fire trucks pressurized with a hose to a quick-connect fitting on the truck. It's right near the driver's door so he can pull it as he hops into the truck before he moves. OP, if your fire department does the same would it be possible to put a charger connector near the air hose that the driver can pull at the same time as the air hose? You would need to find a connector that is robust but easy enough to disconnect without slowing down the driver.
You are probably right. It would be a problem if they had to wait for the ipad to boot before they could roll.

Bob
 

LowQCab

Joined Nov 6, 2012
2,049
Is this referring to an actual "Fire-Truck" ?, if so the Batteries are MUCH larger than "75-Ah",
( they're probably closer to ~120-Ah ),
and "draining" the Batteries will not be an issue up to around ~4-days of sitting without being run.

Cranking and Idling the Engine for an hour every other day will keep the Batteries topped-up.

OTOH, if the "Fire-Truck" in question is a Chevy or Ford 2500 Pickup-Truck,
with 2 standard Car-Batteries "in parallel", then a Battery-Maintainer is a great idea.

Actually, a Battery-Maintainer is a good idea either way,
along with a "Block-Heater", ( depending on the Weather where You live ).
.
.
.
 

Thread Starter

chrischrischris

Joined Feb 18, 2012
313
@Yaakov, yes, these are actual fire trucks, and we're a voluntary brigade. The trucks can sit idle for up to 3 days (and rarely 6 days) if there are no turn outs that week. The trucks and pumps are run for around 30 minutes every Wed night and Sunday morning at training. We do aim however to do 30km on each vehicle weekly.

@BobTPH and @Lo_volt, when the trucks are on, yes the ipads keep charged. However, in sleep mode, the apps running in the background will discharge them a bit. We have bought some powerbanks, placed them in the tankers with Velcro, but these too discharge over time as they are not connected to charging in the truck. We can "swap" these over when low, however "other" member won't remember to check their charge and it becomes yet another maintenance issue. And yes, we need to keep the ipad in sleep mode so that it starts up as soon as we press the on button, because it will spell out our route.

Some of the CFA trucks in manned stations are connected to air and power, however ours is not. As a volunteer brigade we can't afford to organise this setup.

@KeithWalker, unfortunately there is no electronics in the trucks to keep memory alive.

@LowQCab, here is the LINK to the batteries. I too was surprised that they are only 75Ah, but that's what the specs say online. There are actually 3 batteries. One delivers 12V to the pump. The other 2 are connected in series to deliver 24V (I assume at 75Ah given they are in series).

Just to add, I rang Century batteries and was told that the batteries we use on our truck are not deep cycle - they are to crank the engine over only.
 
Last edited:

crutschow

Joined Mar 14, 2008
29,792
I would think the trickle-charge current would be too small to have any significant effect on the truck battery charge between uses.
 
I'm using the generic TPS40057 "5V 8A" 4-USB charger board in my car, for my phone and iPad. The boards run to 35V.
Sitting there they use about 0.04A which is not a threat to the truck's battery - assuming the iPad is charged.

What I did is add an input fuse and serious surge protection for 12V SM8A27 (27V 6,600W) typical automotive TVS. Two are used for 24V systems. A firetruck is full of surges due to the high amperage loads switching on and off. A Federal Q-siren is over 12V/100A alone. I'd expect rough power when the truck is running.
I swapped in solid-polymer capacitors because it gets really cold during winter here -30˚C where electrolytic capacitors fizzle out.

It's been working for years with no problems. I know this is a hassle but I wanted something more industrial and what's out there is not so strong and the price of the gear it powers is so high.
 

Thread Starter

chrischrischris

Joined Feb 18, 2012
313
@prairiemystic , if a phone and ipad only draws 0.04A at 12V, does that mean at 24V it would only draw 0.02A? If so, that's nothing.

I like your idea about the PRS40057 USB charger board. However, I'm not sure however why you suggest 2 units for 24V. Reading the specs, it says the input voltage can be between 8V - 35V, so for 24V, a single unit should be good???

I'm happy to put an input fuse as well as surge protector, however can you suggest a suitable voltage suppressor that's not a surface mounted type (i.e. thru hole) - easier for me to put together.
 
Sorry for the confusion - I meant use two 12V surge protectors to make a 24V one. Just one power supply board.
Yes, at 24V the current is half that of 12V for the same amount of power.
An iPad is about a 10W load (5V at 2.1A) while charging. The power supply I suggested always consumes 0.5W load.
Roughly, while charging the iPad current draw is about 1/2A at 24V (12W) and the vehicle battery will be 50% drained in 150hrs or 6 days (assuming they're perfectly new and there is no other parasite drain). The iPad should eventually charge and go to sleep though, it only needs 12W for a couple hours I believe before its battery is full.
As this is mission critical, it might be good to use a charge maintainer for the 24V battery, when the truck is parked. The 12V pump battery must have a special charging system of its own. It could not be connected to one of the 24V system (batteries) as that would imbalance the two and cause troubles.
 

Thread Starter

chrischrischris

Joined Feb 18, 2012
313
@prairiemystic , I've just found a small USB voltage/amp meter I have (LINK). I've connected it to a 240V adapter and to my ipad. It reads 5.04V and 0.06 to 0.07A - whilst the ipad is asleep (and fully charged). This equates to 0.35W if I'm correct.

So at 24V, the amps drawn would be 0.35W/24V = 0.015amps (15mA). So with a 75AH battery, does that mean that it would discharge to 50% in (75 / 0.015) = 5,000 hrs or 200 days? Doesn't this mean it would be safe to connect without draining the battery?
 
The truck already has it's own parasite drain from the battery. The ECU, keyless entry, radio etc needs to be considered as well.
So although adding a say 0.85W/35mA drain looks insignificant, it might be on top of a bunch of others and crater the batteries.
The iPad will periodically wake up and housekeep - look for WiFi, Bluetooth, GPS, and Apple, incoming email etc. and use more.
Why not leave the iPad disconnected and let it run off its battery, not the trucks? They will sleep for days I find.

Jaycar also has some 12/24V USB chargers, but I have not tried them.
 
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