Continue to Site

# Battery power pack to replace AC adapter

Status
Not open for further replies.

#### PKENGLISH

##### New Member
Hi,

I just purchased a wireless microphone system for my camcorder and realized upon arrival that the receiver required an AC adapter. I was wondering if there is a way I could create a battery pack that would power the unit?

Printed on the back of it is "12-18V 160mA"

It's been a very long time since I took a physics class so I wanted to see if someone could help me out with getting this set up correctly and not burning out the transmitter.

Is it 12V-18V AC or DC?
If it is DC then a battery can be used but it takes a lot of battery cells to add up to 12V-18V. The current is too high for just two little 9V alkaline batteries in series. Their total of 18V will drop to 12V in about 2.5 hours.

Thanks for the quick reply, it is DC input... If i could get 2.5 hours out of the battery pack I would be very happy.

The current wireless unit have only gets about an hour on one 9 volt so it would be about the same. I actually just realized that I mistyped and it should be 150mA, not sure if that makes a difference.

Thanks again.

If the unit requires 150mA, then it will consume 0.15A x 2.5h = 0.375Ah during your use.
A lowly Alkaline AAA would do it. You need 12V at the end, so according to the discharge curve, a new one would hold its voltage above 1V for 2.5hours at a discharge current of 0.25A.
So make a battery pack consisting of 12 AAAs.

Thanks for the quick reply, it is DC input... If i could get 2.5 hours out of the battery pack I would be very happy.

The current wireless unit have only gets about an hour on one 9 volt so it would be about the same. I actually just realized that I mistyped and it should be 150mA, not sure if that makes a difference.

Thanks again.
I would probably use two "9V" rechargeable NIMH batteries which are about 250 mA-hr capacity. That would give about 1 2/3 hours run time and reasonable size/cost.

https://www.batteryspace.com/nimhre...hrectangularbattery-ultrahighcapacity1pc.aspx

As for the typical 9V alkaline, I thought their mA-hr capacity was about 500 mA-hr. They would run longer but be very expensive to keep replacing.

Last edited:
The No-Name-Brand 9V Ni-MH batteries are spec'd at 200mAh and at 250mAh.
But Name-Brand Energizer ones are spec'd at 175mAh and at only 35mA and when their voltage has dropped to (the datasheet says 1V but I think it should say 5.6V).
At 160mA it will last only 20 minutes.

Energizer 9V alkaline batteries are rated at 625mAh but only when the current is only 25mA and when their voltage has dropped to only 4.8V.
With a load of 160mA they will last 2.5 hours when the voltage has dropped to 6V for each one.

Thanks for all the help guys, I will give it a try with the 9V and see how long they last. I think i have some NiMH rechargeables laying around so I can give it a go without an investment and always fall back on the Alkaline if need be.

Don't use cheap No-Name-Brand Chinese carbon-zinc batteries from The Dollar Store.
They are almost dead and are leaking before they are sold.

Some of the "house brand" alkalines are pretty worthless too, like the Walgreens brand. I bought a bunch of 9V alkalines and found out they were down to about 8.8V while still in the original pack. maybe sat on the shelf for a long time (?) or just junk to begin with.

The No-Name-Brand 9V Ni-MH batteries are spec'd at 200mAh and at 250mAh.
But Name-Brand Energizer ones are spec'd at 175mAh and at only 35mA and when their voltage has dropped to (the datasheet says 1V but I think it should say 5.6V).
At 160mA it will last only 20 minutes.

Energizer 9V alkaline batteries are rated at 625mAh but only when the current is only 25mA and when their voltage has dropped to only 4.8V.
With a load of 160mA they will last 2.5 hours when the voltage has dropped to 6V for each one.

here is some test data on 9V alkalines discharged at 100mA and 500mA:

https://www.powerstream.com/9V-Alkaline-tests.htm

#### Attachments

• 100mA curve.jpg
69.8 KB · Views: 516
• 500mA curve.jpg
90.1 KB · Views: 441
Last edited:
The No-Name-Brand 9V Ni-MH batteries are spec'd at 200mAh and at 250mAh.
But Name-Brand Energizer ones are spec'd at 175mAh and at only 35mA and when their voltage has dropped to (the datasheet says 1V but I think it should say 5.6V).
At 160mA it will last only 20 minutes.
That surprises me that a NI-MH would lose so much A-HR capacity discharged at around the C rate. This curve from another NI-MH 9V shows more what I would have guessed: at 1C you get 80% of the full rated capacity (200mA-hr). That would mean you could get at least a full hour at 160 mA discharge rate.

#### Attachments

• NI=MH Discharge.jpg
13.8 KB · Views: 546
Last edited:
Here's a generic discharge curve for NIMH that's easier to read:

#### Attachments

• NI-MH curve.jpg
9.9 KB · Views: 1,355
Last edited:
The energizer ni-MH 9v battery is pretty good at low currents but is lousy at higher currents.

You show single cells that do not have the many resistive connections in a 9V battery.

#### Attachments

• 9V Ni-MH battery.PNG
66.3 KB · Views: 792
The energizer ni-MH 9v battery is pretty good at low currents but is lousy at higher currents.

You show single cells that do not have the many resistive connections in a 9V battery.
I see the data, but it still surprises me the battery caves in that badly at such a low discharge rate. The resistive connections should be negligible because the cells are spot welded together at the cases (I take them apart to get little cells for lights). The resistance is non existent at the currents we are looking at. I'll see if I can find any other 9V NI-MH curves, but I didn't see any on first search.

Last edited:
Duracell does not have a datasheet for their 9V Ni-MH battery.
What are they hiding?

OK, curiousity has engulfed me and I tested one of my 9V NI-MH battery.

Battery type: 8.4V @ 160 mA-Hr rated

Brand: Chicago Electric Power Systems (green label)

This is one of the cheapies sold by harbor Freight tools,it's made in China.

TEST METHOD: Attach a 62 Ohm resistor, measure terminal voltage during discharge. At 8.4V, that's a load current of 136 mA. It will be a bit higher or lower as the battery starts at about 9.8V and discharges.

RESULTS:

The battery voltage had it's "flat area" between about 8.0V and 8.2V (stayed there the longest time). The discharge current in this area is about 130 mA ballpark which is 80% of "C" rate.

The battery dropped to just under 8.00V at time marker of 50 minutes.

The battery dropped to just under 7.7V at 60 minutes. That is 1.1V/cell and the typical "end point" for discharge.

I discharged it down to 7.0V (which is 1.0V/cell) and that only increased usage by eight minutes, ie out to 68 minutes total.

CONCLUSION:

I was shocked. If this is a 160mA-hr cell as said on the label, I was discharging it at around 80% of C rate. It delivered about 130mA-hr of capacity when discharged the full 60 minutes down to 7.7V. This means it only lost 20% from the label's rated capacity even though it was discharged at 0.8C. Pretty impressive.

Last edited:
OK, curiousity has engulfed me and I tested one of my 9V NI-MH battery.
Your cheapie Chinese battery is much better than an expensive Energizer one that is made in Germany.

Your cheapie Chinese battery is much better than an expensive Energizer one that is made in Germany.
Have you tested any Energizers? maybe their specs are conservative. The other option (which may be likely) is that the Chinese battery is actually a 250mA-hr battery that they make and sell under different labels with different ratings. I am going to test a "good" 250 mA-hr battery and see what it does next.

I have only 1 Energizer 9V Ni-MH battery but it is bolted inside my Sound Level indicator project. They are too expensive for me to buy one to play with.

MORE DATA:

Battery type: Camelion 9V NI-MH, 250 mA-hr (specs below)

Test method: load resistor of 55 Ohms, terminal voltage measured at 5 minute time intervals.

NOTE: average discharge rate over time was calculated and the mA-hr total over the full 60 minute test is 155 mA-hr.

DATA: (time)batt voltage

(0) 9.53
(5) 9.13
(10) 8.97
(15) 8.87
(20) 8.79
(25) 8.72
(30) 8.62
(35) 8.52
(40) 8.38
(45) 8.20
(50) 7.98
(55) 7.77
(60) 6.98

CONCLUSION: The battery capacity showed a total discharge of 155 mA-hr over a one hour interval. That is about 62% of rated capacity (which is supposed to be 250mA-hr) but it is at the discharge rate of 0.62C which is higher tthan where the rating is made for.

This battery is a little bit better than the one above I tested which was rated for 160 mA-hr, but not a large amount better.

I intentionally chose the 155mA-hr test for this one to match the OP's requirements. This battery would give about one hour operation for that application.

Last edited:
Status
Not open for further replies.

Replies
12
Views
3K
Replies
5
Views
5K
Replies
12
Views
2K
Replies
16
Views
4K
Replies
5
Views
2K