What you look for in a portable power unit

[Btbaker22]

I've been doing a lot of research trying to figure out what will be best for a portable power unit. There are a decent amount of options out there, so I wanted to check in with the community to see what specs are most important to you. In your opinion, what would the optimal power unit look like?

-How many amp hours/ watt hours would it hold?
-How fast should it recharge?
-What are the most important power ports it should have?
-How much wattage output should the 110v power inverter have?
-Is connecting to your smart phone important?
-Should it have an integrated MPPT solar controller?
-Any other features that are important?

Thanks!

 

[john61ct]

Every one of those factors is a personal decision that should be based on the individual use case, ideally with a detailed energy budget based on actual IRL measurement if the load devices and using conservative worst-case numbers.

100-200Ah is a decent range if big fans, PCs or a fridge is involved.

Others will do fine with just 50A - these are at 12V of course.

And personally the way to get the system "right sized" for **your** specific needs, is to cobble it together yourself from known good OTS components.

A side benefit of that approach is much greater value for money.


Inverters should be completely separate, really per load device is best.

Dedicated solar controllers will always be much more efficient than built-in add-on circuitry.

Input rate from shore / genset / alternator inputs should allow a full charge in an hour when needed, depending on that level of power available.

I prefer Anderson connectors myself.

A decent coulomb counting SoC meter is important, in addition to accurate ammeter and voltage of course.

 

[rayra]

so how about divulging some of the info your 'lot of research' has discovered? Or is this just market research for you?

you questions are easier to answer when loads and uses are defined or suggested. Otherwise they are too open-ended. Efficiencies in power conversion impact the size of inverter you want to have. or need.
Is this for a large capacity / RV / extended 'boondocker' or the weekender who can't get their SO to go without promise of electric blanket or AC?
Fast charge infers battery tech that is much more costly than flooded / SLA. Sechsy costs a lot more money.
Price /value is something important you left out, but judging by a lot of ExPo branding and younger customer base, high cost is some sort of virtue apparently.

 

[john61ct]

As soon as "portability" is required, lead batteries are assumed out of the picture.

LFP is really the only chemistry in the running for this niche.

 

[Jman99]

No store brought battery pack/power unit exists thats built for real mens outdoor use, & never will, plain fact. they are all toyz designed to be built as cheap as possible and appeal to the masses with fancy pointless stuff.

if your enquiry is a business/marketing one I laugh as you will never pull it off without spending a fortune and will be stuck making the same old junk.

 

[luthj]

Basic specs-
Must charge in 4 Hours or less from a 120V or 12V source.
Cost- Less than 1.6$ per watt hour.
Capable of running at least 250W 120VAC loads
Capable of supplying at least 40A continuous via DC port
Waterproof USB, 120V, DC ports
Low power display showing SOC and relevant stats (current and voltage).


A bonus would be a built-in DC-DC charger with wide voltage range, and adjustable charge rate.


Personally I can't find anything that meets those specs readily on the web. If I needed one, I would probably take a 40-50AH drop in LFP battery, and build a basic box around it. Could probably get all the necessary functionality that way.

 

[Jman99]

There has to be a legitimate reason for such a unit, for me it's to replace the overland vehicle elctric setup as that is just a mess with many problems. The average person cant possible setup a good vehicle electrical system so put it all in a portable box for them, like a laptop, or portable hot water system.

Here are th eproblems you will encounter:

- LFP smallest size is usually 100AH/group 31. Going custom build pack means big dollars unless it's slapped up like most dropins. You need a battery that is always readidly avaialbe or else you will be stuck when it packs up. Let the dropin makers do all the work.
-All quality parts will be huge, look at a 30A sterling AC charger. No point in a alibaba mppt if you can't get a replacment 6yrs later.
-DC-DC charging is essential and that requires some install on th evehicle unless you mind charging at <10A....
-All chargers, fuses, switches must be readily accessible.
-Trying to wire up such large wire infastructure for at least 50A of charge current is very hard given how little space.
- need internal cooling & vents in warm conds.
-Anything AC & high voltage requires serious build qiality, forget about it if you wanna have it out in the wet conds.
-All portable solar panels are crappy low voltage, well saifery have a high voltage one.
-Battery monitoring requires you know how to capacity test & read voltage properley. But from what I have seen these dropins have accurate SOC and they seem to know the real capacity.
-There is no complete range of chargers from one company, like victron make good SC, but lousy AC chargers.
-how does the unit get mounted in vehcile?

A 125AH LFP full fledge unit will weigh at least 30KG and should be carried like a 'thin' suitcase and able to run 2 50L chest fridges, a quality AC pedastal fan, 2000lumen LED light, few AC cahrgers like phones, flaslights etc. All able to be fast charged off solar & in vehicle driving so each & every time you setup camp you got a full tank.

Answer to Qs:

-As large as youcan possibly make it without the total unit weighing anymore than 30-40KG, you must be able to carry it 20M in one go really.
-at least 0.3C with LFP, going smaller is like putting a 3speed gearbox in a racecar.
-15A ciga connections, 3A USB, few 50A ando plugs. 4 slotpowerboard for multiply AC appliances.
-350W is plenty & a good size, no more is needed as you will drain the battery so quick it will be useless
-Yes but only for setting & monitoring chargers, I have a ramx mount & cheap 80$ phone fo rthis & it works well.
-Only if it's a good one, cheap mppt are a waste of time. Please don't listen to will prowse lol
- multiply solar inputs (up to 4-6 really) that feed the mppt-this means you can hook up alot of small panels spread ovcer the place.

so lite, powerful, fast re-charge. yeah never gonna happen!

 

[67cj5]

Nothing beats the Dometic PLB-40 for ease of use, Speed of Charging and it's Charging options, It can run a 150w inverter, I have plugged a 300w inverter in to it but that was only to use a small wattage Gizmo so I never got anywhere near the 150w recommended limit, And it has a DC to DC Charger built In and it will put out a full 12.8v all the time,

The most power I have ever used from it was 49%,

No they are not cheap but they made it right and did not fill it up with a load of junk you don't need, and they are water resistant,

 

[john61ct]

take a 40-50AH drop in LFP battery, and build a basic box around it. Could probably get all the necessary functionality that way.

Not probably

IMO the only way to go.

For decent LFP, $8+ per Ah @12V ($2 per Ah at per cell level) is a bargain in the US

and that's just the cells, maybe with a cheap BMS

Personally I'd make the "output / monitoring gadget module" a separate box so I could plug into different batteries.

Charging separate again, I'd use a good DCDC that stays with the LFP box, let it be charged from any nominal 12V source, plus an HVC separate from the BMS plus a good dense AC-DC PSU.

 

[Btbaker22]

Thanks for the comments, these are all helpful. Ideally I am looking for a set up in my rig, but after looking a many of the turn key units out there I didn't find one that would specifically have everything I wanted. So I thought I'd build my own, and if successful see if it would meet the needs of others. However I don't know the needs of others, so I thought I'd ask.

Personally I thought user's would want a larger inverter, but it sounds like 500 watt continuous is more than suitable. Correct?
How about portability? Those who own a unit, do you move it out of your vehicle a lot, or primarily use it as a mounted unit?
I like the idea about access to the fuses. Is there any other access you think would be needed?
Ideally I wanted the unit to have the flexibility to DC to DC charge from the truck when running via plug in cable, and have a plugin for solar. Is that sufficient? Overbuilt?

Thanks for the feedback. This is very helpful.

 

[john61ct]

Personally I thought user's would want a larger inverter, but it sounds like 500 watt continuous is more than suitable. Correct?

Again, just silly to ask other people how big an inverter **you** should buy!

Every one of those factors is a personal decision that should be based on the individual use case

Au fond, the answer is **choose for yourself based on what you need**

I have over 15 inverters, each mains-powered device gets put on one appropriate for its needs.

Using a big inverter for a small load wastes a lot of power.

Turn them on and off with the device, ideally wired together so one switch.

Other people think that's whacko, get a big $1500 Magnum for their whole rig full of home appliances and leave it on all the time.

They don't mind running a genset for hours daily, I shoot for mostly-solar use the genny maybe two hours a month even full-timing.

UP TO YOU

there is no one size fits all

 

[john61ct]

How about portability? Those who own a unit, do you move it out of your vehicle a lot, or primarily use it as a mounted unit?

I like portability.

Have designed 1200Ah banks with multiple modular sub-packs so easily moved, for me 35-40lbs is ideal.


> Ideally I wanted the unit to have the flexibility to DC to DC charge from the truck when running via plug in cable, and have a plugin for solar. Is that sufficient?

A DCDC charger can be included in the gadget box that stays with the bank.

Other charge sources can be part of the infrastructure you bring the bank to, e.g. an SC needs to be matched with its panels.

I've seen a portable DC genset made of two HO alternators and a Honda engine running off propane, excellent for many use cases but not what most people would consider "part of" a powerpack.

 

[ATskier]

Don't forget about temperature management for lithium. If its heavy and you need to haul it in and out of your vehicle or warm it up to charge it everytime the temp goes into the 20's, (which is frequently where I live), that is a problem.

 

[Btbaker22]

Good call on the temperature comment. I was thinking it would have the cold weather shut off feature, so it can discharge but not charge in cold weather. Or... would it be more useful to have a heated skin around it? If you like the skin idea, would you like it to come on automatically when it senses it's cold, or have a manual switch for it?

 

[taliv]

My system is 306Ah and I think designed by idiots. I’m about to redo it. I got a large inverter and 99x out of 100 I am just using it to charge a laptop or something and it just wastes a ton of juice. I occasionally need something stronger so the idea of two inverters makes sense to me.

easy to repair would be a major consideration