<div dir="ltr"><div>@Pete <br></div><div>I'm glad you guys are OK. The crux of the issue is that I haven't seen any LiFEPO4 charger ICs that handle more than 7 cells in series. Each of my three batteries have 4 cells in them, so I think I need to have one charger for each battery which charges the 4 cells of the battery in series.</div><div><br></div><div>I only get 1-2 hrs of working time a day right now due to my daughter's pre-school shutting down, so it will be a little while before I get a functional schematic out. However, I was tentatively thinking of using the following components:</div><div>NMosfets (used for all): <a href="https://www.mouser.com/ProductDetail/ON-Semiconductor/NVMFS5C612NLAFT1G?qs=%2Fha2pyFadugLwIkhTqkZTKk6f9YgRBDTRk6R4I0d7T5BfE4p4JIMyYRpkPiujU25">https://www.mouser.com/ProductDetail/ON-Semiconductor/NVMFS5C612NLAFT1G?qs=%2Fha2pyFadugLwIkhTqkZTKk6f9YgRBDTRk6R4I0d7T5BfE4p4JIMyYRpkPiujU25</a></div><div>High side NMosfet driver (for NMosfets which are not connected to ground): <a href="https://www.mouser.com/ProductDetail/Analog-Devices-Linear-Technology/LTC7003EMSEPBF?qs=sGAEpiMZZMve4%2FbfQkoj%252BKKapMsNT2INsri6aFIMPoQ%3D">https://www.mouser.com/ProductDetail/Analog-Devices-Linear-Technology/LTC7003EMSEPBF?qs=sGAEpiMZZMve4%2FbfQkoj%252BKKapMsNT2INsri6aFIMPoQ%3D</a></div><div>Single battery charger (would use 3 of these with a 24V supply): <a href="https://www.mouser.com/ProductDetail/Texas-Instruments/BQ24630RGER?qs=sGAEpiMZZMsZtvfwwjgKgY9Zc%252BP5Y9S3">https://www.mouser.com/ProductDetail/Texas-Instruments/BQ24630RGER?qs=sGAEpiMZZMsZtvfwwjgKgY9Zc%252BP5Y9S3</a></div><div><br></div><div>Same schematic with auto-annotation:</div><div><a href="https://drive.google.com/file/d/19qjaiqOR5wqI34htY-u9LFqNepMjd0cY/view?usp=sharing">https://drive.google.com/file/d/19qjaiqOR5wqI34htY-u9LFqNepMjd0cY/view?usp=sharing</a></div><div><br></div><div>Apologies if I wasn't clear. I've annotated the schematic. WIth the updated one M1, M3, M5 would be on and M2. M4 off during "normal" operation, resulting in ~36V from the 3 ~12v cells. During charging, M1, M3, M5 would be off and M2, M4 would be on. The idea is that M1, M3, M5 control charge moving from the high side of a battery to the low side of the next one, so disabling them isolate the cells from each other. The charger ICs seem to expect the low end of the batteries to be connected to ground, so M2, M4 being on makes that happen.</div><div><br></div><div>Given that during series ("normal") operation, M1, M3, M5 have an approximately 0 voltage difference between source and drain (and M5 requires a gate voltage relative to ground higher than the 24V the charger is getting), I think a gate driver with a charge pump is needed to drive the those 3 mosfets. Does all of that make sense?</div><div><br></div><div>Relays would be great in terms of functionality but I'm a little worried about reliability. The hub motors I'm using are brushless & direct drive with a lower mechanical load than they were designed for, so they might last a fairly long time. It would certainly simplify the design though.</div><div><br></div><div>Thanks,</div><div>Charlie<br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Sun, Mar 22, 2020 at 3:57 PM Shane Trent via TriEmbed <<a href="mailto:triembed@triembed.org">triembed@triembed.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr">Charlie,<br><div><br></div><div>It doesn't surprise me that Pete beat me to the punch on mentioning relays after you said "one battery at a time". I expect Pete and I share similar ideas. My though was connect each battery to the COM terminals of a DPDT relay and use the Normally Closed (NC) contacts to wire the batteries in series. When AC power is available for charging, you can use the relay's to pull one battery at a time out of the chain, check its voltage and charge if needed. </div><div><br></div><div>You would have the clack of mechanical relays but adding just two MOSFETs should let you get the full expected mechanical life-cycle from the relays. Include a strong N-type MOSFET at the bottom of your battery chain and in the ground lead of your charger (keeping the charger isolated from the circuit until that FET is enabled. These FETs allow you to ensure there is no current flowing when you open or close the contacts of the relays.</div><div><br></div><div>I expect the life-span of the relays will be more than sufficient to outlive the motors/gear train on the project. And using relays would make the functioning of the charging circuit easier to follow. Additionally, you can buy a off-the-shelf relay board for prototyping (I have used NCD boards on multiple projects). Let me know if you have any questions. </div><div><br></div><div><a href="https://store.ncd.io/product/4-channel-dpdt-signal-relay-controller-4-gpio-with-i2c-interface/" target="_blank">https://store.ncd.io/product/4-channel-dpdt-signal-relay-controller-4-gpio-with-i2c-interface/</a> </div><div><br></div><div>Good luck with your project,</div><div>Shane <br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Sun, Mar 22, 2020 at 3:27 PM Pete Soper via TriEmbed <<a href="mailto:triembed@triembed.org" target="_blank">triembed@triembed.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div>
<p>Hi Charlie! Jenny, Emily and I are well and happy.<br>
</p>
<p>Your circuit made me chuckle, 'cause when I was thinking of your
earlier posting I was going to share the scheme I intended to use
for charging a capacitor with a string of microbial fuel cells by
switching then between parallel and series connections. But that
was at silly low currents were analog multiplexer chips would
work. But the prototype was using relays. If you're interested I
could dig up the schematic. Definitely the Rube Goldberg approach
with relays, though, but your "one battery at a time" requirement
would make it simpler. :-) <br>
</p>
<p>Your schematic implies wanting to just charge one battery at a
time, but I can't see your circuit working past an initial point.
But I think it's in the right direction. (Nit: your schematic
symbols are for some kind of very generic FET transistor and I'm
sure you'd be using high current ones with body diodes, right?
Bigger nit: if there were part numbers we could more easily reason
about the wiring). <br>
</p>
<p>So numbering the transistors from left to right as Q1-5, then
with Q2 and Q3 off but the others on, that's "normal mode", right?
With Q1-3 off but Q4 and 5 on a lower voltage could charge the
third battery. But I don't see how you go beyond there with this
circuit. <br>
</p>
<p>Or am I misunderstanding this? At a minimum you'd have to arrange
for your single-battery charging voltage to reach the positive
sides of the first two batteries, right? So maybe have Q6 and Q7
between the right side supply and the "positive side" of Q1 and
Q3, using the Q3 and Q5 to disconnect paths as needed and then
perhaps a Q8 and Q9 to select between running the system to
conduct the higher "all in series" battery voltage to the load and
the lower, charger voltage to the one of three batteries. That is,
a SPDT switch above the rightmost net going upwards in your
schematic.<br>
</p>
<p>Alternatively, figure out how laptop batteries are handled. They
seem to be always one big series connection, but maybe the extra
connection pins we see are for this same approach? I have no clue
about that.<br>
</p>
<p>-Pete<br>
</p>
<div>On 3/22/20 1:09 PM, Charles West via
TriEmbed wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">
<div>Hey Carl!</div>
<div><br>
</div>
<div>I'm glad to hear that you are doing well. The 12v
batteries have built in balancers/protection. It's isolation
for charger that I'm trying to figure out. I think I have a
potential solution (<a href="https://drive.google.com/file/d/1JxSStAuKn-OMZUCreYQjGUVy5fR2ADpU/view?usp=sharing" target="_blank">https://drive.google.com/file/d/1JxSStAuKn-OMZUCreYQjGUVy5fR2ADpU/view?usp=sharing</a>)
with the NMOSFETs between each battery needing a high side
driver. The idea is that when the batteries are operating
normally, you turn on the between battery mosfets and disable
the to ground mosfets, then inverse for charging.</div>
<div><br>
</div>
<div>Does that make sense to you guys?<br>
</div>
<div><br>
</div>
<div>Thanks,</div>
<div>Charlie<br>
</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Sat, Mar 21, 2020 at 4:42
PM Carl Nobile <<a href="mailto:carl.nobile@gmail.com" target="_blank">carl.nobile@gmail.com</a>> wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div dir="ltr">Hey Charley,
<div><br>
</div>
<div>We're doing ok, I'm working from home 100% of the time
now.</div>
<div><br>
</div>
<div>This may not be the exact answer to your issue but it
may help. Banggood has a lot of LiIon battery protection
boards. You may be able to use one of these, it would make
the actual charger a bit simpler.</div>
<div><br>
</div>
<div><a href="https://www.banggood.com/search/liion-battery-protection.html?from=nav" target="_blank">https://www.banggood.com/search/liion-battery-protection.html?from=nav</a><br>
</div>
<div><br>
</div>
<div>~Carl</div>
<div><br>
</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Sat, Mar 21, 2020 at
8:17 AM Charles West via TriEmbed <<a href="mailto:triembed@triembed.org" target="_blank">triembed@triembed.org</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div dir="ltr">
<div>Hello all!</div>
<div><br>
</div>
<div>I hope the virus hasn't affected you guys too
badly. My little family's been pretty much staying in
our house for the last week and a half (since our
daughter's preschool closed), but we are doing OK
overall.</div>
<div><br>
</div>
<div>The work on the sidewalk robot continues! I'm in
the middle of testing a brushless motor controller/MCU
combination to drive the four hub motors that will be
moving the Mk3 robot. If all goes well, it will be
built like a tank and strong enough that I could ride
on it if I wanted to.</div>
<div><br>
</div>
<div>The part I'm trying to figure out is battery
charging/system protection. The motors expect 36V, so
I'm putting 3 4s LiFePO4 batteries in series to
provide it. What I'm not really sure about is how to
integrate a charger. Each of the batteries (<a href="https://www.amazon.com/gp/product/B07Q7FY8CC/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1" target="_blank">batteries</a>)
is meant to substitute for a 12V lead-acid motorcycle?
battery, with its own built in cell balancer. I'm
hoping to charge them with power from a 24V DC
regulator, potentially with a simple 2 terminal
charging dock.</div>
<div><br>
</div>
<div>The issue I'm running into is that none of the
charger ICs I'm looking at can handle 12 cells in
series (and they would probably require 40V or so if
they did). I'm thinking that I should be able to have
a seperate charger IC for each battery, but I'm not
entirely clear on how you would charge them in
parallel while having them connected in series. I'm
sure you can do it, because my other charger does it
for Lithium polymer, but I'm not sure what the
configuration would look like.</div>
<div><br>
</div>
<div>If I may ask, do you have any ideas?</div>
<div><br>
</div>
<div>Thanks,</div>
<div>Charlie<br>
</div>
</div>
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<div dir="ltr">-------------------------------------------------------------------------------<br>
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