Limiting Amps to Controller

[rollingreenhills]

Hello,

A question.

I have 24v SLA ( 2 x12 - 22ah) which I am am going to run a 48 volt BPM 500w from.

I am using a 20A step up transformer, to get from 24 to 48 volts.

The specs say the transformer will provide 500w of power to the controller, I expect the controller would take 750w atleast if it was there (?).

So the question . . will this damage the controller, or will the controller think the battery is flat and not work? Is there any possibility of damaging the controller.

I appreciate the bike will underperform, but I would appreciate any pointers. Thanks.

This is the controller and motor: http://www.elifebike.com/peng/iview.asp?KeyID=dtpic-2013-9T-FNM6.74VME

The bike as is is here: https://endless-sphere.com/forums/viewtopic.php?f=28&t=80029

 

[major]

Transformers will not work on DC, they need changing current as in AC. And typically the controller limits current. The BMS and/or fuse may get into the act also.

 

[wesnewell]

Assuming you have a 20A 24V-48V dc-dc step up converter, you will not damage the controller. However, if the controller max amperage is more than 20A, you may damage the converter. Looks like that comes with a 19A max controller, so it should work. I'd be surprised if you got more than 5 miles out of that setup though. You'd probably get twice the range with a 5ah 12s rc lipo pack.

 

[rollingreenhills]

I can confirm it is a DC DC transformer.

Thank you for your replies.

Yes, I think you are right about the range, as by doubling the voltage I am also doubling the amperage (on the battery side). So I suspect a range based on about 75% of 11ah, which is bunk.

Unfotionatlky funds will not stretch to a lith ion pack (which I desire) at present.

Are headway (screw together) cells the best you can get, or is that a matter of opinion.

 

[wesnewell]

Lead batteries can only output their total capacity at about a 0.2C discharge rate. That's 4.4A for your batteries. To get 19A @ 48V you'll need to pull 38A from your batteries, not accounting for loses in the converter, so at least 40A. I wouldn't expect much range and I'd also expect to kill those batteries pretty quick. I only use rc lipo. Lifepo4 is no good for more than a 2C discharge imo, even though Headway rates theirs at 10C. Their longevity test are done at <1C. Probaably 0.2C to compare to lead.

 

[rollingreenhills]

I think you might possibly be wrong regarding discharge rates.

The setup as (24v 500w) is pulls 25A + when under load, and spec sheet shows max discharge rates of 30+ amps.

http://www.batteriericaricabilionline.it/files/LC-XC1222P.pdf

I have used these one of these batteries to jump start my car.

With the RC Lipo packs, how do you use them in series and then charge them afterwards? Do you need to charge each one separately?

 

[friendly1uk]

Its £60 worth of lipo and a £20 charger plus a bms to manage it all. I think I have a 12s bms here in the UK that has been bench tested but not fitted. All in your looking at about £100 and after assembly it's as hard to charge as your phone.

Have a mowsie https://endless-sphere.com/forums/viewtopic.php?f=14&t=56886&hilit=yginrut

 

[ccmdr]

Just from a 15ah headway cell user. Having 17S2P of them at 65amps, they really don't 'appear' to have any issues, voltage sag is negligable in warmer weather (10+C). Biggest issue is the sheer size, weight and space required.

If you run a true 15S without the transformer you'd be fine with LiFeP04 or go cheap with the RC as f1UK rightly says, and go 12S. Tbh if your only pulling <2C for a sub 1000W system the LiFe becomes a tad more appealling. BMS is the right way to do it either way, series is your standard daisy chain on either side of the cells + to - simple :

ie. for 12S from red + side +-+-+-+-+-+- to - controller side
from black - side -+-+-+-+-+-+ to + controller side

BTW crazy setup on the front wheel from current build, likes it . Just be aware of import costs as a UK user, EVPOWER, ebay and the like come in cost effective when including VAT & shipping.

 

[wesnewell]

I think you might possibly be wrong regarding discharge rates.

With the RC Lipo packs, how do you use them in series and then charge them afterwards? Do you need to charge each one separately?

Yep. I thought you had 12ah batteries. I'll fix it to reflect 22ah batteries in a bit.
I charge them in series with a 100.8V charger.

 

[rollingreenhills]

Dear ccmdr and wesnewell,

Thank you for your informative replies.

I am a fan of reliability & reparability. Which is why I like the look of headway, but they are expensive and big. I have quite a large battery storage compartment under the rear bench seat but I am limited to 12ah cells because of their height, headway 15ah make for tall pack.

I can get a 20ah sanyo 18650 celled lithium on aliexpress for £300 shipped, a pouch celled 20ah on ebay for £300, but the RC LIpo seams a bit cheaper, I just need to get my head around the concept of charging them. A UK sourced 15ah headway pack is £500!

Ideally I would like to charge is parallel . . . . I have seen connectors for doing this on hobby king. DO they work?

Sorry ccmdr when you say BMS, do you mean the web retailer or the circuit board

EV-Power - Awesome completely missed that one!

 

[wesnewell]

There are all kinds of ways to charge. I've parallel charged as many as 12 lipo packs at once. Maybe this will help.
https://endless-sphere.com/forums/viewtopic.php?f=14&t=39666

 

[rollingreenhills]

That looks really complicated. Bit beyond me I think.

I have spotted these:

http://www.ev-power.eu/LiFeYPO4-batteries-12V-1-1/LiFePO4-Battery-Pack-12V-12Ah-PCM.html

Which seem hassle free.

I also need to run 12v lights, so have 12 volt batteries is a bit of a bonus.

 

[wesnewell]

Those won't work well. Look at the discharge rates for them. 5A nominal and 18A max. A 10ah 20C rclipo pack is rated fro 200A nominal.

 

[ccmdr]

eclipsebikes maybe your go to place for a UK based seller that sells 8-10-15ah headways, CC/CV chargers and BMS (not the website ). DIY pack of 15s 10ah inc BMS n charger £300. EVpower have the older QSmotor at reasonable prices too, but maybe a couple builds down the line as you'll need to be happy lacing a rim from scratch, take future builds into consideration with BMS constant and burst Amperages .

Tiz all conjecture, only you know whats right for you though .

*Edit* 12v can be acquired from a very cheap DC-DC from amazon, sub £10 without the faff of heavy, bulky, low performace 12v SLA cells - leading to poor cell life . Always best to keep cells balanced than tap out a 1/4 of the pack for lighting.

Get your head round the BMS wiring/charging and you'll end up with a much more trouble free, low faff EV experience than most other methods .

 

[rollingreenhills]

Thanks ccmder you are a mine of information.

I have seen the step down transformers, and I take you point about balencing.

Thanks again, I appreciate your advice.

 

[dogman dan]

For now, it would make some sense to buy another 12v 22 ah lead battery. Then the kit runs without the darn converter on 36v.

Later, get a 48v 20 ah lithium pack. Sanyo cells or something similar. Cheap ones (not the best cells) can be bought straight from china by alibaba, Better quality battery get from EM3ev.

Lead sucks, yes. But in a size that big, it will work fairly well except for the weight. 22 ah will suffer a lot less peukerts effect than smaller lead packs.

BTW, your bike is badass. I hadn't seen it because I don't read the non hub section of the forum much.

 

[d8veh]

You've chosen the right motor. The BPM can provide masses of torque. At 30 amps, it'll spin your wheel. Personally, I'd fit one in the rear rather than the front to avoid the spinning. They have the 36v code 10 (300 rpm) in the rear version. Elifebike don't make it clear what controller you get. The maximum current is an important characteristic. Another one is the motor maximum speed. What size wheel do you have? If smaller than 26", those motors might be a bit slow. They look like 20" wheels, which would mean 13 mph max from the 48v one compared with 17 mph for the 36v rear one.

 

[rollingreenhills]

Why thank you dogmandan, what a Gentleman.

I got hold of some 8ah lifepo4 cells yesterday. They are headway ones screw end type. So look like I am building my own pack.

I would have liked more than 8ah I must say, but the tought of spend £300 on a dubious impoted pack did not appeal to me, nor £500 on a headway one sourced from the UK.

As is I think the 8ah pack, will cost about £200 all in, and I will be able to repair it is it goes wrong or upgrade to 15ah cells in the future.

I have order a controller and charger from eclipse bikes.

I have high hope regarding the torque d8veh I ahve the 230 rpm version which should give be a little under 15mph. That is the max we are allowed in the UK.

Thank you both. I have ordered all of the bit now, and will post a pick when finished.

I managed to find a 20" steel fork with disc brake mounts so I am super happy about getting a decent front brake!

 

[rollingreenhills]

Well I can report back that the step transformer did not work.

It was OK on flat ground but as soon a a hill was involved, the controller would cut out.

Does the transformer drop the voltage to increase current? I do not know.

Write Up:

http://dorkythorpy.blogspot.co.uk/2016/05/using-step-up-transformer-to-run-ebike.html

 

[rollingreenhills]

Oh by the way aren't electronics unforgiving.

I have fried a BMS, and lost 3% of my hair over the last 2 weeks! :lol:

 

[999zip999]

You are making it harder then it is.

 

[rollingreenhills]

I think most thing are hard to do, when you are starting out.

My electrical knowledge was very low when I started this, and still is fairly low now.

I know all you guys on here are tech heads, but I am not.

 

[Voltron]

WelI just looked at your bike... its crying out for more batteries! And the series/parallel charging is no big deal.. I actually do it with my 72v packs.. they're made from two 36v batteries each, so they can be unplugged from each other and charged with a regular 36v charger (or 4! lol)


Way cheaper and easier to find than a 72v.