Re: (ET) Multi-bank 12V chargers

["David Roden" <etpost drmm net>]

On 18 May 2017 at 11:38, Ken Olum wrote:

> Minn-Kota MK460 ...

I have no direct experience with that charger.  

That said, multi-bank chargers seem like a good idea, but you need to be 
pretty sure of reilability.  I know someone who tried a different brand 
(sorry, I don't remember what it was) many years ago in a road EV.  He had 
multiple failures.  

I'm not 100% sure I'm remembering this history right.  It's been a long 
time 
and I may have 2 or 3 different EVers mixed together in this.  But if 
memory 
serves, the first time it happened, he drove the car without realizing it, 
and reversed that charger's battery.  The charger manufacturer replaced 
the 
charger, but wouldn't pay for the damaged battery.  After a couple more 
failures he went to a series charger for the entire pack (144v, IIRC) with 
shunt regulators on each battery.  (That has its own failure modes, but 
they're apt to result in less dramatic damage to batteries.)

One advantage of using 3 fully separate chargers rather than a bank 
charger 
is that you can keep a 4th charger around as a spare, in case one charger 
takes a powder.  That's probably cheaper than keeping an entire spare 
3-bank 
charger in the garage.  

> they will not disclose the exact algorithm used in their charger. 

Are they trying to sell to OEMs?  I don't know an engineer who would 
choose 
a charger for his product if he couldn't get its profile details.

Another question, is the charger manufactured in China?  It's really hard 
to 
keep "intellectual property" secret there.  There's a decent chance that 
by 
now some other Chinese electronics company (maybe even a division of their 
own subcontractor) has cloned it.  Check Ebay and Aliexpress to see if you 
can spot a similar-looking no-name at half the price. 

> It is very slow to start up, not reaching full charging current for
> about 10 minutes ... 

That seems like an odd design choice.  

As I mentioned before, lead batteries need an intial charging current 
that's 
as high as possible.  For golf car batteries, 100a wouldn't be 
unreasonable.

It doesn't have to last more than a few minutes (maybe even seconds), but 
that initial blast of current somehow makes the battery take the charge 
more 
readily.  I'm not an electrochemist and I don't know why.

Some batteries need it more than others.  I remember back in '96 that 
Solectria (the now-gone EV development and conversion company) was 
offering 
EV hobbyists fire-sale prices on Hawker Genesis batteries.  I found out 
years later that they'd bought a huge stock of them for their Force 
conversions, only to learn that their chargers of the time couldn't hit 
the 
batteries with enough initial current.  They switched to East Penn gel 
batteries, which were (and are) more forgiving; problem solved.

Here's an intriguing idea.  If all you need is seconds at high current 
(and 
I'm not sure that's true), I wonder if you could use a supercap or 
ultracap 
to deliver the opening jab, and then finish the charging with a more 
modest 
charger.

> and the transition from absorption to float seems to me to be at a
> rather low current. 

If the battery is really fully charged, float current should start at zero.

That said, IMO there's no reason to use a float charger with an ET.  It 
might be different with your Ox, if it presents parasitic loads on the 
battery when it's not operating.

With fairly new batteries that are kept clean and don't have parasitic 
loads, self discharge isn't really all that high.  This is especially true 
with AGM and gel batteries.  Many good ones can sit for more than a year 
with only a few percent of SOC loss.  

Unnecessary float charging leads to positive grid corrosion.  That's why 
you 
have to change the battery in your computer UPS every few years, even if 
you 
never drain it.

Speaking of such matters, my Cliplight (Exide) chargers are themselves 
parasitic loads, so they can't be left connected permanently. Their analog 
shutoff and polarity-protection circuits draw about 16ma from the 
batteries. 
That adds up.  Ignore them for a week and you've lost 2.7ah. With my 
batteries, that's almost 5%.

What their modern equivalent does, I don't know.


David Roden - Akron, Ohio, USA

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