glider battery duration problems

Dan Marotta wrote, On 10/5/2013 8:22 AM:
This looks very interesting to me:
http://www.bioennopower.com/collecti...ifepo4-battery


On the surface it appears that I may be able to wire two of them in
parallel (or series-parallel if individual cells) and enclose them in
the battery case that fits in the tail of my LAK. I'll measure it today
and see if there's a chance.

Be certain to read the user manual for this battery, which specifically
states series or parallel operation is not recommended! The manual also
states

"Only use 14.6V, LiFePO4 compatible chargers to charge the battery. The
charging current should be between 2A to 5A. If you need a charger,
please contact us"

Don't rely on claims for other Li batteries, like "any lead acid charger
can be used", but only go by the requirements of the manufacturer of the
battery you have.

Lithium based batteries must be taken more seriously than SLA
batteries, which are nearly identical from one manufacturer to another.
Lithium batteries, even LiFePO4, can vary substantially in their
characteristics, particularly with the type of BMS (battery management
system) installed in it, and may not even have one. Even the proper
storage varies considerably between Li and lead batteries.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)

Thanks, Chris

The batteries I'm looking at have a PCM/BMS built into each and the price
includes a charger. I just measured my tail battery case and it will easily
hold two BLF-1206T, 12V 6 AH units.

Then I read the spec sheet and found that the manufacturer does not
recommend parallel (or series) connections. I've sent them a message
including the dimensions of my battery compartments and asking for
suggestions.

I know they have a 9 AH battery that will fit in my baggage compartment
battery holder and a 6 AH battery that will fit in the tail, but I want
more. I estimate my current power requirements at 1.8 amp hours so, for a 5
hour flight, I'd need 7.2 amp hours. I guess a 9 Ah battery with a 6 Ah
backup in the tail would work for just about any flight I might want to do,
but as I said... I want plenty of power.


"Chris Nicholas" wrote in message
...
Dan, not wishing to teach granny to suck eggs, but if you go for
Lipo in the tail (or anywhere), make sure you have a proper
battery management system in addition to a charger â?" apparently
the significant number of fires in Lipos in model aircraft were due to
inadequate or absent BMS. Otherss here will have more first-hand
knowledge.

(The Lak FES comes with a proper BMS for this very reason.)


Chris N

"Dan Marotta" wrote

Then I read the spec sheet and found that the manufacturer does not
recommend parallel (or series) connections. I've sent them a message
including the dimensions of my battery compartments and asking for
suggestions.

If you talk to the other people (like RC) guys, discharge is not the
problem, but it is in the charging. If you were to put two packs in
parallel, provide a Y plug so that you can charge each isolated from the
other.

Jim in NC

Morgans wrote, On 10/6/2013 8:15 PM:


"Dan Marotta" wrote

Then I read the spec sheet and found that the manufacturer does not
recommend parallel (or series) connections. I've sent them a message
including the dimensions of my battery compartments and asking for
suggestions.

If you talk to the other people (like RC) guys, discharge is not the
problem, but it is in the charging. If you were to put two packs in
parallel, provide a Y plug so that you can charge each isolated from the
other.

It's OK to talk to the RC guys, but PLEASE follow the battery
manufacturer's recommendations instead of the RC guys. The RC guys are
using different chemistries, typically discharge rapidly (15-20
minutes), recharge rapidly, use special chargers, and do not use a BMS
(battery management system).

In addition, some of the things you know about SLA batteries can cause
you trouble when applied to Lithium batteries. Don't guess - look at the
instructions and data sheets, and talk to the manufacturer. Even the
people selling them might not be knowledgeable enough, because this is
new territory for us.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)

Please correct me if I got this wrong:

1.LiFePO4 with BMS are less likely to self-ignite compared to other lithium based batteries (or LiFEPO4 without BMS). But LiFePO4 still contain lithium and will make an intense and difficult to extinguish fire should they inadvertently ignite.

2.If an undamaged LiFePO4 battery self-ignites, it is most likely to occur during charging due to a malfunctioning charger or BMS. The battery overheats to the point of ignition due to internal resistance to the current applied by the battery charger.

3.If a LiFePO4 battery is charged while it is in a battery box, it may reach a higher temperature due to a reduced ability to dissipate heat to the surrounding environment. If it is a hot day or if the glider is in the sun, the charging battery will reach a higher temperature.

4.BMS have a fail-safe method of monitoring battery temperature. The BMS will suspend or reduce charging current should the battery temperature exceed a safe level.

5.The BMS makes charging a LiFePO4 battery, without removing it from the battery box in the glider, a safe operation. Manufacturers anticipate this scenario.

6.If I have a 5 AMP master fuse at my LiFePO4 battery terminals and I have a partial short that draws 4.5 AMPs. The BMS will detect any dangerous temperature rise and disconnect the circuit.

7.If the BMS is damaged in an accident, mishandling, or by age-related component failure, all bets are off. A LiFePO4 battery with a damaged BMS will be obviously "dead".

8.LiFePO4 batteries with BMS are compatible with solar panel chargers.

Thanks. When I finally make contact with the manufacturer, I'll bring that
up.

In the meantime, I'm thinking of fishing another pair of wires from the tail
to the cockpit. Since it appears that I can stick two of these 6 Ah
batteries in my tail battery box (which then slides into a compartment in
the tail), it should be simple to add another switch to the panel to control
it. I think two of these batteries are about the same weight as the three
SLAs in the box now and, due to their shorter length, would lower the mass
deeper into the fin.

"Morgans" wrote in message
...


"Dan Marotta" wrote

Then I read the spec sheet and found that the manufacturer does not
recommend parallel (or series) connections. I've sent them a message
including the dimensions of my battery compartments and asking for
suggestions.

If you talk to the other people (like RC) guys, discharge is not the
problem, but it is in the charging. If you were to put two packs in
parallel, provide a Y plug so that you can charge each isolated from the
other.

Jim in NC

Eric, I have absolute faith in my ram air parachute. Having said that, I
don't relish the idea of bailing out of a flaming glider!

Since I have no direct knowledge of these new-fangled batteries, I will
listen only to the manufacturer when designing my system. When and if I get
it done, I'll post the design.


"Eric Greenwell" wrote in message
...
Morgans wrote, On 10/6/2013 8:15 PM:


"Dan Marotta" wrote

Then I read the spec sheet and found that the manufacturer does not
recommend parallel (or series) connections. I've sent them a message
including the dimensions of my battery compartments and asking for
suggestions.

If you talk to the other people (like RC) guys, discharge is not the
problem, but it is in the charging. If you were to put two packs in
parallel, provide a Y plug so that you can charge each isolated from the
other.

It's OK to talk to the RC guys, but PLEASE follow the battery
manufacturer's recommendations instead of the RC guys. The RC guys are
using different chemistries, typically discharge rapidly (15-20 minutes),
recharge rapidly, use special chargers, and do not use a BMS (battery
management system).

In addition, some of the things you know about SLA batteries can cause you
trouble when applied to Lithium batteries. Don't guess - look at the
instructions and data sheets, and talk to the manufacturer. Even the
people selling them might not be knowledgeable enough, because this is new
territory for us.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email
me)

On Saturday, Dan Marotta wrote:
This looks very interesting to me:

http://www.bioennopower.com/collecti...ifepo4-battery

Here is another one you might take a look at if considering Lithium power. I have one of these on my other flying machine and it works well.

http://shoraipower.com/products

On Monday, October 7, 2013 12:44:54 PM UTC-4, Soartech wrote:
On Saturday, Dan Marotta wrote:

This looks very interesting to me:



http://www.bioennopower.com/collecti...ifepo4-battery



Here is another one you might take a look at if considering Lithium power. I have one of these on my other flying machine and it works well.



http://shoraipower.com/products

You should explain what Shorai means by (for example) "18 AH PbEQ" before you make such a recommendation. But I predict that once you understand this well enough to explain it, you'll withdraw the recommendation :-).

These are starter batteries. Unsuited for gliders.

T8