Charging Problems

I have new / newer items that are not working properly .

A little less than a year ago I bought a iSDT T8 DC charger,
I was using a 12 volt meanwell 250 watt charger but sold it along with my first bike conversion .
So
I started using a HP power supply that I modified , but it is only 12.27 volts output 750 watts , it worked ok but not enough for charging 3 or more batteries at the same time in parallel . ( you get less than half of that 750 watts when it is feeding the charger only 12 volts . I do not know the math but someone here does )

So Then I bought meanwell ERPF-400-24 from China ( big mistake buying from China ! )
It was advertised at being able to charge up to a little over 16 amps, and since it is 24 volt it should, However it heats up and buzzes at anything over 10 amps charging, less than 10 amps and it does not buzz , but still gets very hot. I have to put a high speed fan a few inches away to keep it operating .
So
I thought I would just bypass the power supplies altogether by buying a large Marine/RV deep cycle battery and run the iSDT T8 charger off the 104 amp hour reserve 12 volt battery.

Then I found another problem , the iSDT T8 charger shuts off at an imput of 11.3 volts , good you say ?
Well
The problem is that the iSDT T8 says it only has less than 11.3 volts imput, but the Deep Cycle Battery is reading 12.6 or more volts , even for the few seconds that the iSDT T8 runs .
I even connected 2.5 amps of charging to the Deep Cycle Battery to insure there would not be a voltage drop, which there is not down to under 12.6 volts anyway as I found out by measuring it while under load.

I went to the vendor's website and found a review by someone who bought a iSDT T8 and he said his shuts off at 11.3 volts.
( I do not think he even measured his battery to see that the problem is not with the battery , the problem is with the iSDT T8.

So now I am thinking about having someone make me a battery pack from 18650's or 21700's in the form of nearly 28-32 volts , maybe even 36 volt pack since the iSDT operates at up to 40 volts input
But then then another problem comes up. I want to charge several batteries at a time. 20 amps to nearly 30 or so amps.

So Then the question is , how many round cells would I have to have put in parallel in order to get a constant charge rate of 20 - 30 amps constant for an hour or more ?

And which cells are up to the task of higher constant amp output ?

You want a robust quality mains power supply that puts out at least 1200W for overhead.

Here's the mystery math, you really need to master these basics rather than just experimenting throwing money.

40V is top of the allowed input range, at that voltage only 30A would get you to 1200W, but higher rated current is fine.

Better to go a bit lower on voltage.

35A is the **most** it can pull, so you want a PSU that is capable of 40+ amps for overhead.

1200W ÷ 35A, call it 35V

that is the **lowest** voltage you want to get the full power this charger can produce.

So easy peasy, you want a "36V" PSU rated for 40A or 1200+ watts

If not actually putting out exactly 36V which would be fine, a 36V charger designed for lead would be well above 40V output, that's too high

Make sure its output can be adjusted below 40V, 38-39V for overhead would be fine.

Mean Well is a great brand, but you need to buy the right size unit. Has to be sized to handle **higher** amps than your charger will ever pull.

ERPF-400-24 is only 400W !

400W ÷ 24V is around 16A

The overcurrent protection on those does not allow it to continue working past that point, just shuts down, and very stressful.

Obviously keeping the size of the bank you're charging small, or setting the T8 below the watts your PSU puts out is the other way to go.

If you stick to 24V, then you will have a limit set by the T8 (35A) of 840W, say 1000W for overhead.

But I reco getting up to 36V

https://www.mouser.com/ProductDetail/MEAN-WELL/HLG-600H-36A

ELG or HLG are better Mean Well lines than ERPF, you stack them in parallel to get higher power if 600W is not enough.

If you do end up wanting to power your T8 from batteries (why?)

Then use Deka / Duracell deep cycling GCs at 6V each around $100 from Sam's or Batteries Plus, only 50¢ per Ah and if you take care of them right will last many many years.

Those "marine" 12V batts from big box or auto supply are not designed for deep cycling, will only last a few hundred uses.

Thank You

I want to charge from a battery for a couple of reasons.

1) every power supply I had got hot and was already enough $ for me even at under $ 100
that HLG-600H-36 Houser/Meanwell would cost apx $ 215 with Tax and Shipping .
I would rather put that money into a battery that I can transport
and
use as a power back up when PGE shuts off power here in California . ( Because of the many fires the last few years they are now going to be cutting off power often in areas where a fire starts , we are going to have a very active fire season here in California this year the experts are saying.
I am even preparing my self mentally for a possible evacuation from my home area sometime this fire season , which will last though October.

2) I want to start riding off road trails , some of which are an hour or more away from home , I want to only have partilly charge batteries in the car . ( it was over 100 degrees outside yesterday so even hotter in the car/trunk and I will be transporting them in the trunk )
I would like to ride off road trails with smaller battery packs , so will charge in between rides while taking a break/lunch/drink etc..

Since I live in an apartment , as much as I would love to have 4 6 volt real deep cycle batteries you speak of , even having one on my porch is pushing the limits of lease rules .
Those of you who live in houses probably do not know how lucky you are .


I am starting to look at the iCharger 8 , it will operate on voltages down to 10 volts , but is $ 130 so must wait till it goes on sale .

john61ct said:

If you do end up wanting to power your T8 from batteries (why?)

Then use Deka / Duracell deep cycling GCs at 6V each around $100 from Sam's or Batteries Plus, only 50¢ per Ah and if you take care of them right will last many many years.

Those "marine" 12V batts from big box or auto supply are not designed for deep cycling, will only last a few hundred uses.

Click to expand...

To use a battery bank as a charge source, it must be **much** larger Ah capacity, and at a high enough voltage to suit your DCDC charger at the Watts output you need, as outlined above.

You did grok all that math right?

Do not build a custom LI bank as a charge source, waste of money.

3x cheap sealed-lead Vmax @12V may be OK, but I would not bother with less than 20-30Ah myself, and you'll only get a small fraction of the lifetime cycles those EPM would deliver at far less cost over time.

So, whatever lead you buy, keep them in the car, rotate to charge off mains in the apt, get a box or bag that works, no one will know.

I lived for years all my van-dwelling's House energy, 40-100Ah per day came from coffee shops.

I called the vendor that sold me the iSDT T8 charger , he said it might be a connection / solder problem with the wires/xt60 that goes into the charger.
Got home and tested it and it is good, reads the same as the battery. He wants me to make a new cable , but I do Not have to the one I have been using for a year now is working perfect.
So
Then I brought out a charger from a few years ago, ( it only charges up to 7 cell packs .
I then used the same B.Box Store battery, 12 awg wire leads from battery to charger , everything the same except for the charger ... it works .
I even test charged two batteries in parallel then another two.
It all worked . ( however the charger can only charge at a max of 7 amps, and with the larger 7 cell batteries just under 6 amps so I still need a higher amp hour charger )

So
The problem is with the iSDT T8 charger ! ,,, now lets see what the Vendor will do ?

I have been thinking the same thing as you in regards to a charge battery,
2 or 3 smaller 12 volt , AGM batteries and return the single RV battery .

How many Watts do you think you were trying to pull, compared to the PSU specs?

How many do you think is the max you will need?

2 , 8 cell batteries trying to pull 11 amps to charge so 5.5 amps for each battery , so apx 30-32 volts X 11 amps
or
2 , 7 cell batteries also trying to charge at 11 amps , so apx 27-28 volts X 11 amps.

Will want to charge 3 to 4 batteries at a time so I would like to charge 5/6/7/8 cell packs on the parallel board at 16-20 amps .

The Meanwell gets hot doing just 2 or 3 packs at 10-11 amps , it is rated at 16 amps , but the sticker on the case says 16 amps when using 200-240 volts imput and 8 amps when using 100-200 volts imput. So spec's on China website was not accurate ( BMS Battery ) .

Did some more testing, I took old an car battery and older 7s battery charger that charges at a max of 7 amps and it worked on that battery as well.

The Problem , Really Is with the iSDT T8 charger !

Looks like for Field Charging ( Trail Head Parking lot Charging ) I will just use an old car battery and old charger ( not sure how many reserve amp hours those have since they do not list it ) ,
and just leave the 8 cell batteries and iSDT T8 charger at home .

Also looking into a few 12 Volt AGM batteries ... the Cost is way too high and they have very little reserve.
so those are now out .

john61ct said:

How many Watts do you think you were trying to pull, compared to the PSU specs?

How many do you think is the max you will need?

Click to expand...

Yes, your needs are small but use high volts anyway once you get the ISDT sorted, a couple hundred here and there is just what it costs to do this stuff right, live on ramen a while

There are few true deep cycling AGM, lots pricier and shorter lived than FLA.

BTW capacity is just Ah at the 20-hour discharge rate.

"Reserve" is a Starter batt thing, not relevant for deep cycling.

When charging you want get your batteries hot.