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Author Topic: High current power supplies  (Read 36752 times)

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Offline PDR

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High current power supplies
« on: April 01, 2012, 18:46:37 PM »
One of the few downsides of being one of god's own electric flyers is that batteries need charging, and whilst there is a plentiful supply of cheap, effective chargers they need high-current DC power to drive them. It is typical of the repressive behaviour of the coalition government that they seize upon this opportunity to further torture model flyers by ensuring that domestic homes are supplied only with low-current AC power, forcing us to find ways to convert it into something more usable. Some chargers come with mains inputs, but they are much more expensive, especially in the larger sizes. A few years ago this wasn't a problem because most electric flight involved small models and small batteries, but these days the kilowatt model is common and 2-3kW ones aren't unusual. These need bigger batteries, which need bigger chargers and much bigger power supplies, and that starts to get rather expensive.

Commercial power supplies are offered through the trade, but they are (IMHO) extremely over-priced and many have poor reliability records (as frequently reported here). A common solution is to use a converted power supply from a desktop computer - I have several of these myself, but they have significant limitations. They usually need loading resistors on the 5v rail to work at all, but the main problem is that they wimp-out at higher currents, often dropping half a volt and delivering very "lumpy" DC. They are also not that reliable because pulling huge currents from the 12v output without putting a similar load on the 5v and 3.3v outputs causes them problems.

There are far better PSUs available - those intended for commercial computer servers. These are far more sophisticated devices, designed to run at full power for months at a time with very high reliability. Those designed to run the vast disk arrays in datacentres have a massive current capacity on the 12v output, and that makes them very suitable for our application. Bought new, they are very expensive. But the tend to out-last the servers they were built for and so there are lots floating around with the computer recyclers as a quick ebay search shows. The only problem with them is usually that they need special interlock connections and signals from the server rack to get them to start up. Getting around these involves messing with mains and high-current DC circuits in a way that's not for the feint-hearted.

I've been tinkering with server supplies for a couple of years with varying success, and I've now found one that can be adapted for our use with no modifications and just some simple external wiring. It is intended for a large HP RAID array and as such has a huge 12v capacity (a whopping 47A) but minimal 5v capacity and no 3.3v output at all, It also has an integral cooling fan, a socket for a standard mains lead. If 47A isn't enough(!) then they have specific provision for connecting in parallel by just connecting a single sensing wire between them.

These units are readily available 2nd-hand for under 20; a computer recycler near me sells them for 15 over-the-counter. The unit in question is the HP DPS-600PB (also known as the "Proliant DL380-G4") 575W server supply:

ila_rendered

At one end it has the mains socket for a standard IEC mainslead (this aslo shows just how small this unit is)

ila_rendered

At the other there are a set of connections.

ila_rendered

The following shows how to make a power supply from one of these. The first thing to attend to is the connections at the end. There are two pairs of high-current blade connectors for the +12v and 0v (or "positive and negative" if you prefer) plus a 3*4 grid of small signal pins. These signal pins can do various things - a couple of them can be used to tweak the output voltage up a bit (about 3/4 of a volt) if you wish, and another couple can slow the fan down to reduce noise. I haven't bothered with either, but the options are there for those who want them. The important signals are the "PSON" (Power Supply On) which is used to remotely switch on a server, and the "PSKill" signal which is an emergency shut-down facility. Both of these need to be connected to ground (0v) to switch on the power supply - if you wanted to have a simple on-off switch you could insert it in these connections. They can be found here:

ila_rendered

You don't even need to do anything clever to make these connections because the pins are a good fit in the contacts used in a standard servo plug. So if you take an old servo plug, pull the contacts out of the plastic housing and cover them with a bit of heatshrink (optional, but very tasty) you just need to then solder all three wires together to make the required lead:

ila_rendered

Again, I covered to soldered joint with heatshrink to keep it neat and tidy. The sockets are just pushed over the required pins like this:

ila_rendered

Now I like to have proper sockets on things, and rummaging through my bits&bobs box I found some old speaker connectors (you can get these from Maplin etc) and then spent a few minutes making an alloy bracket to mount them on:

ila_rendered

This was just stuck on-top of the unit with numberplate tape (like servotape but much, much stronger). I did consider putting the connectors through the side of the PSU but after openning the lid (not recommended) I realised that there just wasn't room and the result could block the flow from the cooling fan. The remainder is a fairly simple wiring job. I prefer crimp connectors in high-current joints, so I used yellow-sized crimps and some 60A motor cable. The only tricky bit was soldering the bared end of the cable into the 12v connector blades - this needs quite a big iron and a lot of solder (remembering the currents going through it). In this case I was running out of wire so I put a U-bend in the end of the wire and soldered it to both blade connectors. At some stage I'll get some more wire and do it properly with four cables rather than two, which will be much easier. I also had to cut the plastic sides of the connector shell to give clearance for the wires, but the result isn't too bad:

ila_rendered ila_rendered

Obviously the proof is in the sachertorte - this was the initial test after confirming the healthy 12.68v at the output:

ila_rendered

After that I added more chargers until I had six chargers each drawing between 5 and 10 amps, and the supply didn't even get warm. I've also tested it driving a 70A ESC in model drawing 51A, and the output was STILL 12.68volts, just like the other server supplies I've tried.

So that's about it - a 47A charger power-supply for under twenty squids, and one that will probably be far more reliable than the rubbish sold through the trade. I commend this solution to the house.

PDR

PS = I mentioned you could parallel these up for more power. You can also stack them in series, but that involves isolating the 0v from the mains earth on one of them, which is what is technically called "dangerous stuff" and needs some expertise to do it safely. I have no intention of giving any advice on that on the basis that it's only a reasonable thing to do if you know what you're doing. There are chaps on RCG who have 2s2p arrays of things like this to give 24v at 100A - I'm fairly sure you could arc-weld using that sort of supply!
« Last Edit: April 01, 2012, 19:30:12 PM by PDR »
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Offline Simon Wood

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Re: High current power supplies
« Reply #1 on: April 01, 2012, 20:14:24 PM »

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Offline Geoff Sleath

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Re: High current power supplies
« Reply #2 on: April 01, 2012, 22:33:52 PM »
Thanks for this, Pete.  Don't blame you for being wary of offering advice for 'dangerous stuff' :)   I do things myself I'd never advise others to do and certainly not in writing and in public.

I've found a source for these on eBay simply by doing a search on the part number you quote.  They are supplied by a place in Farnboror' for 16.99 plus 5.99 postage (I hate these 99p pricings!)  Is that your local supplier?

I worked on ICT main frame computers in the early 60s doing final production testing at GEC.  Power was supplied to the racks along open bus bars along the top and I saw two incidents of people getting badly burned on the low voltage high currents.  One on his fingers because he wore a ring on each hand and the other was through one of those metal expanding bands people used to use to adjust the length of shirt sleeves.  For that reason I have never worn rings - too dangerous.

Geoff


Offline PDR

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Re: High current power supplies
« Reply #3 on: April 01, 2012, 22:49:06 PM »
I've found a source for these on eBay simply by doing a search on the part number you quote.  They are supplied by a place in Farnboror' for 16.99 plus 5.99 postage (I hate these 99p pricings!)  Is that your local supplier?

Yes, that's him. His over-the-counter cash price is a couple of quid less than the Ebay one, and lower still for more than one at a time.

PDR
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Offline Yoyo

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Re: High current power supplies
« Reply #4 on: April 01, 2012, 22:58:06 PM »
I worked on ICT main frame computers in the early 60s doing final production testing at GEC.  Power was supplied to the racks along open bus bars along the top and I saw two incidents of people getting badly burned on the low voltage high currents.  One on his fingers because he wore a ring on each hand and the other was through one of those metal expanding bands people used to use to adjust the length of shirt sleeves.  For that reason I have never worn rings - too dangerous.

Between lathe accidents and one spectacular case of a man nearly getting his finger cauterised off by walking in front of an operating high power radar (he was taking a short cut across the test field, ducked under marked safety ropes and ignored warning lights), I've never worn rings either.

And now I have no reason too anyway  :af :'' :ev
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Offline e-flite_rules

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Re: High current power supplies
« Reply #5 on: April 02, 2012, 08:19:17 AM »
Between lathe accidents and one spectacular case of a man nearly getting his finger cauterised off by walking in front of an operating high power radar (he was taking a short cut across the test field, ducked under marked safety ropes and ignored warning lights)


Jeez!  A cauterised finger could be the least of his problems after doing something as dumb as that!

Offline Yoyo

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High current power supplies
« Reply #6 on: April 02, 2012, 09:48:51 AM »
Jeez!  A cauterised finger could be the least of his problems after doing something as dumb as that!

Darwin in action...
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Offline Sizzling

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Re: High current power supplies
« Reply #7 on: April 02, 2012, 11:33:46 AM »
Thanks for this Pete. This appears to be within my capabilities and would mean I would have a very useful power supply  :af

Offline PDR

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Re: High current power supplies
« Reply #8 on: April 02, 2012, 13:09:14 PM »
Thanks for this Pete. This appears to be within my capabilities

That was kinda why I did the show-and-tell on this one. I've got a number of different server supplies that I've converted over the years, but they have all needed either something a bit different in the logic switching to turn them on or messing with internals on the mains/high-voltage side. This one is superb because you can make it work by just cutting up an old servo plug and connecting wires to the output. You don't need to open the case, add a cooling fan or do anything "clever".

PDR
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Offline spillage

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Re: High current power supplies
« Reply #9 on: April 02, 2012, 16:19:41 PM »
Pete

Many thanks for this post - I have dabbled at making pc supplies from various pc power supplies but never had the knowledge to put it all together - I have a local recycler whom I shall contact and see what he has in stock... my mates who fly 6 cell helis are interested in this too...

Thanks Again

John :af

Offline Yoyo

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Re: High current power supplies
« Reply #10 on: April 02, 2012, 16:45:31 PM »
Many thanks for this post - I have dabbled at making pc supplies from various pc power supplies but never had the knowledge to put it all together - I have a local recycler whom I shall contact and see what he has in stock... my mates who fly 6 cell helis are interested in this too...

That particular server range (the HP DL380-G4) is the Ford Sierra of it's time, there should be millions of them out there.

Pete, server PSUs often have screaming fans - what are these like? I've used loads of those servers but only in rooms with hundreds of other screaming fans going already..
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Offline PDR

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Re: High current power supplies
« Reply #11 on: April 02, 2012, 16:55:00 PM »
The fan on this one is a small, high-revving one that certainly isn't silent. But when I was testing it I had it charging a couple of batteries on one sofa while I was sitting perhaps 10 feet away on the other watching Hornblower and I can't say it was intrusive. If noise really is a problem it can be reduced by putting a thermister (or just a 1k pot) across two of the signal pins (the ones either side of the PSKill line IIRC) - put the thermister in the fan exhaust ant it will be varying with the cooling air exhaust temp. I played briefly with this - if people are interested then I'll work out the details and add them to the thread.

PDR
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Re: High current power supplies
« Reply #12 on: April 02, 2012, 18:33:01 PM »
I've just bought one for 12.95 + 5.95p&p on ebay. I need a decent 12v supply and this fits the bill nicely.
Cheers Pete :af

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Offline Alan

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Re: High current power supplies
« Reply #13 on: April 02, 2012, 19:49:43 PM »
I've been running mething very similar for a while now, spot on 12.03v output at silly output currents, enough to run a pair of 200W chargers charging a 6S 5000mAh pack at 5A plus 3 x 3S 2100mAh packs at 2A, all at the same time!

Mine was a copy of somethig published here , by Peevie I think..
I dunno...

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Offline spillage

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Re: High current power supplies
« Reply #14 on: April 03, 2012, 10:49:08 AM »
phoned my local suppliers of stuff recycled after looking on fleabay... you know do the good thing... forty pounds sir... me think not fleabay here I come!! quoted price on ebay... he said he sells them on ebay for that price... good luck to him...

John ;D

Offline PDR

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Re: High current power supplies
« Reply #15 on: April 03, 2012, 10:55:30 AM »
My local supplier trades as "FarboroughIT" on ebay, and his standard price there is something like 17+p&p. He's cheaper if you turn up in person with cash, and might be cheaper if you phoned him direct rather than trading through ebay (his number is on his ebay shop website).

PDR
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High current power supplies
« Reply #16 on: April 03, 2012, 13:57:24 PM »
My local supplier trades as "FarboroughIT" on ebay, and his standard price there is something like 17+p&p. He's cheaper if you turn up in person with cash, and might be cheaper if you phoned him direct rather than trading through ebay (his number is on his ebay shop website).

Hmm... FarnboroughIT. You haven't recently bought a pallet of old HP server spares have you, Mr Pete from Farnborough?

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Offline PDR

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Re: High current power supplies
« Reply #17 on: April 03, 2012, 14:08:29 PM »
I wish!

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Offline Geoff Sleath

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Re: High current power supplies
« Reply #18 on: April 03, 2012, 22:55:24 PM »
I've just bought one for 12.95 + 5.95p&p on ebay. I need a decent 12v supply and this fits the bill nicely.
Cheers Pete :af

Gerry

Me too, probably from the same source in Kent IIRC.  Pete should claim some commission for the sales :)

Geoff

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Re: High current power supplies
« Reply #19 on: April 05, 2012, 10:00:23 AM »
wow - quick look on fleabay like you do 8.95 delivered - yeah baby!!! :af :af :af :af :af

John

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Re: High current power supplies
« Reply #20 on: April 05, 2012, 19:55:06 PM »
I copied Gerry, mine should arrive soon.

Good "heads up" Peter.
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Re: High current power supplies
« Reply #21 on: April 05, 2012, 20:23:23 PM »
I recieved mine today, It fired up first time no problem at all. i also bought eight pairs of banana plugs and 4mm sockets to make an array of sockets with. I'm going to use some large core twin and earth cables for the power bus. I just need to fabricate the brackets for the sockets.

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Re: High current power supplies
« Reply #22 on: April 05, 2012, 21:03:24 PM »
I recieved mine today, It fired up first time no problem at all. i also bought eight pairs of banana plugs and 4mm sockets to make an array of sockets with. I'm going to use some large core twin and earth cables for the power bus. I just need to fabricate the brackets for the sockets.

Gerry


So did mine with similar success using Pete's suggested links.  I tried to find data on what each of the pins is on that 3 x 4 array with no success, though there is an extensive thread on RCGroups.com on the subject of using server power supplies for battery charger feeds (http://www.rcgroups.com/forums/showthread.php?t=1005309).

I checked the pins on mine for continuity to 0v and voltage (both enabled and not).  The 3 pins at the top are linked together and supply the +5v whenever the mains is on.  There's a -12v source on the middle pin on row 2.  There's a couple of pins that measure roughly +12v but aren't connected together.  Apparently the power supply is capable of sourcing 5v at 7 amps which isn't an insignificant amount.

I checked my 12 volts with a 1.2 ohm resistor and it made that glow bright red without coughing :) so I guess it's OK.  I don't find the fan too intrusive even when I have my hearing aids fitted.

Geoff


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Re: High current power supplies
« Reply #23 on: April 05, 2012, 22:13:31 PM »
Of the other pins one is the "current sense" pin which will synchronise current between parallel'd supplies. Another is a voltage tuning pin that can take the output up to about 14v (but the internal over-voltage protection with shut it down at about 13.7v) and another one controls the fan speed. I've got the full pin-outs somewhere, but the rest don't to anything useful. If you want them I'll give you the pin references for the above ones.

PDR
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Re: High current power supplies
« Reply #24 on: April 06, 2012, 11:25:16 AM »
It would be at least interesting and even useful to know what the the other pins do.  Any extra data would be gratefully received.

I'm going to put my power supply in a box with adequate ventilation.  I have a 40 amp panel meter and I'll put a few big terminals to take 3 chargers.

Geoff


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Re: High current power supplies
« Reply #25 on: April 06, 2012, 21:59:03 PM »

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Re: High current power supplies
« Reply #26 on: April 07, 2012, 13:07:44 PM »
Unit arrived today, works very well. The little pins and jumper "plug" may be fragile so take care to protect them from getting bumped or pulled side ways. The connector plugs "sockets" are likely to need just a little squeeze to give the a firm grip.

Welll worth it.

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Re: High current power supplies
« Reply #27 on: April 07, 2012, 14:17:18 PM »
Does anyone know if the corresponding rack, (fixed), power connector is available??


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Re: High current power supplies
« Reply #28 on: April 07, 2012, 14:52:12 PM »
...There's a -12v source on the middle pin on row 2...

That could be useful for getting 24v out for foam cutting  :af

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Re: High current power supplies
« Reply #29 on: April 07, 2012, 19:05:12 PM »
That could be useful for getting 24v out for foam cutting  :af

I think that it's only low power - 0.75 amps IIRC.

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Re: High current power supplies
« Reply #30 on: April 07, 2012, 19:31:37 PM »
Is that so?  The converted ATX power supply I'm using can supply about 8A on that setting - more than enough to power a 1M bow  :-\

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Re: High current power supplies
« Reply #31 on: April 07, 2012, 21:34:42 PM »
Is that so?  The converted ATX power supply I'm using can supply about 8A on that setting - more than enough to power a 1M bow  :-\


I can only assume the description "middle pin on row 2" relates to one of the control signal pins as identified in PDR's pic at the start of the thread;



I can't see any of those pins supplying more than perhaps a few hundred milliamps. $%&
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Re: High current power supplies
« Reply #32 on: April 07, 2012, 22:49:35 PM »
I can't see any of those pins supplying more than perhaps a few hundred milliamps.

You're right, 500 of them according to the label (courtesy of RCG). So for a 24V supply exceeding this you'd need to series connect two of them. Examples on RCG and a couple of other places to help.

ila_rendered

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Re: High current power supplies
« Reply #33 on: April 08, 2012, 00:15:40 AM »
Anyone know what the mating connector in the server box looks like for the high current 0 & 12v connections?  I'd prefer to use a connector rather than soldering to the "pins" on the PS.  Probably as much as a comment on my (lack of) soldering skills as anything else!




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Re: High current power supplies
« Reply #34 on: April 08, 2012, 08:38:57 AM »
Anyone know what the mating connector in the server box looks like for the high current 0 & 12v connections?  I'd prefer to use a connector rather than soldering to the "pins" on the PS.  Probably as much as a comment on my (lack of) soldering skills as anything else!


I found spade connectors fit very well and you just need to crimp them. Ones I have are similar to these http://www.halfords.com/webapp/wcs/stores/servlet/product_storeId_10001_catalogId_10151_productId_160811_langId_-1_categoryId_255229

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Re: High current power supplies
« Reply #35 on: April 08, 2012, 09:12:25 AM »
They will, but you'll struggle to get over 40Amps through a spade connector.

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Re: High current power supplies
« Reply #36 on: April 08, 2012, 09:33:23 AM »
They will, but you'll struggle to get over 40Amps through a spade connector.

PDR

You can get two on both positive and negative terminals. I might have to be a little clever in how I wire them to that distribution box above but I'm sure it will be good enough for my uses. This thread is causing me expense, I'm now considering a 4x100w charger for the 2m Sebart Sukhoi all because I now have power to charge it  :D

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Re: High current power supplies
« Reply #37 on: April 08, 2012, 10:51:02 AM »
Hi,

What AWG wire can you get into the yellow series crimp connectors?

Ta

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Re: High current power supplies
« Reply #38 on: April 08, 2012, 11:11:36 AM »
What AWG wire can you get into the yellow series crimp connectors?

10-12AWG  Yellow
14-16AWG  Blue
16-22AWG  Red

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Re: High current power supplies
« Reply #39 on: April 08, 2012, 15:55:24 PM »
You're right, 500 of them according to the label (courtesy of RCG). So for a 24V supply exceeding this you'd need to series connect two of them. Examples on RCG and a couple of other places to help.

(Attachment Link)

I don't think it works quite like that.  The ATX PS I'm using also has nominal current on the -12x rail, but when bridged across the +12v rail, you get 24(ish) volts, but not quite as many amps as you get on +12v alone - but enough to generate sufficient heat in a 1M long bow.



 

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