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Old 9th September 2013, 08:31 PM   #1
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Default What diodes would you recommend?

Hi,

I'm clueless about such things, so I'm here in the hope someone can help.



This is a photo I took of my HiFiMan HM-801 digital audio player's double-barreled power connector that's attached to a 120VAC-to-9VDC 0.8A switch-mode PSU:

Click the image to open in full size.

Note the voltages and polarities I've measured. This thing uses the barrels of each 3.5mm x 1.35mm connector to provide 9V DC to one circuit, while using the tips of each connector to provide 9V DC to another circuit.

Indeed, the internal Li-Ion battery that comes with the HM-801 has four contacts on it and is actually two separate battery packs inside one package - not serial nor parallel joined - they are independent.

Problem: These internal battery packs cost $80 each, the HM-801 is already out of production, and HiFiMan will likely run out of battery packs, soon.

This next photo shows my hacked-together prototype for an external battery source for dual 9V DC with the goal of handling loads of at least 0.8A:

Click the image to open in full size.

This is only a prototype that I wouldn't bother using in the field, as the battery capacity is too limited. I have not yet tested this cabling with two Anker Astro3 batteries (I have to buy a second one if I decide to go ahead with this):

Click the image to open in full size.

This wouldn't exactly be "portable," but it could be considered "transportable" - for extended play in the absence of AC outlets.

I suspect a single Anker Astro 3 could be used by employing blocking diodes to prevent the two circuits from seeing each other, but my electronics skills are insufficient to select the appropriate diodes. Anyone with mad skills is welcome to chime in!

Thank you!

Mike

Last edited by zilch0md; 9th September 2013 at 10:40 PM.
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Old 10th September 2013, 02:17 AM   #2
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66 views and no replies thus far... Maybe I should rephrase the question. :-)

Can I just connect both pairs of wires directly to one (higher capacity) 9V battery, such that the two loads have both a common ground (-) and a common hot (+) ?

Thanks

Mike
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Old 10th September 2013, 03:43 AM   #3
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Have you taken resistance measurements across the coax power connectors? Separate batteries strongly suggest the supplies are separate, meaning the power cord has four wires, or at least three.
I don't think blocking diodes will work, because internally the supplies are sure to see each other (unless of course the device uses the supplies for different functions, e.g. one for audio, one for display, but that seems highly unlikely).
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Old 10th September 2013, 12:21 PM   #4
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I find your original post difficult to understand. Perhaps others do too.

My best estimate of what you're trying to ask is shown below in italics. Maybe you can use it as a template to rephrase your question in a more succinct form.
OP owns a portable appliance which has two DC-power-input jacks. The appliance's external power supply has two DC-power-output plugs. Each plug provides 9 volts DC according to OP's DVM measurements. OP does not know whether the portable appliance treats these two DC-power-input jacks as the two rails of a 9V bipolar supply.

OP wants to know if there exists a way to use a single 9V battery and a collection of one-or-more diodes, to drive these two DC-power-input jacks. If so, OP solicits suggestions about which diodes to select (and why).
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Old 10th September 2013, 05:30 PM   #5
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Quote:
Originally Posted by sofaspud View Post
Have you taken resistance measurements across the coax power connectors? Separate batteries strongly suggest the supplies are separate, meaning the power cord has four wires, or at least three.
I don't think blocking diodes will work, because internally the supplies are sure to see each other (unless of course the device uses the supplies for different functions, e.g. one for audio, one for display, but that seems highly unlikely).
Thank you for that suggestion, sofaspud.

I haven't tried measuring the resistance across the connectors - only their voltages when the AC adapter is plugged in. What conclusions might I draw if I find infinite resistance between precisely which points of measurement? (Please help me think this through, because I'm not all that bright with this stuff.)

Let me add that the original battery pack, not pictured, has four contacts on it - you can see the four mating contacts inside the empty battery bay of the photograph I provided. A voltmeter shows about 9V at each of two adjacent pairs of contacts on the original battery pack - evidencing that within that one pack, there are actually two, completely separated 9V batteries.

Quote:
Originally Posted by transistormarkj View Post
I find your original post difficult to understand. Perhaps others do too.

My best estimate of what you're trying to ask is shown below in italics. Maybe you can use it as a template to rephrase your question in a more succinct form.
OP owns a portable appliance which has two DC-power-input jacks. The appliance's external power supply has two DC-power-output plugs. Each plug provides 9 volts DC according to OP's DVM measurements. OP does not know whether the portable appliance treats these two DC-power-input jacks as the two rails of a 9V bipolar supply.

OP wants to know if there exists a way to use a single 9V battery and a collection of one-or-more diodes, to drive these two DC-power-input jacks. If so, OP solicits suggestions about which diodes to select (and why).
That's very well written, transistormarkj! Thank you!

I want to add one correction: The external power supply indeed has two DC-power-output plugs, but each plug, in and of itself, does NOT provide 9 volts DC. Instead, the tips of both plugs provide 9VDC to one circuit within the appliance and the barrels of both plugs provide a segregated 9VDC to a second circuit within the appliance. (See my first photo, above.)

With that understanding, yes, I'd like to know if there's a way to use a single 9V battery and a collection of one or more diodes, to drive the two circuits (which together, present a 0.8A load (going by the PSU's rating), and if so, which diodes to select and why?

Again, I know from experimenting with the 9V Alkalines, that I can safely operate the HM-801 having emulated the voltages and polarities shown in my first photo, above. Thus, a safe and sure way to proceed, would be to purchase two 9V LiPo battery banks (i.e. Anker Astro 3) and cable them just as I have the two 9V alkalines.

But I'd like to reduce the size, weight, and cost by using only one Anker Astro 3, instead of two. Is this possible? If so, how should I proceed?

I have to assume the manufacturer has a reason for building a battery pack with two, independent 9V batteries in it - with four contacts, not two (and not three, with a shared ground). Thus, I'm not willing to just "experiment" with powering both circuits from a single, external 9V battery, without doing something to protect the two circuits from "seeing" each other.

By the way, the HM-801's internal battery only provides about 4-hours of play time per charge cycle, and replacement batteries, while still available for this discontinued player, currently sell for $80 each. I can buy an Anker Astro3 for $55 and hopefully enjoy about 40 hours of play time per charge cycle.

Thanks so much for helping me figure this out. I can tell you that this bit of trailblazing stands to make a lot of HM-801 owners very happy, as we are all nervous about the manufacturer discontinuing their $80 internal batteries. We're not looking forward to the day when we will have to operate these $800 portable players on the AC power adapter, exclusively, for inability to find a battery solution. The new, model HM-901, also uses two batteries in one package, but it's a different size, different charger, etc.

Mike
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Old 10th September 2013, 06:21 PM   #6
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Quote:
Originally Posted by zilch0md View Post
I haven't tried measuring the resistance across the connectors - only their voltages when the AC adapter is plugged in. What conclusions might I draw if I find infinite resistance between precisely which points of measurement? (Please help me think this through, because I'm not all that bright with this stuff.)
Measure resistance between each point and the other 3 on the dual power connector. Finding nothing but infinite resistance is probably the worst outcome; that would be the case if the supplies were truly isolated from each other.
If you find a low-resistance measurement, it is possible that point could be used as a shared reference point of the 2 supplies (ie, ground), and that may provide direction for designing a battery replacement.

That is a very unusual power connector. If a 2-wire (single battery) connection was feasible, I think it would have been used OEM.

Also, consider that if changing from a 4-hour use battery to an 80-hour use battery, the battery will also increase in size by roughly 20x (unless the cell technology is radically different, which it isn't here).
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Old 10th September 2013, 07:07 PM   #7
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Quote:
Originally Posted by sofaspud View Post
Measure resistance between each point and the other 3 on the dual power connector. Finding nothing but infinite resistance is probably the worst outcome; that would be the case if the supplies were truly isolated from each other.
If you find a low-resistance measurement, it is possible that point could be used as a shared reference point of the 2 supplies (ie, ground), and that may provide direction for designing a battery replacement.

That is a very unusual power connector. If a 2-wire (single battery) connection was feasible, I think it would have been used OEM.

Also, consider that if changing from a 4-hour use battery to an 80-hour use battery, the battery will also increase in size by roughly 20x (unless the cell technology is radically different, which it isn't here).
Thanks for hanging in there with me, sofaspud!

Should I measure resistance between each point and the other three while the AC adapter is plugged in or not? (I just know this question reveals my ignorance, but I'd rather be embarrassed than sorry for doing something stupid.)

I will start by doing so with no power applied - when I get home this evening.

Also: My 80-hour estimate is based on 20,000 mAh specification for two Anker Astro 3 vs. a wild guess 1000 mAh for the original internal battery. You've encouraged me to go find out - oops! It's a 4000 mAh specification. So... 20,000 / 4,000 = a 5x increase in capacity (if we can trust the specs), using two Anker Astro 3, but only 2.5x, using one.

Thanks again!

Resistance measurements are forthcoming (with no power applied)...

Mike
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Old 10th September 2013, 07:43 PM   #8
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Quote:
Originally Posted by zilch0md View Post
Should I measure resistance between each point and the other three while the AC adapter is plugged in or not? (I just know this question reveals my ignorance, but I'd rather be embarrassed than sorry for doing something stupid.)
Oh my! Resistance measurements are always with power OFF.
I'm not familiar at all with that media player. These replies of mine are to a great extent just me thinking out loud. Continuing along those lines then...
The 800mA rating from the AC adapter seems like a lot. Maybe it is that high only to provide for the recharge function. It may be worthwhile to measure the actual current draw from the battery during playback. (Ask again if unsure how to do this; power must be on for this measurement, so there's a risk to player and meter.)
Although 800mA seems a reasonable match with the 4-hour use from a 4000mAh battery....
I say this because it seems that for (trans)portable use, you find the PP3 9V batteries too small and dual Anker Astro 3 too big. More accurate supply requirements may help find an alternative solution.
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Old 11th September 2013, 03:25 AM   #9
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Hehe! I'm glad I took the cautious, candid path. :-)

OK, here are the resistance measurements between every combination of barrel and tip for the two plugs. Looking at the picture, again...

Click the image to open in full size.

Imagine the four points of measurement in these positions:

(barrel) 1 ------- 2 (tip)


(barrel) 3 ------- 4 (tip)


1 --- 2 : 1.012 KOhms

3 --- 4 : 0.792 KOhms

1 --- 3 : 0.791 KOhms

1 --- 4 : 0.003 Ohms - a short between the (+) of one 9V battery and the (-) of another - which leads me to conjecture they are using 18V for something...

2 --- 3 : 1.800 KOhms

2 --- 4 : 0.960 KOhms

For each measurement, I waited a while for the reading to become steady.

I'm thinking I better not try to power both circuits from a single 9V battery pack, diodes or not, because it looks as if they've put them in series for 18V, just guessing in reaction to the short between 1 and 4. They could have used an 18V AC adatper with one power plug, but didn't, so it looks as if the player has need of at least one 9V source, if not two, and then for a different circuit, it needs 18V.

What do you think?

Thanks very much!

Mike

Last edited by zilch0md; 11th September 2013 at 03:50 AM.
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Old 11th September 2013, 03:56 AM   #10
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I never had much confidence in the single 9V battery solution.
It does appear they are using a bipolar supply. Without further knowledge of the player's internal power supply, I feel all I can do is shoot in the dark.
Referring back to my previous post, 9V + 9V at 800mA seems like an awful lot for a digital player. Is your battery getting old, where the stored charge/run time is noticeably less than when new?
I would measure the current during playback. You may find that a battery half the size of the Anker Astro 3 is all you need. Then using two won't differ much from the original plan.
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