How big of a charger?

MTVR

Well-known member
Was looking at the Powermax PM3-100-LK 100-amp 12VDC charger. It is compatible with the lithium house batteries that we intend to use.

Their web site says it pulls 15 amps of AC, which is about the max I think I can get away with when feeding it with either a residential outlet or a Honda EU2200i generator.

They make a 120-amp version, but I'm concerned that it would overload the generator or trip a residential breaker. We don't intend to be in campgrounds, so even though we intend to build with a 30-amp shore power input, the actual availability of 30-amp AC shore power is kind of unlikely.

What say ye?
 

Joe917

Explorer
Most quality chargers allow you to set maximum Amps. Check the specs on the unit. Our charger is lithium compatible with a 125 Amp charger, but since we are running lead acid we dial it back to 90 Amps.
 

MTVR

Well-known member
Most quality chargers allow you to set maximum Amps. Check the specs on the unit. Our charger is lithium compatible with a 125 Amp charger, but since we are running lead acid we dial it back to 90 Amps.

Ah, so if I'm tripping a residential breaker or overloading our generator, I can just turn down the charger until the problem goes away?

What charger do you use?

What chargers should we be looking at?
 

john61ct

Adventurer
Was looking at the Powermax PM3-100-LK 100-amp 12VDC charger. It is compatible with the lithium house batteries that we intend to use.

Their web site says it pulls 15 amps of AC, which is about the max I think I can get away with when feeding it with either a residential outlet or a Honda EU2200i generator.
PFC can make a big difference.

I would stick to 100A

Unless you can put a decent ammeter on the bigger one and verify it stays below 90% of the genset peak output.

Note that will also affect genset lifespan, continuous use is better kept below 80%.
 

john61ct

Adventurer
Most quality chargers allow you to set maximum Amps. Check the specs on the unit. Our charger is lithium compatible with a 125 Amp charger, but since we are running lead acid we dial it back to 90 Amps.
Yes that is a pretty rare feature for actual chargers that powerful, please link to your model.
 

dreadlocks

Well-known member
How Big is this Lithium Bank again? Charger Size is gonna be dictated by that.. and with LFP you really wanna charger that has current limiting capabilities, because that bank will take pretty much whatever you give it, healthy or not.

0.4C is typically the target charge rate for LFP, and if you want to leave the table open for increasing bank size down the road probably should have a plan for increasing the charge rate as well if you wish to keep the same recharging times.. so it might also be important to get a charger that can be parallelized to scale with future demands... I wouldn't suggest going any lower than 0.2C or your leaving one of the big advantages of LFP on the table, quick recharging.

You decided 12v is what your bank is running at, not interested in 24/48v bank?
 

MTVR

Well-known member
How Big is this Lithium Bank again? Charger Size is gonna be dictated by that..

We haven't decided yet, but we can afford to go bigger than I was initially planning. I'm thinking at least 400Ah, maybe more.

FWIW, it looks like we can fit no more than about 2kW of solar on the roof, the bigget generator we can fit is also about 2,000 watts, and although we're planning a 30A shore power input, we do not plan on actually having access to 30A power on a regular basis- we might be able to plug into someone's house at times, but we do not plan on hanging out in campgrounds.

with LFP you really wanna charger that has current limiting capabilities, because that bank will take pretty much whatever you give it, healthy or not.

If my charger maxes out at no more than 0.4C, wouldn't I be good to go?

0.4C is typically the target charge rate for LFP, and if you want to leave the table open for increasing bank size down the road probably should have a plan for increasing the charge rate as well if you wish to keep the same recharging times.. so it might also be important to get a charger that can be parallelized to scale with future demands... I wouldn't suggest going any lower than 0.2C or your leaving one of the big advantages of LFP on the table, quick recharging.

Understood.

I'd rather spend the money and do it all as part of the initial build- I don't want to have to do it twice.

You decided 12v is what your bank is running at, not interested in 24/48v bank?

We're using some small 12V winches as part of our plan- I don't know how I would reconcile that with a 24VDC house bank. The winches draw about 20A under no load, so using two of them at the same time would be 40A, and the amperage draw goes up from there under load. We would not be using them a lot, but we would be using them. So for lack of a solution there, and to a lesser extent because the RV market is still very 12V-centric, we're currently planning to configure our house bank at 12V...but I'm all ears...
 

dreadlocks

Well-known member
You should nail down that bank size, a 400AH LFP bank @ 0.4C is 160A, 160A * 12V = 1920W, you could run this through a Honda EU2200 Companion w/30A plug and a 20A circuit on the charger, but that genset is gonna be wound up to 100% load, so you can kiss quietness goodbye.. you do know you can chain Honda EU chargers in parallel if you need more wattage but needa keep a small easy to carry genset.. two together can give yeh 4400W max and each one would be running at half throttle and likely much less decibels.

If your charger maxes out at no more than 0.4C, and can handle continuous duty operation then it would be fine, make sure whatever you get states it works with lithium.. one designed for Lead charging is gonna only expect to output full power for a short time and not hours on end.

No 24V alternative winches? What size Inverter you planning on running? Is your alternator output 12v? I'd of thought those big ass military trucks would be 24v already like most ambulances and stuff with high power needs.. If you double your voltage you cut your amps in half, so things like fuses/cabling and everything goes down.. For smaller 12v loads you can easily convert 24v to 12v with negligible losses with things like these: https://www.amazon.com/Power-Step-Down-Converter-Technology/dp/B003P17X8I?ref_=fsclp_pl_dp_2

Most RV style fridges and appliances are actually dual voltage 12/24v if you check their spec sheets.. if my LFP bank was any larger than it is I'd probably go 24v, its not that restrictive..
 
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MTVR

Well-known member
You should nail down that bank size, a 400AH LFP bank @ 0.4C is 160A, 160A * 12V = 1920W, you could run this through a Honda EU2200 Companion w/30A plug and a 20A circuit on the charger, but that genset is gonna be wound up to 100% load, so you can kiss quietness goodbye..

I don't want to build a system that's running on the ragged edge- I'd rather charge slower and/or downsize the house bank if I need to.

But by your math, I should be able to do the 120A charger off an EU2200i. Do I need the "companion" model to gain the 30A connection, or can I do that off of a regular EU2200i?

...you do know you can chain Honda EU chargers in parallel if you need more wattage but needa keep a small easy to carry genset.. two together can give yeh 4400W max and each one would be running at half throttle and likely much less decibels...

Yeah, but I barely have room for one of them, and the Rube Goldberg factor of running two generators would turn me off.

If your charger maxes out at no more than 0.4C, and can handle continuous duty operation then it would be fine, make sure whatever you get states it works with lithium.. one designed for Lead charging is gonna only expect to output full power for a short time and not hours on end.

Yeah, I'm looking at fan-cooled components, and they say they are designed to work with lithium (although the online operators manual is not real helpful there).

No 24V alternative winches?

Not that I can find. These winches are all going to be working well below their capacity- the smallest winches I could find with automatic load-holding brakes, were rated at 3,500 pounds each.

What size Inverter you planning on running?

The 9K BTU mini-split is rated at about 700 watts, but lists a range that goes up to about 1,250 watts. Here are the specs:

Screenshot_20200717-082035_Drive.jpg

I figured a 2,000-watt fan-cooled pure sine wave inverter would be good.

Is your alternator output 12v? I'd of thought those big ass military trucks would be 24v already like most ambulances and stuff with high power needs.. If you double your voltage you cut your amps in half, so things like fuses/cabling and everything goes down..

It is 24V.

For smaller 12v loads you can easily convert 24v to 12v with negligible losses with things like these: https://www.amazon.com/Power-Step-Down-Converter-Technology/dp/B003P17X8I?ref_=fsclp_pl_dp_2

Yeah, but those winches aren't exactly small loads, even though their use is going to be pretty intermittent.

Most RV style fridges and appliances are actually dual voltage 12/24v if you check their spec sheets.. if my LFP bank was any larger than it is I'd probably go 24v, its not that restrictive..

My wife is looking at the Norcold #N3104 3.7 cubic foot unit. 16.2A @ 12VDC, or 1.8A @ 120VAC. We do not plan to use propane to power it.

And I'm listening...
 
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dreadlocks

Well-known member
16A for that Norcold, oh hell no.. you could run 4 of these Engels with that power envelope: https://engelcoolers.com/collections/powered-fridge-freezers/products/sr70-rv-camping-fridge

LP fridges are made to run off LP or 120VAC primary, the 12VDC is just for driving down the road and they would be the worst possible choice if your not going to actually use LP... get one designed to run off your batteries, you also never have to worry about getting it level so it dont burn up your fridge.. that LP one has to be within a couple degrees of level or its gonna fault and ur food is warm.

If your wiring up a 30A plug, I'd get the companion model.. infact I did, my EU2200 Companion lets me plug my 30A plug right into the trailer without a 15A converter.. so all the wiring is overkill 30A even though the genset cant output much more than 20A.. but its better than running 20A off a 15A plug and finding it welded to your 30A plug later.

If your truck is 24v, I'd be doing a 24v house bank so you can use that big massive engine to charge it up too.. 2kw inverter is about as big as you can get in 12v, beyond that most are 24v.

Its not really rube goldberg to chain gensets together, especially if you have a 30A companion genset.. you simply put another down next to it, plug em together and now your output has doubled.. I'd at least plan to accommodate such a need if 20A power is not enough later on down the road.
 
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john61ct

Adventurer
No. Why little?

Just in general high power loads are often better off with higher voltages.

Even 48V in some cases.

Of course if you **know** those are best for you then stick to a 12V system, simplicity is an advantage too.
 

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