Battery capacity testing. Review of DTL150, a $35 battery capacity tester.

[larryb]

I've always liked the idea of being able to do my own battery capacity testing. But I didn't want to pay $2K for the cheapest unit at Aircraft Spruce. I recently found on Ebay that there are a number of inexpensive testers that can be used. I bought the one below for $35.
It's not quite able to perform the test as Concord specifies, but for my purposes it's close enough. Concord specifies using the C1 current, which equals the amp-hour rating of the battery. It's the current that would draw the battery down 100% in 1 hour. Total power during the test for my 24V battery would be 24V * 13A = 312 Watts. The problem is that the tester only has a capacity of 150 Watts. So I'll use a lower draw of 5 amps. That will result in a slightly optimistic capacity reading since the discharge is at a slower rate. 
The unit has an adjustable stop voltage, so the test can be left to run unattended. The test will end when the specified voltage is reached. For the Concord 24 v battery the stop voltage is 20.0.
The cables that come with the unit are not useful. I made a cable with battery clamps. Note that the unit has remote voltage measurement so you can get battery voltage at the battery terminal and it won't be affected by resistance in your cable. This matters at high current. This is why I used 2 conductor wire between the unit and the clamp, one conductor for the load current and one for the voltage measurement. 
The unit has no manual. You scan the QR code in the middle of the fan for an on-line manual. It takes a bit to get the hang of the button sequences. 
I tried it out for the first time last night. The subject battery had been in service for 5 years and sitting on the shelf for 2 years. I replaced it just because it was getting on in years, but I had no way to test it. The test went well, 7.321 Ah. Percentage capacity 7.3/13=56%. I'm going to try a few cycles to see if it recovers at all. 
 
Cheap unit:
DC0-150V Intelligent Electronic Load Discharge Battery Tester 150W 20A DTL150 US | eBay
expensive Concord unit:
BC-6000 Battery Capacity Tester | Aircraft Spruce
 

[EricJ]

Nice.    I bought a similar unit that I just set to half the draw current and double the time to the stop voltage.   My five-year-old Concorde showed >90% capacity this way, which gave me confidence to keep using it.     I had a hard start condition last month on a hot day at a high DA airport, and the battery held up great.

Yours is cheaper and maybe even a little easier to use, but the one linked below worked fine at a constant 16.5A draw.    I also have an expensive Topdon battery reconditioner that has an automated capacity tester in it, but I don't know how it does the analysis.   I used it to recharge the Concorde after the manual capacity test and it reported the same battery capacity that I got doing the manual test, so that was a nice confirmation.

https://www.amazon.com/gp/product/B07XHLTB4G

[0TreeLemur]

Two years ago I built a battery test rig using an electric dryer heating coil, fan, old Mooney shunt, and data logger.  It drew 13 A.   Not spec, but a fun experiment that I don't need to do again. 

[EricJ]

13 minutes ago, 0TreeLemur said:

Two years ago I built a battery test rig using an electric dryer heating coil, fan, old Mooney shunt, and data logger.  It drew 13 A.   Not spec, but a fun experiment that I don't need to do again. 

It used to be common practice to use an old headlight, but these computerized loads hold the load current constant much more accurately to get a more accurate capacity measurement.    A heating coil was probably a good substitute for a headlight. 

[A64Pilot]

There is something called Peukerts law, basically it states that for a lead acid battery the smaller the discharge current the more Amp Hours a battery will give you and it’s not just a small amount.

‘I’m sure that tester will work fine, just know the battery if tested at a lower rate will give more AH output

https://en.wikipedia.org/wiki/Peukert's_law

Often deep discharge batteries AH is rated over a 20 hour time, discharge one in one hour and you get a lot less, if Concorde specifies one hour then I assume their AH rating is rated at one hour. Manufacturers get bigger numbers if the rate at 20 hours, much bigger numbers.

Resistive loads work well enough for government work but their amp draw is constant but as battery voltage drops so does the draw in wattage.

This is a load bank I built for Certification of an aircraft I had to load the Starter / Generator to max load and then measure temps at different conditions, I think the lights were 800W each, (6,400 Watts) so much heat that I had to have the hopper full of water or they would start a fire. Filament light bulbs work pretty good for a load bank, just be wary of the heat.

 

[skykrawler]

I get the impression that load testing a battery reduces its useful life.

GA jets get load tested - but they also are have time based replacement requirements.

[PT20J]

4 hours ago, skykrawler said:

I get the impression that load testing a battery reduces its useful life.

GA jets get load tested - but they also are have time based replacement requirements.

It shouldn't. First of all you don't do it often -- usually annually. Second, you don't leave it deeply discharged but immediately recharge it. It's sitting around for a long time with a low charge level that causes it to sulfate excessively.

[skykrawler]

 

"When working a discharge cycle, a LA battery should be kept at a DOD of less than 50%, ideally no more than 20-40% DOD; a true^[23] LA deep-cycle battery can be taken to a lower DOD (even an occasional 80%), but these greater DOD cycles always impose a longevity price."

https://en.wikipedia.org/wiki/VRLA_battery

[PT20J]

3 hours ago, skykrawler said:

 

"When working a discharge cycle, a LA battery should be kept at a DOD of less than 50%, ideally no more than 20-40% DOD; a true^[23] LA deep-cycle battery can be taken to a lower DOD (even an occasional 80%), but these greater DOD cycles always impose a longevity price."

https://en.wikipedia.org/wiki/VRLA_battery

Sure, but it is a matter of degree. You only do this once a year on a battery that has a useful life of 4-6 years. The degradation due to the test is probably hard to measure and besides, it is the ONLY way to know the true capacity of the battery.

[EricJ]

I did the capacity test on my five-year-old Concorde battery this spring, mostly because people were saying that's about how long they last.   It tested >90% capacity per the Concorde CMM, even considering the lower discharge current used.    I think they'll last a long time if they're reasonably cared for, which may include minimizing deep discharge cycles both in hard starting events as well as capacity tests, and a desulfating minder probably helps a bit, too.   It's probably hard to say what makes any particular battery last or not, but mine seems to be doing better than I expected.    I'll probably skip capacity testing again for a while unless it does something that suggests it may need it.

[A64Pilot]

On 10/13/2023 at 4:38 PM, skykrawler said:

I get the impression that load testing a battery reduces its useful life.

GA jets get load tested - but they also are have time based replacement requirements.

It has to slightly, but Concorde says it doesn’t. I think if recharged at a high rate immediately at the end of the test the damage is negligible. 

Sulphation is what kills lead acid batteries, and sitting at partial state of charge is what most often seriously reduces their life but even if you do everything perfect and keep one on float etc., eventually it will sulphate and “die”, capacity testing tells you of course how far down that slide to death your battery is.

I wish a charger could desulphate a battery, but they are snake oil. Now if you follow Concorde’s instructions and intentionally overcharge a battery then some of the sulphation can be reversed, but if it’s old sulphation built up slowly over time then it’s unlikely to be able to be reversed, Concorde has their own name for it that I forget but the rest of the battery world calls it an equalization charge

https://batteryuniversity.com/article/bu-404-what-is-equalizing-charge

I assume in this conversation we are talking about Concorde’s VR RG SLAB ? Wet Gill’s aren’t worth the effort in my opinion

[larryb]

I've been doing some more testing on two aircraft batteries. 

 

The Concord, mentioned above, has been used for 5 years and then sat on the shelf un-touched for 2 years. I've done several full charge/test cycles, and the battery has recovered quite a bit of capacity. Next test I think I'll fully charge it and let it sit a week, then sit a month, etc. But for now, here are the results. After the 5th cycle it's 11.2 Ah, or 86%. I don't worry about taking life out of the battery with all of these tests because I'll never return it to service. This is just to get an understanding of the battery behavior. 

1. 7.3 Ah
2. 9.5 Ah
3. 10.3 Ah
4. 11.0 Ah
5. 11.2 Ah

I also have a Gill, used for an unknown time and then sat on the bench for 7 years. It was the battery in the plane when I bought it, and I immediately replaced it with the Concord. I only have two tests on this one:

1. 5.4 Ah
2. 5.8 Ah

Larry

[kortopates]

6 hours ago, larryb said:

I don't worry about taking life out of the battery with all of these tests because I'll never return it to service.

Aren't your numbers showing your adding life to the battery by increasing capacity? Or is capacity of the battery independent of battery life? I assumed more capacity = more life?

[Pinecone]

Sort of.  What I suspect is that the deep discharge/fully charged plus are actually reducing sulphation, so yes, bringing life back in the battery.

It will be interesting to see the results of the battery sitting untouched for a period of time.  To see if it will hold the charge.   Sometimes, in an older battery there are whiskers of lead that lead to higher internal discharge rates.

[Pinecone]

Just now, Pinecone said:

Sort of.  What I suspect is that the deep discharge/fully charged plus are actually reducing sulphation, so yes, bringing life back in the battery.  The is what a equalization charge can help with.  That is, driving the battery above fully charge voltage.

It will be interesting to see the results of the battery sitting untouched for a period of time.  To see if it will hold the charge.   Sometimes, in an older battery there are whiskers of lead that lead to higher internal discharge rates.

 

[Fly Boomer]

11 hours ago, larryb said:

I've been doing some more testing on two aircraft batteries. 

 

The Concord, mentioned above, has been used for 5 years and then sat on the shelf un-touched for 2 years. I've done several full charge/test cycles, and the battery has recovered quite a bit of capacity. Next test I think I'll fully charge it and let it sit a week, then sit a month, etc. But for now, here are the results. After the 5th cycle it's 11.2 Ah, or 86%. I don't worry about taking life out of the battery with all of these tests because I'll never return it to service. This is just to get an understanding of the battery behavior. 

1. 7.3 Ah
2. 9.5 Ah
3. 10.3 Ah
4. 11.0 Ah
5. 11.2 Ah

I also have a Gill, used for an unknown time and then sat on the bench for 7 years. It was the battery in the plane when I bought it, and I immediately replaced it with the Concord. I only have two tests on this one:

1. 5.4 Ah
2. 5.8 Ah

Larry

Wow!  That is some top-notch sleuthing.  Nice work.

[EricJ]

7 hours ago, kortopates said:

Aren't your numbers showing your adding life to the battery by increasing capacity? Or is capacity of the battery independent of battery life? I assumed more capacity = more life?

Proper reconditioning can restore capacity in a degraded battery.   That's what the reconditioning systems do.   It doesn't always work, but it's nice when it does.

[larryb]

I would normally say battery life and capacity are the same thing. But you could also define life as how long the battery will hold it's charge. I will test this next.

 

I think the data shows that the battery does need to be used. Sitting on the shelf 2 years does cause degradation. Can that degradation be reversed by usage? From a capacity point of view it seems so. But for that capacity to be useful it has to hold the charge for at least a month or two. 

[Fly Boomer]

18 hours ago, larryb said:

I've done several full charge/test cycles, and the battery has recovered quite a bit of capacity.

Are you getting those increasing amp-hour readings from the DTL150 Capacity Tester, or is that a calculation?

Also, what do you use to recharge the battery after each discharge cycle?

[Scottknoll]

I’m just doing this myself as well. I’m having difficulty finding RG24-15 batteries. Hoping to save one that barely failed. I am using this dc power supply:
HYELEC DC Power Supply,50V 6A 150W Switching Regulated Bench Power Supply https://a.co/d/5i0d3DV

Concorde Manual specifies power supply and load requirements based on battery size.

[larryb]

I'm getting those amp-hour readings directly from the tester. I set a 5A current draw, 20V test stopping point, and turn it on. The tester will stop when it hits the programmed stop voltage, and you can directly read the amp-hour readings that it achieved. 
 
I use a variable bench power supply to charge the battery. I set it at 28V and 7A. So it will charge at up to 7A max, and when the current reaches the max it'll switch to a constant 28V and the current will be whatever the battery draws. When it gets down to  < 0.1A I consider it fully charged. 
 

[Fly Boomer]

17 minutes ago, larryb said:

I use a variable bench power supply to charge the battery. I set it at 28V and 7A. So it will charge at up to 7A max, and when the current reaches the max it'll switch to a constant 28V and the current will be whatever the battery draws. When it gets down to  < 0.1A I consider it fully charged. 

I bought a power supply I'm using as a GPU.  I can either set constant voltage or constant current.  I use constant voltage for ground power, but if I tried to use it as a charger on a nearly flat battery (after the capacity test), I suspect the current draw would be too high.  I'm not sure what too high is, but the power supply has no way to control it other than whatever its max is.

[larryb]

The bench supply I have allows you to set both max voltage and current.  It won't exceed either of those parameters. So lets say I'm charging a totally flat battery. I've set the voltage to 28 and the current to 7A. The supply will output whatever voltage required, up to the 28, to achieve that 7 A current. So at the start of the charging cycle that might be 11 or 12 V. Once the current drops below 7A the unit will just output the selected voltage, 28 in this case. The max current on this particular supply is 11A I think. I've been using the lower value just to reduce heat and stress on the unit. It has a fan that comes on when it gets hot.

 

Most all supplies these days are regulated so they will not damage themselves. 

Larry

[EricJ]

25 minutes ago, Fly Boomer said:

I bought a power supply I'm using as a GPU.  I can either set constant voltage or constant current.  I use constant voltage for ground power, but if I tried to use it as a charger on a nearly flat battery (after the capacity test), I suspect the current draw would be too high.  I'm not sure what too high is, but the power supply has no way to control it other than whatever its max is.

That's why you either have to pay close attention to how the battery is being recharged or buy a reconditioner, or at least a smart charger, and Concorde's CMM has pretty detailed instructions for load testing, charging, reconditioning, etc.   Some reconditioners are outrageously expensive, but I was dealing with enough batteries (trucks, race cars, cars, airplanes) that I bought a Topdon Tornado 90000, which is not quite a full reconditioner but has a "smart charging" mode that is pretty close, and a wide enough range of battery handling that it's been useful.    I used one of the electronic loads (like cited in this thread) to measure capacity on my Concorde last spring, and had used the Topdon to pre-charge it and then to recharge it when done.   The Topdon also makes a capacity estimate based on whatever it can measure during its smart charge, I guess, and it matched very closely to what I'd measured with the controlled load.

They're not cheap, around $750-$800 these days apparently, but if you handle a lot of batteries it's the sort of thing that can be considered.    Otherwise a good power supply and some quality time on a bench can get there, too, like previously described.

https://www.topdon.us/products/tornado-90000

https://www.topdon.com/products/Tornado90000     <- Glitzier marketing and a little more info.

[Fly Boomer]

1 hour ago, EricJ said:

They're not cheap, around $750-$800 these days apparently, but if you handle a lot of batteries it's the sort of thing that can be considered.    Otherwise a good power supply and some quality time on a bench can get there, too, like previously described.

I do love my tools, but that's a little steep for one airplane with two batteries -- especially when my IA has a capacity tester he can use on my batteries each annual.  I had been using a 24-volt Concord-specific BatteryMINDer on my batteries (two 12-volt in series), but they didn't pass the capacity test recently, so I bought new ones.  Experiencing significant delays in my "annual inspection" so I'm thinking about getting a 12-volt version of the Concord-specific BatteryMINDer to use on these batteries while they are waiting to go into an airplane.  I think I read that it will go up to 8 amps, but I don't know if that's enough to bring a battery back up after a capacity test discharge.