use 52v battery for camping

[Bikegirl]

I'm looking at a compact setup for island camping with a 52V 20ah (14S7P) EM3EV battery I have to charge a 40litre fridge from solar.

My question is will the following setup work? and are my calculations right?

CALCULATIONS
Battery - 52V x 20.7 ah = 1040wh (use 1000wh) (8A max charge current @ 240V, max continuous discharge 40A (HG2 cells))

Brassmonkey 40litre fridge load (running on 12V, real world stats)
uses 3.5A @12V set at 1 degrees, uses 19ah over 7 hours (2.71ah per hr = 65ah per day)
65ah x 12V = 780wh

780wh x 1.2 = 936wh (add 20% for loss from DC conversion and solar charging)

Therefore battery will need a full charge from solar each day to keep the fridge cold

1000wh/150w panel = 6.7hrs of sun required
1000wh/200w panel = 5 hrs of sun required

COMPONENTS
battery $0
$62 400W MPPT solar controller, 18-55V input, 24-85V output
https://www.aliexpress.com/item/100...&terminal_id=5de8a0b6a4764af58aefc2520dabdefc

$39 DCDC converter from 15-60V of battery to 12V 26A 312W supply for fridge
https://www.aliexpress.com/item/400...&terminal_id=5de8a0b6a4764af58aefc2520dabdefc
OR
$62 DCDC converter from 40-90V input to 12V 20A 240W output
https://www.aliexpress.com/item/328...&terminal_id=5de8a0b6a4764af58aefc2520dabdefc

If anyone has tried buck/boost conversion for this purpose i would be keen to know if it works.

Cheers!

 

[Bikegirl]

ALSO

Any comments/recommendations on whether Sunpower Maxeon solar cells are worth it?

I was looking into getting a solar blanket but it needs to be 20v open circuit voltage to be suitqable for the solar controller mentioned

 

[john61ct]

A proper energy budget, in Ah per 24hrs is really the starting point.

Use a coulomb-counting wattmeter to measure the actual Ah used over time - duty cycling between peaks vs low continuous needs to be taken into account.

And don't bother measuring grid power appliances at AC voltage, need to include the inverter overheads.

So say your induction hot plate (as a thirsty example) uses 35Ah over an hour of making soup or spaghetti sauce.

You then guesstimate you'll be using it an average of 40min per day, so ballpark 25Ah/day is your budget for that load device.

Do the same for screen device charging, lights, fans, your fridge etc. until you get a total Ah per 24hrs bottom line.

And if you are trying to go solar-only, need to size components for worst case, figure a 3-4 day buffer with poor insolation conditions.

 

[john61ct]

Victron SmartSolar

Best to find 40+ VOC rated panels for MPPT, not the usual low voltage stuff targeting consumers with cheap PWM.

Framed not "flexible" crap.

One SC per panel for optimal partial shade handling, say 75/15 can handle 220+ watts up to 260-280 if you get a good deal, look for local sellers, leftovers from house/commercial projects.

 

[john61ct]

Stick to 12V or 24V for storage, DCDC conversion is fragile and wasteful.

 

[Bikegirl]

A proper energy budget, in Ah per 24hrs is really the starting point.

Use a coulomb-counting wattmeter to measure the actual Ah used over time - duty cycling between peaks vs low continuous needs to be taken into account.

And don't bother measuring grid power appliances at AC voltage, need to include the inverter overheads.

So say your induction hot plate (as a thirsty example) uses 35Ah over an hour of making soup or spaghetti sauce.

You then guesstimate you'll be using it an average of 40min per day, so ballpark 25Ah/day is your budget for that load device.

Do the same for screen device charging, lights, fans, your fridge etc. until you get a total Ah per 24hrs bottom line.

And if you are trying to go solar-only, need to size components for worst case, figure a 3-4 day buffer with poor insolation conditions.

Hi John, we have another system on the boat for charging other stuff so the bike battery will be used exclusively for the 40L fridge and loading I have mentioned was from someone using the fridge at 12v at 32 degrees which is midsummer temps for us.



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[Bikegirl]

Stick to 12V or 24V for storage, DCDC conversion is fragile and wasteful.

Hi John, I don't have much experience in DC conversion. I understand it's lossy (not efficient) to change voltage but what is fragile about it?

I am trying to save money by using a large battery I already have to set up a system. Do you think it would be "less lossy" to setup an inverter off it to have 240vac rather than 12vdc?


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[john61ct]

Absolutely not, avoid appliances designed for grid AC use as much as possible.

Good quality converters are expensive, and that just buys better reliability not efficiency. Cheap Chinese are disposable and highly overated if it says 40A use it for 10A, maybe.

Saying "well I have this 52V battery might as well use it" is penny wise pound foolish.

Not to mention **huge** fire risk, don't sail farther from sure than you can swim.

If it's not going to be used for your ebike, sell it, or atomize the cells and reuse it

Li-ion don't last that many cycles anyway, a tenth as long as LFP.

But yes LFP is expensive.

The best battery value by far is Duracell (actually Deka/East Penn) FLA deep cycle golf cart batteries, 2x6V, around $200 per 200+AH @12V pair from BatteriesPlus or Sam's Club. NAPA relabels it here: https://www.napaonline.com/en/p/NBP8144 Deka self-labeled also sold at Lowes.

Finally, a dedicated Starter batt is OK, but you really should have just one House bank, for many many reasons.

 

[Chalo]

Stick to 12V or 24V for storage, DCDC conversion is fragile and wasteful.

Hi John, I don't have much experience in DC conversion. I understand it's lossy (not efficient) to change voltage but what is fragile about it?

Typical Chinese DC-DC converters crap out frequently even when run at a fraction of their rating. They crap out consistently if you expect them to run at their rating.

 

[Bikegirl]

Thanks for that guys. I think i will stick to FLA for this purpose. just hoping to get some more use out of my larger ebike batteries

I've got a 85ah 12v FLA so just getting a victron MPPT controller.

 

[john61ct]

Not enough capacity.

Even if every days is optimal insolation, you will burn that batt out quickly, even if it is brand new.

Using 50% of capacity is what gives reasonable longevity, and usually 2-3 days' buffer is a good idea.

 

[999zip999]

CALB CA100 3.2V 100AH LIFEPO4 PRISMATIC CELL - FULLY TESTEDBattery Hookup
CALB CA100 3.2V 100AH LIFEPO4 PRISMATIC CELL - FULLY TESTED
Regular price$48.00
these are $25 each or a hundred bucks for 4 you have a 12-volt hundred amp hour battery lifepo4 easy to boltl together.
I guess I didn't do that right but it's from battery hookup in United States. Just put balance wires on and a alarm under 5usd.

 

[markz]

Longevity is not storing at full voltage, not maximizing discharge rate that heat up the battery.
Not heating up the battery.
From what I read/saw(Grintech video) 20-80% vs 0-60% charge isnt a deal breaker.
I wouldnt leave it at 0% or 20% after I am done riding. I would charge my lithium ion battery back to storage for my li-ion @ 3.70V/cell. Though theres talk about Lifepo4 calb for high Ah on low # of Series cells (12V), diff voltages and diff characteristics.
However what I am talking about is all ebike terms, because you are using your battery a lot.
I store my 14S 52Vnom 58.80Vmax at 57.00V (4.07V/cell) overnight then use it the next day.
If I know I wont be riding it the next day I store at 52V or 53V which is storage voltage of ~3.70V.
Things could be different with Lifepo4 and non-constant use situations, non constant discharge, low constant discharge whatever "camping" battery means.

Its interesting to make that comment to not use below 50%, I will have to confrim for myself.
Actually found it pretty quickly
Remember though he's talking about ebike application, Lithium Ion application (not lifepo4, lead acid etc) video was back in 2015
not camping, storage, solar or backup.
https://youtu.be/IxB2j-egWcQ?t=1077

 

[999zip999]

lifepo4 can take a higher State of charge and be left there. SLA shouldn't be left better low charge is best to float charge sla. if left too long at a low state of charge is bad for the SLA batteries.