Any ideas for a new power supply

[SkyHiker]

My power supply, a Diehard 750, has worked very well for powering my AVX and Pi. With the Losmandy however apparently I need more power. I found out about that by disconnecting one motor and noticing that the other one started behaving much better. Then I plugged a power cord into the jump starter and suddenly both motors worked better. Must be a lack of power!

I would like to understand why it was not working well enough, and also what the best solution is. If this jump starter can provide 750 Amps then what is the problem powering 2 small steppers? Does the voltage drop the more amps are drawn?

At home it is no problem to plug in a power cord but in the field I would like to have something that works too. What specs should I be looking for if I want another jump starter? I would like to have something that is easily portable, I don't have a whole lot to power, not a laptop just a Pi, EQStar and 2 steppers.

[JayTee]

FWIW, I use 105 Ah deep cycle marine battery from Wally world, $115. It will power everything for a long time. It'll even run my refrigerator. The only problem is it has the density of a neutron star. Yes it's portable but only if you're an Olympic weightlifter.

JT

[KathyNS]

Does the voltage drop the more amps are drawn?

Yes, this is true of all power supplies. The power supply has an effective internal resistance, which you can determine mathematically based on the voltage drop and current.

Are you drawing your power from the car starter output (i.e. the heavy cable with the clamps), or are you drawing it from an auxilliary output? It would not be surprising for the auxilliary output to have more internal resistance, which would give it a larger voltage drop at a lower current.

If it is battery-based, it could be that your battery is getting old. An old battery has a higher internal resistance than a fresh one. Batteries get worn out with use and will eventually not accept a full charge.

[Star Dad]

I don't know about car batteries and low power out length of life. Car batteries are designed for momentary, high power output. Deep cycle batteries are designed for continuous low power output - ie electric trolling motors for fishing boats, camper/RV power. I use Interstate deep cycle batteries and they have lasted about 8-9 years. I tried a Sears brand one but it only lasted about 3 years. But I use them for not just powering my scopes but also to charge my electric lawnmower and snowblower (with a solar panel charger).

I have considered getting a lithium based unit, but almost all that I have heard about are car starters emergency batteries so I'm not sure how well they would perform on low power discharging. I know that many folks here on TSS use these types of batteries.

[SkyHiker]

What about a lithium ion vs. a lead acid jump starter? I saw some discharge curves where the lithium ion remains much flatter than lead acid.

Reading up on deep cycle vs. jump starter I should get a deep cycle but they look like massive square blocks without a cigarette lighter plug, handle and built in charger, which are nice to have. So if I can get by with a jump starter I prefer that.

[Star Dad]

Yeah, I have a cigarette lighter with + and - clamps that I tote along. And my unit weighs in a 60 pounds, I think. It is heavy, which is why I am wondering about the lighter weight Li-ion batteries myself. My current battery is about 3 years old, so it'll last a while yet, but I'm interested as well on what others think of the new batteries. But the best batteries (yet to be mass produced) are carbon-fiber ones. When those finally hit the street they will revolutionize power storage. Electric cars will be feasible, solar/wind power off-the-grid homes will become achievable. It's been about 7 years since I read an article on them that some university had developed. I am told by someone who should know that the manufacturing process is being worked on. But when we will see them on the market is anyone's guess.