Connecting battery to HAM power supply issue

[JHZR2]

I have an Astron 20A HAM power supply. Im looking to use it for another purpose, specifically, a supply to support coding of my 135i.

So before I just randomly connected the supply to my car, I wanted to see how it would behave connected to just a battery. So I connected it to a fully charged group 49 AGM, and turned it on. No matter how I set it, or what I do, I keep blowing fuses in the connector.

Ive been trying to just protect the conductor with a 15A fuse, and I suspect that it is not prudent to connect higher than a 20 or 25A fuse given the rating of the power supply. But do I need a pre-charge resistor or something else? Im not sure if the issue is inrush, capacitance in the supply, or what. Polarities are correct.

Id think that setting the supply at, say, 15V, with a current limit of 2-3A, on a battery that is at 12.7V, would appropriately connect and then current limit the charging of the battery. Instead the fuse pops no matter what. Adding consistent resistance in series would provide voltage drop that Im not keen on doing, as it means that Id need to monitor terminal voltage with yet another meter... And Im not sure how all this plays into the scenario of adding some energy to the car when it sits electrically on, engine off, during coding runs.

I may try another scheme, like just put another battery in parallel to keep the car awake and voltage good for coding, but the right way is a constant voltage power supply.

Any thoughts???

 

[Lawn_Care]

Did you use an inline Diode to protect the supply from back-feeding power into it from the battery? Not saying that's an issue, but it's the common practice.

Here is a link that will help you with the project. Some Astron supplies are setup for an inline battery (and charging it), some are not. It's a pretty simple mod for them though.

Here is another that might help.



Hope thess links help you out, man. 73

 

[The_Eric]

Don't know if this is 100% correct, but when I'm scanning/diagnosing a vehicle, many times I'll hook up a regular battery charger and depending on its state of charge I will set the charging amperage to 10 or 40 amps. This will keep koeo voltage to between 12.5 and 14.8 volts, which does what I need.

 

[wrcsixeight]

The AGM battery even fully charged, will accept everything and more than the power supply can provide, briefly.

My AGM, when fully charged, and hooked to my adjustable voltage Meanwell rsp-500-15, which maxes out at 40 amps, even when set for 13.5 volts, will briefly exceed 25 amps in the short time it takes to take the AGM from 13.06v to 13.5v.

If set to 14.4v it will max out at 40 amps, briefly. If the battery is depleted, it maxes out at 40 amps for as long as it takes to get the battery voltage to 14.2 or so, at which point amps begin to taper.

There are very inexpensive adjustable voltage power supplies available on Amazon that have a 12.2v to 15.3v range. One could match the power supply voltage to the battery voltage and not have any inrush when first connected. But hooking a 15v power supply to a 12.7v battery will always max out the power supply, briefly.

Most healthy AGMS do not require much amperage to be held at higher voltages when fully charged , but getting them up there in the first place will cause a huge inrush, and blow fuses on power supplies that were never intended as battery chargers.

 

[JHZR2]

I've not added any inline diodes/resistors/etc, yet. Just an inline fuse. Just wanted to see what happens.

I'm running the experiment to see if when I connect the supply to a point on the 12v bus in the car, what would happen. Thus why I view it as a direct connection to the battery, because when I connect to the car for coding, I would do so by the battery charger cable I have connected to some 12v always hit cables under the hood.

When I started up the power supply, it would blow the fuse even if I had the power supply voltage matched to the battery, and/or the current limit turned down to manage it. All worked fine when connecting to a resistive load.

Thing is I want a constant voltage source which will provide full current up to its capability. for coding,mine is supposed to use a constant voltage source to keep the battery and car up.

 

[Johnny2Bad]

DC Power Supplies, and Automotive batteries for that matter, are not trivial devices. For starters, that 12V AGM battery can discharge more than 200A. It has internal resistance, and requires specific charge current as well as voltage.

If your Device Under Test (DUT) asks for 30 Amps and your supply can only safely supply 10 Amps, do not read that to mean your supply will not valliantly attempt, to the point of Suicide, to deliver that 30 Amps. It most certainly will ... That's the essence of how an electrical fire "works".

Why not connect a 12V battery and a trickle charger to your car for "coding purposes". Automotive engine management is not high current demand stuff ... For the most part keep voltage above an easy-to-maintain minimum, maybe 11V and probably less (otherwise you could not start a vehicle with a weak battery) and you're golden. Try the 7A Yuasa 12v SLA model and any trickle charger suitable for lawnmower types. Will work in-car or out-of-vehicle for programming a megasquirt or other aftermarket ECM.

Just do not try and start the car with it. See Paragraph above.

Or maybe I don't understand exactly what, or why, you are trying to accomplish?

 

[Johnny2Bad]

Originally Posted By: JHZR2
I've not added any inline diodes/resistors/etc, yet. Just an inline fuse. Just wanted to see what happens.

Thing is I want a constant voltage source which will provide full current up to its capability. for coding,mine is supposed to use a constant voltage source to keep the battery and car up.


Power Supplies are designed to either be unregulated (attempts to deliver whatever the load demands) or Regulated.

I think one of the bolded is not what you meant to say?

An Unregulated Supply is handy when you have difficult to predict power load spikes you none-the-less want to supply. Disadvantage is they need to be robust to avoid failure which can include releasing the magic smoke that is the actual form of all electric power ;-)

Regulated Supplies are generally designed to provide a condtant current (amps) or constant voltage (volts). Pick one.

You can have both, mind you ... Just add cubic dollars.

 

[Oldmoparguy1]

Is there a need for a high current regulated PS? I would think that a spare battery with jumper cables would work just fine.

 

[supton]

Used to be, unregulated power supplies had an output which varied according to line voltage and load. Naught but a transformer, diode bridge and output capacitance. So as the line voltage varied, so did output; and when the loss rose in the transformer or the diodes, again the output voltage would drop.

*

Years ago I recall some people would put a battery across their Astrons as a battery backup. It makes sense, the supply is at 13.8V which is what a car alternator is at. I would think the same today. If really worried, use a length of wire to connect the battery, the IR loss will act as a ballast resistor. Won't limit fault current but will prevent overcharge.

What Astron model is this? It has been a while since I looked at mine, pretty sure it has a pot to adjust the output voltage, but not for current overload. If it is an older LM723 based design it should be easy to lower the output current limit by changing the sense resistors, although i could see it liking to pop fuses as the current limit is likely not that fast.

*

I presume because of the ECU being on a simple battery tender/charger is not sufficient? If so, then limiting via a 15A fuse is not a great idea. I actually wonder if this supply is too small, as I do not know what the alternator load is, engine off but all computers on.

 

[Win]

Is it a linear or a switcher Astron?

I have a really old ( 90's) 20 amp fixed voltage linear Astron, that is like Supton states, pass transistors wrapped around an LM723 regulator chip. I've not used it to charge batteries because, as best I recall, there is a quirk in the way the old Astrons were made that pops the regulator chip.

I've built small uninterruptible power supplies, with somewhat more modern regulator chips, and a small sealed lead acid battery floating across the regulator chip output, and they work as expected.

 

[JHZR2]

Originally Posted By: Johnny2Bad
Originally Posted By: JHZR2
I've not added any inline diodes/resistors/etc, yet. Just an inline fuse. Just wanted to see what happens.

Thing is I want a constant voltage source which will provide full current up to its capability. for coding,mine is supposed to use a constant voltage source to keep the battery and car up.


Power Supplies are designed to either be unregulated (attempts to deliver whatever the load demands) or Regulated.

I think one of the bolded is not what you meant to say?

An Unregulated Supply is handy when you have difficult to predict power load spikes you none-the-less want to supply. Disadvantage is they need to be robust to avoid failure which can include releasing the magic smoke that is the actual form of all electric power ;-)

Regulated Supplies are generally designed to provide a condtant current (amps) or constant voltage (volts). Pick one.

You can have both, mind you ... Just add cubic dollars.


This is the sort of thing that is supposed to be used:

http://www.amazon.com/OTC-700A-Supply-Battery-Charger/dp/B009RXXTYU

Quite pricey. Id think the HAM PS could provide decent enough quality power with consistent voltage up to the current rating (or at least half the current rating).

Essentially the key when coding (or perhaps more importantly when flashing) is to maintain the DC bus at a nice constant voltage, which some manufacturers can claim to be as high as 50-70A in some situations with the car off. This cannot be achieved with a car battery in parallel, but could possibly with a high enough trickle charger in parallel with the spare battery in parallel with the main one...

But I was looking to do a few things really...

1) Replace my main battery with a new (AGM, group 49) while keeping everything stored and hot to not lose settings, etc.

2) Have the 13.8V constant bus with the car "on" but engine off, so it is pulling some current for an extended time when being coded.


In the end, yes, I want 13.8V from 0 to max rating of the power supply.

 

[JHZR2]

Originally Posted By: Oldmoparguy1
Is there a need for a high current regulated PS? I would think that a spare battery with jumper cables would work just fine.


Some coding sessions can take a long time, especially if modules are reflashed. In theory, yes, another battery in parallel would help, but apparently for best results, one should keep the car at a constant 13.8V while off...

 

[JHZR2]

Originally Posted By: Win
Is it a linear or a switcher Astron?

I have a really old ( 90's) 20 amp fixed voltage linear Astron, that is like Supton states, pass transistors wrapped around an LM723 regulator chip. I've not used it to charge batteries because, as best I recall, there is a quirk in the way the old Astrons were made that pops the regulator chip.

I've built small uninterruptible power supplies, with somewhat more modern regulator chips, and a small sealed lead acid battery floating across the regulator chip output, and they work as expected.



Its a linear Astron, VS-20ML. Has a current limit and a variable voltage output.

My intent was to just see what the behavior would be when I connected the Astron to a battery, so to something that actually has some potential, as this would be the analog of if I were to connect it to my car. Similar to how one would use the (correct) OTC unit seen here:

http://www.amazon.com/OTC-700A-Supply-Battery-Charger/dp/B009RXXTYU

But I figured that before I did anything that involved my car, Id try it just between the PS and the battery. Sure, there would be no load, which might make a difference/nuances, but at least anything I damaged would be off the car.

But making the connection was not in the cards. Each time the fuse (7.5A and then I tried a 15A) would pop. I wonder if I used a 30A fuse or higher, or an unprotected conductor (e.g. jumper cables) if it would work.

I was really trying to get to the bottom of if there would be a major current flow or how the PS would take being connected to something with potential instead of a pure load. My next try might be taking a set of 10ga jumper cables, cut the end off, crimp some lugs onto them, connect them onto the Astron and then to the battery and see what happens.


In other news, I did just take a battery and connect it in parallel which allowed me to replace my main battery without any loss of settings, and also did just enough for the coding to work, without even a trickle charger being connected. But still, Im now intrigued about essentially using an Astron with settable voltage and current limits as a manual battery charger, and if it can do it...

 

[GiveMeAVowel]

@JHZR2:

What is your call, and are you a regular on the Liberty Net? If not what part of the bands do you hang out on?

 

[Win]

I don't know why it wouldn't, unless there is still just something weird about Astrons and batteries.

I've done it with other regulated supplies, linear and switching, store bought and homemade.

 

[Lawn_Care]

Originally Posted By: GiveMeAVowel
@JHZR2:

What is your call, and are you a regular on the Liberty Net? If not what part of the bands do you hang out on?


3.943 - enough said.