High current car charger for P4P batteries...

[Harleydude]

So far, so good....

I hooked the whole mess up just to see if the charger would run through POST. It did.

Next step was to actually charge a battery. I chose a battery that was till @ 70% capacity so the Boost Converter wouldn't have to work so hard. A voltage drop of more than a volt told me that the Boost Converter WAS working hard.

I monitored the Boost Converter's temperature by touching it occasionally (forgot my IR Temp gun). It got pretty warm right away. Since it's 48° outside, I thought I'd move the whole mess outdoors into a shady area. I used the concrete as a sort of heat sink. This seems to be working well. After 5 minutes, no fire.

After 10 minutes, nothing has blown up.

Because this is a serial charger, I can fully populate it without adding more strain to the Boost Converter.

Next I will try charging a more depleted battery. If the Boost Converter doesn't burn up, I'll come up with some kind of forced air cooling solution. Other than adhesive, I don't see any way of mounting it to a heat sink. I have a whole pile of heat sinks so I may go that direction. I guess we'll see.

D

 

[Nanboh]

Switching power supplies like they use to charge lipo batteries really needs to be full sign wave inverter. Chargers can be damaged over time. I use a Goal Zero Yeti 400.

So far, so good....

I hooked the whole mess up just to see if the charger would run through POST. It did.

View attachment 108458

Next step was to actually charge a battery. I chose a battery that was till @ 70% capacity so the Boost Converter wouldn't have to work so hard. A voltage drop of more than a volt told me that the Boost Converter WAS working hard.

View attachment 108460


I monitored the Boost Converter's temperature by touching it occasionally (forgot my IR Temp gun). It got pretty warm right away. Since it's 48° outside, I thought I'd move the whole mess outdoors into a shady area. I used the concrete as a sort of heat sink. This seems to be working well. After 5 minutes, no fire.

View attachment 108461

After 10 minutes, nothing has blown up.

Because this is a serial charger, I can fully populate it without adding more strain to the Boost Converter.

Next I will try charging a more depleted battery. If the Boost Converter doesn't burn up, I'll come up with some kind of forced air cooling solution. Other than adhesive, I don't see any way of mounting it to a heat sink. I have a whole pile of heat sinks so I may go that direction. I guess we'll see.

D

 

[Harleydude]

Switching power supplies like they use to charge lipo batteries really needs to be full sign wave inverter. Chargers can be damaged over time. I use a Goal Zero Yeti 400.

DC doesn't have a "sign" [sic] wave.

D

 

[solentlife]

DC doesn't have a "sign" [sic] wave.

D

DC doesn't have a "sign" [sic] wave.

D

True - but a converter from AC will have either a clean or dirty DC wave to it.

Its why quite often gear wont run of cheap inverter / AC-DC adaptor combo's .... basically the adaptor fails to work.

 

[With The Birds]

DC doesn't have a "sign" [sic] wave.

D

Maybe it’s a sigh wave?

In all seriousness boost converters often have a lot of ripple on the output.

If you have no need for mains power remotely other than battery charging I would be tempted to mount a number of ciggie lighter sockets in a suitable enclosure with appropriately sized cable long enough to reach your battery with crocodile clips on the other end. Better still might be to fashion a harness at the battery end with an Anderson plug or similar. An in line fuse close to the battery would be a good idea. This will allow use of multiple car chargers.

The supply your using now is only a short term proposition- if it works at all. You need 17.4V plus some overhead to charge a 4 cell HV LiPO lack.

 

[Harleydude]

True - but a converter from AC will have either a clean or dirty DC wave to it.

Its why quite often gear wont run of cheap inverter / AC-DC adaptor combo's .... basically the adaptor fails to work.

Take a second look at my circuit. The power brick is for testing only. In real world use it will be replaced by a car battery, thereby eliminating ALL AC from the circuit.

D

 

[Harleydude]

Maybe it’s a sigh wave?

In all seriousness boost converters often have a lot of ripple on the output.

If you have no need for mains power remotely other than battery charging I would be tempted to mount a number of ciggie lighter sockets in a suitable enclosure with appropriately sized cable long enough to reach your battery with crocodile clips on the other end. Better still might be to fashion a harness at the battery end with an Anderson plug or similar. An in line fuse close to the battery would be a good idea. This will allow use of multiple car chargers.

The supply your using now is only a short term proposition- if it works at all. You need 17.4V plus some overhead to charge a 4 cell HV LiPO lack.

I thought of that, but cigarette lighter chargers are far too slow for my needs. My personal experience with a Mavic Pro cigarette lighter was not good. It took over 2 hours to charge the battery...for a MAVIC. Forget that.

I've already spec'd out a 100w boost converter and am going to test that next. My plan is to purchase 2 more Unimaxx chargers and mount each one with its own boost converter and power circuit. I'll probably throw in some active cooling for warmer months. This way I can charge 3 batteries in series OR parallel, depending on my needs. And up to 9 batteries total in a parallel/series circuit. This way, regardless of how many batteries I have in the charger, it will never draw more than 300 watts (roughly 25 amps), but will PROVIDE that much power should I need it. I can idle the engine if need be. A 1.6 Litre engine consumes roughly 1/6th gallon/hour, so I'm in no danger of running out of gas on any shoot, and it's actually on par economically with the 3,000 watt generator we sometimes use on larger jobs.

I've decided to mount a combination ammeter volt meter to the line side of the boost converters so I know how much current I'm pulling and what my battery voltage is. I'm also going to include an audible warning system that will trigger if the car battery drops below a given voltage. But honestly, because of massive voltage variations, voltage is probably not a good predictor of a dead battery. I'll probably just set up a timer and go with that. We'll see.

I'm using a lot of parts out of my parts bin, so the entire cost for this whole thing will be roughly 70 bux.

Because I'm using barrel connectors, I can exchange one or all of the P4P charging bays for Inspire 1 or Mavic Pro chargers. And because the boost converters are variable, I can change their output voltage depending on the need of the charger.

Essentially, I'm building a power supply. I'm not re-inventing the wheel by building an entire charging circuit. Those things are already built by DJI.

Once done, I'll have an automotive 12VDC battery charger system that should've been invented by DJI years ago, but probably wasn't because they were worried about lawsuits from Americans too foolish to monitor their car battery or have any reasonable use expectations. DJI certainly possesses the engineering savvy to build such a beast. But their own legal department probably advised against it. That's the only reason I can think of why DJI wouldn't have marketed something like this years ago.

So far I have charged 2 batteries successfully without the use of heat sinks or forced cooling. Both batteries were at roughly 70% capacity. So I'm convinced the concept works. Now I just need to build something a little more robust. Should be phun.

D

 

[solentlife]

Take a second look at my circuit. The power brick is for testing only. In real world use it will be replaced by a car battery, thereby eliminating ALL AC from the circuit.

D

I was only commenting because of the other guy ... i should have written better post.

 

[With The Birds]

DC doesn't have a "sign" [sic] wave.

D

You might like to have a look at the output of the boost converter. They are a basic switch mode power supply and often have nasty ripple and harmonics on the output. It isn’t pure DC. Perhaps some decent reservoir caps and/or a series inductor on the output will smooth it out if needed. The lipo cells themselves are probably very tolerant to noise however some of the components in the charge board may not be happy.

 

[Harleydude]

Phase II testing complete...

This evening we charged a fully depleted battery from 0% capacity to 100% capacity.

First, dig up a mess of heat sinks from my scrap pile.

Then wash 'em.

Then remove the old media.

Then do a swell job of taping the boost converter to the heat sink.

Then put the whole mess outside in the cool night air to charge.

Success!! Fully charged!

I have some thermal paste on the way along with some 100w boost converters and mess of other goodies. So far, so good!

D

 

[Harleydude]

Looks like I finally found a boost converter that's going to work.

I have total control over the charging process. Now to order more parts and then build the mutha.

Here she is toward the end of the charge.

Side note: If my NEW calculations are correct, it looks like charging 3 batteries at once is going to take it's toll on my car battery. We're still in the testing phase, but charging one battery @ 100 watts dropped the car battery voltage down to 11.7 VDC. So I can only imagine how hard it's going to be with 3 batteries. Looks like I might have to run my car for anything past 9 or 10 charges. We shall see.

Getting excited... This is a phun project.

D

 

[With The Birds]

Looks like I finally found a boost converter that's going to work.

View attachment 109224

I have total control over the charging process. Now to order more parts and then build the mutha.

Here she is toward the end of the charge.

View attachment 109225

Side note: If my NEW calculations are correct, it looks like charging 3 batteries at once is going to take it's toll on my car battery. We're still in the testing phase, but charging one battery @ 100 watts dropped the car battery voltage down to 11.7 VDC. So I can only imagine how hard it's going to be with 3 batteries. Looks like I might have to run my car for anything past 9 or 10 charges. We shall see.

Getting excited... This is a phun project.

D

You will be lucky if the car starts after charging 4 empty (low SOC) packs. The alternator should deliver enough current at idle to keep you going though.

 

[Harleydude]

You will be lucky if the car starts after charging 4 empty (low SOC) packs. The alternator should deliver enough current at idle to keep you going though.

We'll see. I have engineered into this mess an audible low-voltage warning. I have also spec'd a voltmeter/ammeter into the mess so I can actively monitor TOTAL current draw and voltage drop. Now it's just a matter of testing to figure out a good threshold. As I'm sure you're aware, battery voltage under a load is significantly different from a battery at rest. I'm sure you're also aware that voltage recovers over time. So it's a matter of figuring out how deep the voltage can drop before it reaches a critical point (of no recovery). I'm going to guess I can stress the car battery down to around 11 volts and still recover enough voltage at rest to allow the car to start. I'm going to guess 10.9 is probably the breaking point, but it's a tough call because a 15 amp draw might just take the battery down past 11 volts and still allow for recovery. Conversely, if the battery reaches 11 volts over time with a lower 4 amp load, it might not recover. Some experimenting is in order.

At this point the plan is to sett up 3 chargers with different current limits. I can set up the first charger with a quick 5 Amp charge, and then perhaps 4 amps and 3 amps respectively. I can label them "Fast," "medium" and "slow." We'll see. I can experiment at home where I have a battery charger and a hill to bump start my car if need be. At the very least, the data will be interesting and phun to share.

D

 

[Harleydude]

Hey doods!

Okay...I'm cracking up! TWO battery charges (TB48's from 0%) drained my car battery enough that she would barely start. Not a big deal. When engine idling, there's plenty of available current. My engine goes through roughly 1/6th gallon of gas/hour, so "economy" isn't an issue. So kudos to "With the Birds" who clearly had more realistic car battery expectations.

Theory: I'm going to guess that THIS is why companies like DJI don't make "real" car chargers. Clearly, anyone not in the know could find themselves stuck out in the middle of nowhere with a dead battery. I can imagine how many lawsuits DJI would have to endure from housewives and weekend warriors with their new 107. No worries. Unlike the typical Best Buy drone pilot, I DO have a handle on the battery situation and quite easily know how to negate the inevitability of a dead battery.

D